- - - te6 treetmen-t can be found in e273-83, the :eoal of the work rep'orted herein was to...
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.REOT REPORT DOCUMENTATrION PAI , .1'EFORE COMPLETING FORM
.RE O NUMBER 2. G d 'C SION No. 3. RECIPIENT'S CATALOG NUMBE R
4. _T LE.tad- fnittr - - - S. TYPE OF REPORT & PERIOD COVERE
Te Design and Emulation of a System Kernel for'.'X-Tree 1 - Thesis
/ 6. PERFORMING ORAG. REPORT NUMBER
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V _ __ _____________
Li 7T~j
THE AND,1~ - ML' &T ION OF A SYTMKERNEL FOR
R Mzil Wagon~er
I LIC £Berkelev
X-treo_ is tree-structured network of siri9le-
chrat n s-o c emr ke re o s p rv s n the opera- A
tien o eah rocSesor s rege as omded o
futedre Peeted siorso this worki- Te add orefun-itos the ker i design imnstrate b e a rd sucs -
fu emulateion of he e T-tree exctn-asml
user ~ ~ 1 Prga.____sinsaeasomd o
March 30' 1979 Q~&IDIa TABIkimmounced3,atificatio
IstDis -- 1 a
j ]v
THE DESIGN4 ANtD EMULATION OF A SYSTEM KERNEL FORX - f REE
R N.il Wasonar
X-tree is tree-structured network of sing~le-chi=- Processors desisned for 1985 technolo:9:. Antoperatins~j s-:stemj kernel for supervising the opera-AItion of eamch r-rocessor was desi:9ned arid coded. To-test the crode? ann X-tree emulat or was written torun on t-he 1R' 11/70 UNIX swstemn. The kernel ---
internal structure and the emulation technieues-used are ?rF~sented in this papsr, The feasibilityof t"he Pkerncl desisr; is_- demnonst-ratedJ bv a success-ful emulation of th e X-tree executins- a simpleli uer rs'rosram. Suss estions are also made forfAture Rxtensions of this work to add more func- 4
tioe Fo te kenel and to ime-rove- the ransfe atd --
effPicienosiz of the emulation.
N1
A
V AIBPLE OF CONTENTS
I * T NTPflfiIC -rO ,\ ....... 1
2. DESCR PTION OF X-TREE
2.~: asic DescriPtior, .... ,*.. 32.2 Inter-node Communications ....... 5.23 Addressin2 Stru- re 7
3) .. DESCPFTION OF THE NO E KERNEL
WE3.1 Fun Cto n S Descri-l'tJon #3 2 Structural Overview.,3,3 F'ocess Mana:5ement
.4Messase ManagemTent 4,.. -8-3.5 Co, minicEtions Management- ....... 23
4. THF EMULATION FROGRAM4.1 X-Tree Nodes as UNIX Processes .4..4.274.2 Subprocesses nd Their S-rchronization .. ,...-33
" 4.3 Emulated Communicatiorn Hardware 4,,,#,*-39
5j, CONCLUSIONS5 Evaluation ofi the Kernel ,
A 5.) The Attempted Use of MODULA5 3 Subprocess Packa:ge Reconsidered -4 * 485,4 Future Tasks ., 44--4-50..
IL Append ices
A. Kernel Data Structure DiagranmsR. E-Emjlted Kerrel Code -:-IC. Pertinent UNIX Services
D . Instructions for Running the Emultor -v. Material or, Future Work:
Model of a Paged User Process-1 ' A MODULA Clock/Delav Driyer
M.rch 30 - 1979U _ _ __ _ _ _
.... .. . . . . . . . . ... .-= _ - : - T - - _.= E -
If the current trends in VLSI architecture continzue? it
will be Possible to pull a complete computer, including
njemrorv and communications hardwarey on a single chip' bv the
mid-1980s 16J, To explore various issues in the construc-
tion of large scale svstems fromi these sirigle-Chip comput-
er, uc a system is currentlv being designed at the-
Uriiveirsitd of Caionaat Berkelev. E"ecause of the topol-
u~~ oi~~ n~ atn im e- i~d X -t re
A bsicdetcription of X-tree arnd its concetsi ,oIL vided in ~section 2 of this Paper, Thiaconis ee-
a,, tl er brief and fmits details not needed for the
understanding~ of this Particu--ar Paper. A more coinolete
6 treetmen-t can be found in E273-83,
The :Eoal of the work rep'orted herein was to define -and
implemrent an op'erating svstem kernel 1103 for X-tree.- lAt
the time this P-oject was star-ted, almost all the work done-
n!-I X-tree had beern on the designw of the hard-iare -architec -
ture and the commruni cat ions network,+ Very little work on -
software had~ been done, in fact, this has been the fir'st
veal attempt tio Produce running software- for the stestem. -
Miarch 30, 1979
7! -
IIt2
Section 3 of this Paper describes tte definition and
inter-.al structurw of the node kernel. In section 4y the
vsrtous techni-es inted to test and run the kernel on the
UNIX svstem are discussed. Finally some reflections ard
closins comments are pre-sented in section 5.
2FIfig
M 9
Ns
C - I-
M a
- C March 3O, 1979
I _,, - . .. I I , ,
2. jIi2OfUCIOTN i0 X-IREE -
2.1. Basic flescziat+ioo
X-tree 's a connected network of sin.e-chi. computers.
Results of various simulation studies £32 have led to the "
selection ol a topoio- - which is a binars tree with some
additional interconnections at each level of the tPee. ManvIL different schemes for these additional interconnections have
been Proposed. No final selection h-as set been made. Pic-
tured below is an X-tree with 'full rind' intrslevel cornec- -
!ntins.
11 - - -
-( t e f t s -- a ------ - -=-- 3 l --- -
E a h dode in he tre s a 'ull scale comuter wiTh
on:-chip m..emorv and commun-ication hardware. All externil- s
d'Pvices (disks, ter.minals,? etc) for the s~stem- are connectLed .... 2
tothe downward links at lea"eves' of the tee, TheO .R,
are no external devices e connebted to the uOer
nodesr except a bootstrap device connected to the root nod * --
arch 30, 11979
- ---. . . . . . - . i.- --- ~- _ - - A _
p - -~_____ __ _
Jhn nodes in the tree are numbered using the simple
sonei"ustrated in the dia ,ani The relationship between
the nsumbers of connected nodes has a convenient eroperW (in
the binary representation):
(I) The number o' a left child is the number of the Parent
with an additional 0 at the least significant end,
2) The rumber of a-ht rhild is the number of the Parent
Snith an additional 1 t the leest significant end.
This makes env part c er node Is to locate.
I -
K
g
March 3O0 1 7I _J-2Y~
-=2.2. toter-node ComuicationsI
fIn such a s-stem, the transfer of date between nodes
Could bevery complex and timfie-consuming. For exaimple, data
from node I to node 4 must Pass though node 2. if the CPU
!in node had t- a ively transfer such data throuh Its
node! much rccessInS Power would bz consumed on this simpie
t ask.
To nged e * 3.o-<- . de*--_ s divideo into imessases. At
4t-he beginnlng of each messase is a field which contains the
nmber o- the non e to which the message is beins sent. Each
node ontsins a communicanEions controller which can route
iessa:5es ±:hro:gh t.e - without di r ect CPU involvement.
to arent
'on' -o
I Ir . -
1 - I.. - -
I] link "oscr r link
Sto left to rishtchild or h: 'dstntin
9 I, tins wa- r the C~ in each node is involved onils with mes-
s~e=for hichit i the se,-rce or f-ina! destinatioin.sages ror wh iti h
Further simulS-tions of the message traffic £93 have
reveled that it will be necessars to send multiple messages
U; ' March 30, 1979
I ;coor'ntiover each sIng link. This- isacconi4shed bs
t. t rhe lin-k Swoflt Several losical-1 channels-s
knw nXtee:nlt. Te iamFlesentati-On of the ;Com-
rnncataon rntrnle is aisciussed fullw; in £6. ortn
4 - ~r~oss ofthis Papery it s suIf f i cient to nt htec
sOt 1 senb- the CPU cs a sepaat d ,EOevice, independent
from the otr-h e r sc t s The interface to these slots is
descabe- ser=
I - March 30 7 9
171*e -l~ ido i-'e'
snaorr~1=te r- i7, fern
a I Convec-ntinad sse. Tofrso
neeorsolr are deied--f es
(1) Lcal amor~- the' rcg--*
Ix lo rSIO r- rete_ ~-rs
II .ces ~-'n oh ar attached to.the eies ofhtre
II n a -a=rS tlhs ano nrua ror : asts lal nee
0 n'- d~ ?me ?iclc-in the Melbalt
e
-S
Ho, Gbhe-n arelobsl meddressis refereentoi -b,=;~
Thi -WO
T:ic he 1-o-nvicer s '; attaceda.n-ch -elsey
tO PGITC octina ~ ~rrrad s he1ff-l1779- __Iii An00-4C~t~n Coba ~eor~ s r~anr tobs is NftE
() n identifier (ID) which is uriicwe within that led-f
nodey -ienerated bv the leaf node when the object i s
A ful Ibl adrs is the specif'ied bv an object NAI
arnd an offsetcwithi+ the object#
LWNAME NODE + ID
ADDES NAE4 FST NDE+I FSTA
In tAhis. wais, no --Thlbal table is needed to locate arV
:global address. A revuest11 for data is routed to the -1 e aF
node spcified in~ the object NAME. That leaf node then miaps
t he I D .nd of-"set into a location on the momror-d device aridI:~retrieves the reaua red --~e
441
FIE
f I
ZII
March 30, 1979
9 3.1~c~i~iio o1ibe Nocde Lemota1
:i.1. FurncLL rira. DescImiat on
T'he *rimar4 -goal of' the node kernel is to make Possible
the construction of the operating~ svstem -ard user Programs5
as sets of commuicating concurrent Processes [13# 1In par-SLticulary these Frocesses must be able to c'ommunicate with-ech other usins4 onl-: Process namesy rnot locetions within
the t ree,
The ser-vaces r'rovided b~d the kernel are necessarii
4uite P r iiiiv e. hev are con~cerned~ol with the creation
J and execution of' Processes and with the sending of messages-
3 -rom,, one Process to another. The operating~ smstent lever
conrstructed over the k--ernel will P-royide more general ser--
vices for the user,
SfThe relationshdip between t'.he k-.ernel and the upper 1 e V61-
operatini~ svstem cant also be -described in terms of' resources-
maniaed.
1. The la.errnel manages node CPU time and inter-node commun-
_ The general cperating svstem manages ?hasica-l- evX.*C'eS_
(disksi etc! and Processor assi~nmeitt#
To accomp-lish this, the kernel is impement~d- as -a-
Ssmall set of code which exists in each node of- the tree. It
miust performi three specific tasks:4
March 30? 1979
(1) M'ariac-e trie execution of Processes runnin:E on that nodev-
(2. Maria:Ee tile interfacE to the comrmunicationis cortioller,
(3Z Tdentifv messa!es to~ send them to their Proper deStiria"
In the discussions which follow, nio distinction is fitad e
between Processes which a~re P'art o~f the operatin.5 svstem and
Processes which Perform spFlicatiorns. For the Purposes of--
e ernel Y all such Processes are --orsidered asue
Processes.
-N-7
I __ ___ ____ ___ _ March -30, 1A979
____ a- --. 10IVT.As pointed out above, the kernel is a set of software
which resides in each node and supervises the user Frocesse.s-
and communication for that node# It is composed of several
p-arts,.~
1. independent kernel processes,
A set of device drivers for the communications channel,
3; A set of kernel service routines invoked bv users :
,-rocesses, end
4. Various subroutines for the performance of s-ecific----- -
tasks.
These Processes and routines can be grouped into thre6
blocks corresponding to the main tasks of the kernel: II.. Process Marna emert4 subroutines to create and start
user processes; kernel service routines to be itzvoked -
-_h- user Processes. -
2 Communrications Management: a set .of device-drivers, on e -
for each 'slot', wh-.ch move messages in and out of £-
-lode ;_. 4-
3. Message Management: the main Proces,: of the. kerel h. ..
various subroutines for mani-ulating messages; imatches I_user messages to their destinations and interprets ke.-
nel messases--to perform remote reauests, -
March 30, 1979 1
-12
SWhilIe these are convenient 4rours for understaridin:E the
st-UcLtUre Of the kernely it is important to realize that
thev ave riot independent of each other. For examrlef when
kernel service routines are called bw the userr the:Z accom-
RE~o the niessa:e jianagertierit group. 2
Cogmmunration between the three groups is accomplished
in Prirfarl- two wavs: E
A:Proces:;or roie ioe group m:e;call a routine in
as apuot antheunseles
aeues for laeprocezssin5.
Thle rrocesses of the kerrnel (arnd of the users- as well)
are to C)b -eue bv a hardware monitor suggested bw Tim-
Mcfcrear EJ T he iimp lement-ation, in the emulator is
described in chapter 4.
The kerniel imp-lemented for this Project has ignore~d
several sources of comlexitv in the X-tree. Firsty -it it-
envisioned thalE the X-t~ee swstem is to be indefintitel:
E ~ extensible; hence node numbers mav have art uribounded:!
len gt h In order to focus on other is-sues; a fixed ler.gth-
n-ode number of 16 bits was Postulated for the kernel. this-
inot -eallv a sev'ere restriction -since this lengthi -wkkl
March 30t 197?
I -13-
support a tree of 16 levels, a total of nodes!
The second simplification is far mrore serious: the P a- Iins of' X-tree is riot em.ultedJ Insteady all code and data
structures for user Processes are included diectly in the
em.late d node that the -rocess is rurning in.- The addition
of P'asir: to the kernel at a later date is not absolutelv
strai_-htforward, but an attempt was made Lo keep the code
compat.ible witlh Pa:irg and the use of full _5lobal addresses*
A model of user Processes under the full Pa:aed systeT is-
described in apperdix E, A
It is also assumied that all messages in X-tree are
reliably transmitted. Later versions of this kernel wil:-
- need to herdle messsa!e communiction failures.
SS
NNJ
A
Mac=0,17
iT 14-
The P'rocess Merna: er consists of' all the code necessarv
to suprport user .rocesses. in Particular, the followingP
p rts are included?
1- Two routines for startin.q and creating user processes.
2- A set of. kernel service routines called bw user Pro-
g rams.
-ach user Process is represented bw a Process control
block (F'-B) of the f'orm
link Field :--used for the FREEFCB
- linked listfull process name -->ider:tifies the process lobll "
I status word (psw" -->internal Process status? such -as"I - - - -condition codes, etc Aexternal status word -- >state of the Process* IN-USE-- - - -WAITING-FOR-Io etcsemapho'e Pointer !--used for emulator e-nchroniztion A
IOB lit Pointer -->ointer to ,he Process's list.'bf......- active !0Bsname of Parent
--------------------------------------
-ro, r=M Counter qs~~tack Poin~ter ::-
* I
A fi<xed number of these blocks exist in each nodei 9
T -is sets an effective upper limit on the numiber -f- -
_rocesses active in node at one time-
Each Process can be identified in two wais- _ --
March 30, 1979
-15-
(1 Bv s full 32-bit name which is composed of
S(a, the node nu'mber of the node that the Process"s
J work space is or,. and
(b -an ID n,mber suaranteed to be uninue within that
node.
(2) Bv a Pointer (PID) to its F'CB' this is used onlv within
the local node kernel.
ITr- nraslaion from the local name to the full name is
sipie it can -e retrieved from the second field in-the
PCB. The "-er direction is a little more complicated+ A
hash tabie is maintined to hold pointers to all active PCBS
1( irn the n'da.
7or the emulatio:? an additional set of kernel sub-Li -rocesse - is defir:ed one 'for each PCB in the node. Each-- can be thouht or as a sub-rocess reserved to execute a
user. At sustem start time7 each of these subprocesses 'does
i-,,mediately to s'i-e=O. Also, all of the PCBs are linked
together in a list of urused PCBs (the FREEPCB nueue).
The creation of a new user Process is Performed bi othe
subroutine KCRTUSR. Its implementation it straightforw'd. -
An unused F'CB is obtained from the FFEEPCB oueue and is-
filled in with the appropriate information, specificallv-the
• rioritv, stating program counter, and the name of -thL j
Parent Process. A unioue full name for the new Process -is-
March 30, 1979
J then generated, stored in the PCB and the hash- table, and
Passed back to the Parent process for later use.
The subroutine KSTRTUSR starts a specified user Process
and is ecualiv simple. Using the hash table, the Process PCB
is located and the correspondin kernel subprocess (the one
dedicated to that PCB) is awaKened. This subprocess then
(.3) Runs the user to comFletion,
5_U
(b) Irenoves the Process name from the hash table,
(c) F'uts the PCB back on the FREEPCB aueue for later reuse#
( d) Goes L:ack to sleep.
Ai Kernel Service Routines - Five functions are Provided
4n the -resent kernel as service calls for the user, These
are described below.
P'CREATE 'N-,DE, START, PRIO, PNAME)
Definition: A child Process is created. The argumentsNODE, START, and PRIO specifv the node number, startiIsglobal address and -rioritv of the new Process. Once-the new Process has been created, its full process namewill be returned to the caller in PNAME.
Implementatior It NODE is the current node number,routine KCRTUSR can be called directl. If not,a message is formed and sent to the kernel Processon the Proper node. The return message, whicncontains the new Process name, is then waited for.
F'PSTART (FPNAME)_ Definition: Starts the execution of Process PNAME,
where PNAME is a full Process name*
k Implementation: Similar to PCREATE except of coursethat KSTRTUSR is called instead of KCRTUSR.
- March 30, 1979
-17- 1JS NFARENT (PNAME)
Definition; Returns in PNAhME the full Process nameof the Parent of the calling Process.
Implementation: Copies it from the Proper fieldin the calling user's PCB.
MSEfI' (P'JAMEi IONBR, LNG, MSGADDR)Definition: Sends a message to process PNAME; the
message is taken from a buffer of length LN3starting at address MSGADDR. The IONBR is aninteser which matches the IONBR in the MRECVreauest bv the target process.
Implementatiorn See section 3 4 (Messag Manager).-
~MRECV tIONBR, LNG, MSGADDR> )
° Defin :tior,* Sets up to receive a message of 7,h - starting at address MSGAEDR.
~The calling Process waits until the messageis received. Upon return? the LNG field will
~~~contain the actual~ lergth of the message - -{ received.
imleaentation: See section 3.4 (Message Manager).
I,
It R
Mlarch 30Y 19/9
. . .._
- 18 -
i A. essage daoaaemerit
The message mtanager is the heart of the kernel. It is
-comarised of the main kernel Process and a set of subrou- -
tines for manipulating messages.
Each active message in the node is represented and
mansged using art IO Control Block (IOB) with the following
eije je ' link :ointer :-->used to link IOB into aueuesI _------------------------
owner iOB list link --:link for a Process's list of------------------ active !OBs
owner's local name---------------------------------
i co.trol br I-->used to match incoming messages-------- - with the ProPer MRECV reaues-tI/!O statUs :-->status of IO? IN vs OUT,------ - and 'WAITIN6, BUSYIor COMPLETE-I , action code -- >encodes what msg manager should-
The------- the--O-an--t--- do when /O co thletes-4r -t-o d-r;nmie .sA b. -. NULL if no di.n..dc buffer used
fig bodV aidress
Smessa~e !en:Etha
oe hder for message -->see communicatnoe manager
" T~his= block contains_ Ell the, irfor,,a~iorn needed to-keep track -
t ~of and transfer a messag-e...
The use of the IOB and the operation of ths message-"
,ar, =s~er is best shown bw tracing the Path 6f a message from
~one user Process to another.
March 30? 1Q79
- - - - -- - - -- = ~I-~~ ~'~'Matz_
- -- - - --
I rdN __ , mi I.n~.It ZN I-
P rocess --- -- -- -- -- ACTTOjQ
* * I w4k IIi A Wa' 1
ItI
Ii user
kernelservice - - output-a". ! --- slot
-i -- driver
The above *ipa S, ilIustrlates the control flow for Ir -e r -bv-step*
messase -n-e nod. Stem
[ i i -- The kernel call routine, acting or, behal of the user,
uses calls to sessae manaseent subroutines to obtaina nd ij ir a rew IOB
2-.;B Je S is f iled in, it is plaCed on the IOOUTQ,1 F I F O oueue of output messages waiting to be transwit t,., Th.e kernel routine then Puts the user to- sleep. -
The message is Picked up bs a device driver see-section *. , Lommunications manasement) and transmi-tted.
The IO is then Placed in ACTIONQ, the main kernelprocess ' Queue of work to be done.
-I, The main lernel process retrieves the ICT from theACIIO -and, quided bv the ACTION CODE filled in bt step--l-,wkes-u the user.
5 The user Process wakes up, still executing-in the kernelservice routine. This routine retrieves anv statu-it-
_ nedE from the 1OB, then releases the IOB and returns tothe user.-
j March 30, 1979
o- L- M 1 I
A slihti different seeuence occurs in the receiving
n~rode
I
el ---i-ms nca mrt ---<--:-
Process #--- ACTION(
wakeI- user - -
kerne --service message ----------- > input
LS± islot -IPCB --- ---F' - driver
SOBiI t' te-rsei1 --+ fi1d'ac
jI - TheKernel ca!! routine, acting on behalf of the user.*ec l tmessace manaaement subroutines to obtainend ::±l :n a ne=w 1B.
'2 'i further sction is taken directly with the IOB. It ileft "hansins' in the user's list of active lOBs.
Tekernel routine Put-s t1he user to sleep.
i97
rMarch 30- 1r9
1 *3 -When a nessage Comes into the node? i has a h-Eder1Which contains S~ aet pr-ocess iname and an 1-0 number
(see section 3.45, communications, man9!easantV. Th eroU:tlne PInDIOBP --ses tne h-ash table t4o t~-4 he tartgetit ocess's P3arjd then the TlB with thje --a,-Cht1 r
number. A-Le the message traensmission is iihdIL helO :s~ice i ACi~4O te q-ain kernel p-rocess's2~ueue of tor;, 4 be Qdne.
4-the m-ain kernel process retlrieves th;e HB f ro* the ATOG
and- guided b~e the CYON CODE1' filled in bu step Ir wakes-
- ~ ~ - -heser-- r~ wakes upy still executing in the kernel- -
rhs outine retrieves anu ctatus -itj
r~ees 7ra ne Bp he releasec 3jc 1M and ret.urA-ns to
a.-n- to 1ion'no at comple~t ed 10B's to see what -
ii- -pl:m- Sh- untin M. are =--c reces
1 rmre :ervIce- -eQ~e:s5 t roa 4 ther nodes. When a &---sageI
r4ontlrn-n sur-'n a reaet is rec-eivedr action neede toj1.1sa~st te -~eo~ are ldne. A replY aqessate which co-9
retu-rn-~ar--o is then Prepared and sent.- - 4
Ii Two reso -euects are p-rovided? create new processJ
sn a~jd start- Process. he- fe-mats o f the sessamse bo3dies a-.--
-------------- - -------ii - r~flProcess prnoc To nh-I- j --
code *Priority Istart rep-is to Idrs
aK IMarh 30v 1970
0- 22
REPLY TO REMOTE CREATE
1retouest 1full n~ame1 code 1 f4. o
=-1 1createdV REMOTE STARTrenuest 1full IC ribr to
code 1 Process 1replv toi 2 namre
REPLY TO REMOTE START
reauest'---i code
Of coumrse use is also made of if ormat ion in the rnessagie
headery so that data is rnot duplicated in the message bodv#
The resulting~ (simplified) cvcle for the main ker~nel
Process is
B!Do foreverGet IOB from act ion aue-icIf it's a remote reouest
Dlo the reciuested actionh Reuse the, lOB to send replvelse
Do cotw-4.etion actions encoded in lOB(awaken usery release IOBP etc)
The routines to obtain arid release lOBs and d,-riarriC
aijcssa:Ee buffers are also considered P-art of the messa~ge
man~age r These routines ere straightforward and will riot be
discussed hare.
March 30? 1979
tk_ Comuuricatias Oana~smeit
As F-oirited out in section 2,2P the controller appears
to the CF'U as, a number of independent devices called
'slots*. Each slot is controlled throuh a section- of
EN-O-eSSGEd bis aedfndietesau ye
comn Threaetwo set curnt slot rronst foitrptan o
sete o bu~te 1thesfer slt bete in adrectoracces' fshioadWreseRED commn btiso, h so
trners? dte twit oRED out of MIAT thbre defsed in -thej
comand FE te AIRS iel 4 w For eac ERRte trNs-FerFFRed -and~
STR~~NSFESADES bits anredened and the s'ttu COUT i e# c
me hred arAw eso lt*oe e o nu n n
ac essealonditions a the trDcmansfetri onrtithe slt
metpiend.trd ED-FBFE)
7 T
- The end of messa! e is found (input onlv),
3Mrch 09, 1971
-= - ~ -t - ~ - ________ 4A
V_
1-24-When one of these occurst the fc llowing step-s are Perf ormed
bw the controlle,#
1. The comman~d bvte is cleared.
2t The a,-ropriate status b--e is turned ctis
I 3. An interrup't it: -aererated*
4. The slot waits until a new command bit is turned on.-Ii ince a single messasie mav be composed of' _jl1ti ie
buffers ins locsal mermorvy i-1 will need to be transmittediseveral Parts. Conseauertlvy tne communications, chnrnel
must be told ezlct where one message ends and the next A
~ L beins. Tis i-: the function of the TERMINATE command oni~
output slot"i~ causes the termination of' the current mes-
sa:9e. The nex<t ti'ansfer operation is then interp'reted 'asrIthe be:9innirig of' a rnew trotssa:9e# On an inp~ut slott thS-TER_-'
r7 MINATE command causes +.he remainder of the current,, messageI Ito be flushed.Anv aessae thas tle standard- format
J-- message message
targetIta March1 10, 1979re ouc
nod 1 rocss1 i noe Pocs-~:
-25-
-7N
Of course, the 'target node number' field is used bw the
communication hardware to route the mcssae-
.1 The slots are controlled bv a set of drivers (iiPy-e-
mented as Processes), one for each slot. The output drivers
are identical, sharing the same code and having separateI
local data stacks. The same is true of the input drivers-.--- -14
The out.--ut drivers take their work off a common FIFO --
aueue of messages (more strictly, IOBs) waiting to be sent
The header and bod for a message are transmitted ast
separate buffers. So the logEic for an output drive is**-. ..-
Do foreverGet a message from the output QueueSet up slot to output header- ~~~i,sue READY comma.,d, end w ait fcr interrupt . .
Set up slot to output message bodvissue READY command and wait for interrupt -Issue TERMINATE command and wait for interrupt.Send IOB to message mann er
The logic ror er, iriput driver is a little more compli-
cated. The message header must be read in before the-mes-_--
sage canr be identified and the Proper input buefr can e- -A
selected. Conseeuently= a dedicated header area is reserved-
fo each input slot. After the header is read- in -the .
correct IOB to receive the message must be identified (sen-
section 3.4 on the messee manager)# Once this is done. the--
rest is strai:htforward.
March 30Y 1979
_2_- ___ -,, ... . -- - -
-26-
Do foreverset up slot to read into header area
arnd issue READY commandwait for interruptlocate matchings IOB
<or create one if target is kernel)Icopy header into lOB U
set up slot to read into mnessage bufferarid issue READY command
? wait for interrupt
send IOB to message managerIAfter both input arid output operations, the message IODis sent back to the message handler for anv closing actions
that mav be reauired.
FI
2n
Mac 0Y17
- 27 -
A . IHE EkiULAIION &DRA
4.1, X-Iree Uodes as UVIX Processes
in order to test and debusl the node kerrnel some method
of runnir, it on evistin hardware is needed. At this
university, the most convenient way to do this is to run an
of emulation on the UNIX s.tstem. Hbwever, the emulation
cannot be done as a simple UNIX Program. Two levels of
Parallel Processing are needed:
(1) The X-tree .)as more than one node. A wav is needed to
model the simultaneous execution of the X-nodes and the
communication between them,
(2) The k.ernel of the X-node, together with the user-
Processes running ort that node, represent a set of con-
Icurrent subr'rocesses executin5 within the node.The two ty-:es of Parallelism are different in one ver-9
E important respect! interprocess communication,. The X-nodes --
have ro common local memory through which to communiate .IThe kernel subprocesse_-? on the other hand? rely heavils on
memorY structures that are in the local node -and are,- avail---
able to all subprocesses at that node.
This observation leads to a relatively straightforward
emulatior, technieue# Each X-node is modeled by a UNIX Pro-
cess and thev will transmit messages using UNIX 'ipesSo.
Modeling of the kernel subPTocesses within the node will be
ORMarch 301 1979
discussed ir. section !IIB.
It would be Possible to set up the P'ipes between the
UNIX Processes so that thev form a binarv tree analogous to
the X-tree topolo:'s. However, the Point of this exercise is
to emulate the runnins of the X-node kernel, not the commun-
ications links. An alternati-ve, which gre'atl- reduces the- Iamount of initerprocess data flow, is to define a single Pipe
into esch Process. Ar, message is sent from one Process to
another bv simply writing into the input Pipe for the target
r.ode. The emuiation network topologv is then fullv con-
nected and looks like:*
------- >Pipe to node Inode ----------- >Pie to node 2
-------- >Pipe to node ni1 1
1 - >Pipe to node n --
node ---------- pipe to node 2Pipe -------------- 1 n
----- >Pipe to nodp n
The simple use of Pipes does not solve A-l of the com-munications Problems. Each node should be continuouslvy
wo 'king on the Jobs it has to do, and suspend such work on!v-
when there is a message on the Pipe to be read in+ Unfor--
tunately, a read operation or, ar empty UNIX Pipe suspendZ2
the entire Process until some data is Placed in the Pipe bv
March 30, 1979
A- _ .. - -
- 29-
anothier Process. Conseauantlv, some other mechanism is
This Problem can be solved in Part through the use of
UNIX 'kill' signals (see aPpendix). The name 'kill' isH somewhat misleading since these signals car; be 'caught' bv
the Process receivins the signal. To accomPlish this, the
Process to be siAnalled Perform s the svsteirt call
tin catch 0;signal (sinal-number, catch);
and contir-ues to execute its other tasks.
Then? when another7 Process sends that signal-number -to
the Process with the svstem call
kill (process-number, signal-number),
the funztion catch() will be as-n.-hronously called in the
sigmnalled Process. This call is like Fnv other in that oh
exit from catch0, the signalled Process will continue with
the code that was being executed when the 'k.l" signal was
~received.
One more aspect of catching sisnals is verv important.
Once a sign~al is ca,-ght- the 'sign~al' sistem call muSt --be
re-issued to catch the next signsi. Our communication st ;s-
+e , code that, looks like
-I
March 30, 1979
-- t=-
-30-
-to send message*write into Pipesend signal (s-stem call 'kill')
to receive messageinitialize with
'signal (signal-number, catch)'
function CATCH:awaken subprocess to read Pipe
return
subp recess INF'UT:Sdc forever
read and Process messagere-issue 'signal' system call
g9o back to sleep
This i still not the final solution. Since any raumber
of Processes carn write into the Pipe at virtulall the same
instant, a dangerous condition occurs. If two Frocesses send-$Imessages into the Pipe in auick succession, the receivihni!
Process will not be able to re-issue the signal 'catch1
efore the second sisnal arrives. If this happens, UNIX
will abort the receiving process? which is clearly unacceit-
able.j
To solve this Proble.m, the X-tpee node is split into Jtwo UNIX Precesses. Th-e prisarv one, called PR0CY does mostI
I of' the work and operates as before. However? other
processes dc not write directly into its Pipe. instead, an
i, terveninS grocess (called COMM) receives -messages from
other nodes and sends them to the PROC Process one at a time
using a simple hand-shaking Protocol:
t --
Mrch 30, 1?79
il Ail N -MLEOW"j
N- - 31 --
-- -> PROC sets to catch signal from COMM IPROC signals COMM that it is readvi Mi+ "for mes sage
COMM Puts message irom ites pipeCOMM Puts message into Private Pipe to PRO'
and sends signal to PROCpROC receives signal from COMM then
reads and Processes message I
Nodes which send messages are now relieved of the
necessity to send signals after writing a message into the
Pipe for another node. The COMM Process can afford to wait
when it reads an emtv Pipe.
'T, resuiti-ri f-nal topology is A
i, trpt
,>ip to COMM I-7 COMM PROC :--->Pipe to COMM 2P1-- I _ .,>*= + : -- i e - > I I +.
---- >Pipe to COMM.-n
signal
intrpt------- - S ig I -----i-
* , - ' , I, _*.- -~ =_M
I I I .: -- >Pipe -to COMM-I-.... M : , PROC -- >Pipe to COIM-2 -
P] p.e ., n :--pipe ---. >: n , , .... A;
----------- -- n-------1 )* - 4,* .. ..- - - I ,~ I----i. toA rDAMr -
read. -signal - - -
On-y one Small detail Still needs attention- It is- notciuaren.eed tha. data from a Pipe will be read out- in 'he
same ur:its thet the,. were written in. Messases will not be
shuffledt but thev mav be received more than one at a-ti,e..-
March 30, 197?
When a Pip'e is reads all the aiessa 4es currentlv in the Pip'e
aereturned bv that sirig1e read# Hence, we musst reserve a
special rncssa~ie sep'arator bvte. The COMM Process searches
for this separator bvte and splits off' sins~le mressages to be
sent to the PROC P'rocess.~ Thisy of course will riot be
3, necessarv in X-tree itself- sinice the end-of-mressage will be
trarismittei usin~g eai extra bit. 1
I
I4
Iac;3Y107RN, NO I
A.2. Subamocesses and Ibeim Sucbronzalioa
The use of multiple UNIX" Processes 4Ls a satisfactorw
way to emulate the concurrent operation of the X-tpee nodes.
However, this technioue will not work for modalini the
coroutines running~ on a single node. Separate UNIX
Processes do not share anv global address space; the corou-Utines in a node rels heavilv on such a global data space for-,
Communication. Implementing such a data space as a diskIi file w.o1ci bc- toth awkward arnd inefficient.
This difficulty imp!Jes that multiple suhr-rozssses -must
ismhw b ffak-ed' wit-in a s'ngfle UNIX process+ The UNIX
svsteim offers no direct solution t1o this r-roblem. Fdr- Itunatey however3, software to do just that wsdvled as
Part of the To-- Operatinct Svsteif I/) seatUC rkelew to
teach operati4n-- svstem Principles. This code Ias- been
coPied and used in the X-tree kernel 'emulator. The - a ck 44 6:is briefly descri-bed below.
A subprocess is defined as an independent e x e butio
streari toc-:ether with its own separate local data stack. Al1
externjAl data structures and variables are shared among allI
the subprocesses# To implem~ent this concePt, a series o6f
data stack storage areas are allocated, one for each subprd-
cess. At anv moment, the data stack for the-cu-rrentIw--I
active subprocess is found in tlhe normal stack locat-ion-
ff fgrowinE down frog, ad-dress 0177777). Tgo activate a dif ;
ferent subp-ocess, the dlatc stack for the- outgoihnSv IMarch 707 1979
subrocess is copied into its stack save area, The data
stack for the new subprocess is is then co.ied in frs: its
save area.
hdr ! hdr hd r hdr l - r :
:StB s 'N'. i s ta ck s t stEk stack 1 stacks av* e s s=ve ; ave save save
fo r fo- for 'N; for forub ,br s subr r sub. th r- r -ibr r subpr
* I
te 2: S t e r 1 II
ioad new l = eold-s E- C. ; stack
. a a.r
.I _e
S-e 2:Ste 1
it is iorta.,t to note that t, oni --riv.--te storae-I eoei tc a subprocess aS in its local data stack. A"l
II Lode and external or E iobal -ariables are shared- between
then. A:n needed snehronizatior, must be andled expli-
' ub~rocesses are created in a manner analosous to the
torkir5 of UNIX ProcEses. The val I
I int PrioritvsPfork (s'ricritw)
allocates a new data stack save a:-ea and stores a cop o f
March 30 ' -:.m
31
the data-- stack in it* No new data stack islo-aded ovep the
old one- ence thor-a are now two su'bproeesses which e-xecute
frm !._=same POInt. rho.,-;WSW to distir.u=sh the two i
b,2 the be returned- ft-os% "he sp 9 ok f uncticn the Child
receives the value 0 and the PC-rent receivles t*ne clu-~eI
( it' i-.7 (fok(3 3 0) 0h~ 3
wil -reate child subprocess which will enter -the -function
cn...e= T~Parent sut.-rocess will! contisrue uitt th neit-
ctzn crni scbprov-esses Is corrl-
onI h o uh 5 1e -e o~f sesano--,?ith -trh P -nd V o -
t -exe n' ts d£-=4). -he operatio areo~:: - -
known -=ano w I n-tbe ceJsc_-r;b. r=e. ±n tNsaslen-
Ito n ia P or-e e reresentled Cnia -vlu and a linked-i usj- 4 s ub PrQ~t~ ar w hEe Wa~tanS -tor the Sesapn-o re.
mer-rhores r ~'se v the subhrocessces of the kernel->
e mulz I . a s-- c v two stI. --ec. -n the first stvlew_ a-suorooc oe~-te o~ 'crk psckets taken from aTl FIO ueue.
V-ie basic cuole frsuch a -r'sbpro-cess is --
- rse t a- wo rkL packlet ft" OR' -z
ro Ce s s wor:k 2packet
As patof the o~veration 's-et work Packet', a 'P' operationn--
elmetsin thV uue 'th ue : m th .e sulbprn-
-a rc h ."5 1a4i_____
j -~ 36-
j cess the.-t ,aits until r, other subprocess puts ar, element Ji'nto the Queue, The slot output driverYs, for example,
operate this wav# Thev take their wor. from a aueue(IOOUTO)
of I/0 control blocks for messases which are waiting to be
sent out.
The second stle of ,se is seneral' cslled Private
semar-hoTres, A Private semapthore is- Per.-,artent!v assi!ned to
a ParticUlr subprocess. When the subprocess ,,:j't wait for
some reason , it does a F operatiorn or, its Private semaphore+
It then stavs asleep until some other subpnrocess wares it up
bv doin3 a V or, its (the sleepir sub.rocess' s semahore
- o2One examle of this stvle of sema-hore use is the Pro-"
cess which 'eads messa ies from the i'e. It is called INF-
DIS;l -which stands for iNPut rjTS atcher It waits or,
P private semaphore celled IOINT. -he si rnal from the COV
process T'norces the e.:ecution jf the catch routine which per-
forms a V or 1OINT- th.us wa.ins the IOINT subprocess.
The subprocesses for the kernel and hardware emulation
were writter on top- of' these s,r,chronization Pr.imitives,
In order to keep the kernel code separate from the subr ro-
ces_ ,lementation code, almost no chan ges were mrad in
cor- *ir the subprocess =,ackae from the Tov Operatinr Svs-
tem.l
CI One cherse wa needed-. however- because the P and V
operat ios ust be .ndivisible in order to be valid. In the
March 30, 1979
TOr Geraftinsi S,-stea, there is no possibilitV of -s real
S n r! ' onao u s in~terrupt from outside the s-ro~ramyi so no sp'e-
c:a1 m-*?sures ha-ve to be ta-Len. This is not, the~ case ina thle
I-. 'A-t- k.~ .eriiel eraulatocr. The 4COM p'roL-iss i mav serld the mesa-5
sase in r-ipej i rite rru-t- at arty ti aim zs d es cTi b ed above?
this wjill cause ar j m err-zii ciat e call to a va-broui-ine which
wea:es up Lh NTL-ISF' -rocess. If this n t e: r u.-t arrives 0
while a low Priority siub.;;rocess is doing a For V operatioa,-47
that uperatiorau would be suaspended ini the midodle anid an error
miay i'es.tj It
ITo lke-or- thls fro.-1i har-.enrtins it is desirable to disablea
Ithe interrupts at the sta-t of' a P or V o,-e-rstioe arnd i'eer-
Iable ialerrupts a t th.- en.L of the initerr-upt. The cyerhead A
a -If 2cta -1 d is abl ni th- '.riterr!upt would be unacceptably
hgsince iLt would involve a cou'aplicated s 4. Ia I protocol
t.e er, 4the F'POCl arid COMM r-ro'esses. Instead? the -interrur-t
is rceve-J, but the awkeriinz4 of the ITDJISF sjbprocesS isI ostporfed.J
Ait en'try to a P' or V opeTratioa a f'las is set to indi-
cate that i: 1 Lterrur-tLs are disabled. The CAC ;-outine must
check this flas when an inaterrupt, occurs; if dis-abledy the M
n %e rru-pt must be noted, but INTDIS-P cannot be awakened.
Theri, jaust bef'ore exit from; the P or V rnperatioa, the inzter~-
Irup'ts are Tsen a b1e d arnd if an interrur-t occurred in~ the.,m_ ~eantimae- INTD:SF must '--e a-wak.ened.
The logic for this thenr looks lKe
IN;Mac-0 1 -9-4 _
1~ 38-
i i , subrocess INTDIISF':
loop foreverset to catch initerrupt with CATCH().s i srn aI COMMW readv for irn1errupt
r'ead arnd process m~esa ge
interrupt routine CATCH:if (itti" itte RE
eleVION)reur.i
P prain
Fnpds ;HLE
doIeit4 r
V
Mac 0717
A.3. Emulated Communicatir _ d amdwame
The co-muri cations : l between the kernel software
and the communications cr. "oiler waa discussed in detail in
T he-ter 2. .Hew is the .Leractio7i between the slot device
drivers and the charnel emulateo so that messa_ es can be
sent thou:.h the UNIX Pipes?
The emulation of sr output slot is -elatiyel- straight-
forward. Each time a device driver Puts a new command in
'he SLOT COMMAND BYTE, it calls the OUTCOMM subroutine.
OUT C-MM maintains a set of mressage assemblv areas, one for
each slot. When ralled- its functions are simple*
if command is READY FOR, TRANS'FER:.take the bytes indicated by the ADDRESSend COUNT fields and add them to the
12 "Iend of the -Rescaee- increment the ADDRESS field by the COUNT
ind set the COUNT to zeroPlce END OF BUFFER irn the STATUS fieldand return~
if command .;5 TERMINATE*Put ti- MESSAGE SEPARATOR byte at the endof the messase
write the messase to the aPproPriate Pipeclear the messa ge areaPlace END OF MESSAGE in the STATUS fieldI rand return
The INTERRUPT ADDRESS field in tne slot control buffer
is riot used for the slot output emulation, The subroutine
return address Performs that function.
The emulation of the input slot cor.troller cannot be
done with a simple subroutine call. The output slot is
March :0, 197g
-- 40-
driven bv events occurrinE inside the kernel software. The
input slot, on the other handy is drivenr Primaril bv exter-
ral events- namel. the presence of bytes and messages on the
iriFut line.
The emulatior of the input slots is Performed b- the
subprocess INP'DISF, which has alreadw beer, mentioned in sec-
tion A of this cha.pter. INF'ISP is implemented as a subpro-
cess which is awakened whenever- there is a message available I
nr the input Piae After reedin!9 the message from the Pipe 4
i
INF'DISF' then eulates the anPUt slot controller to trarsfev t
the sot into ae kernal. 'ha
o Usiwne the ADDRESS aed COUNT fields of the selected
slot INF'ISF' transfer- btes frogo t mesate inot
apropriate area in the no-de. Wher; Brn event, such as BUFFER ZA
FILLED or END OF MESSAGE, is reached, TNPIDISF' awakens the
appropriate slot driver so that it car, respond to the event)
The slot Jri%-es aTe run at a hi:5her Prioritv than I NF'DISP,
so when awa.ened the e execiute immeditelv.A
When TNFPBTSP mase4 control beck., it means that the irput
4 driver has finished -rocessin:5 the last event. INPDISP then
continues to transfer more data or waits for another mes-
sae. Hence the logic for INF'DISF' is*
March 30, 1979
- 41 -
-41-
4: do fore.'erWait for next messasee
Rerd in messageWhile more messa e remains
Use ADDRESS and COUNT fields to transferbvtes from the message
Adjust ADDRESS and COUNT fieldsIf more messase remains,
Set STATUS = END OF BUFFERAwaken slot driver
Set STATUS = END OF MESSAGEAwaken slot driver
This results in a beck-and-forth action between the kernel
slot driver and the INPDISP' Process. INPDISP Senerates ant
event and awakens the driver. The driver reacts to the
event and then goes back to sleeP, allowinS INPDISP to con-
tinue. It is i.mportant that the drive!, subproL-ess have
hihep prioritV than INFDISP. If INPDISP ha'd the hiiher
P-riority, it would continue executinS until it waited for
the next messae.
I Here a5_:in the INTERRUPT ADDRESS field of the slot con-
trol erea is not used exP'licitlv. That function is handled
by the suberccess packa:e, hich knows at what address to
conrtirnue executin_ the driver when it wakes u. Instead,
the spC&c of the T1TERRUPT ADDRESS field is used to store
the address olf the Private semnaPhore which is used to wake
up the driver.
March 30f 1979
--- - - IA
17 77' - I
To e~rontrate the k'ernel emulation Prosramv smlFuse i-rosari was coDded and executed. The Program consisted
o f three 1.iser rrocesses III UER rint 'Ucc-de 0 executiri on node X. "rete a process on node 1 to execute USER 1.tart th- 'ness just created.
Wait for a message,in that -,.:§sae was received ariddisplav t.he msssage,
CrSeate a Prcs onnd_ t xct USER 2.j
S1a ~nd messsge 'It works!' to Parent Process.
Ex ;t t~ 'IThe 'kernel calIls' made to start Processes and send messa~ges
I - are de~tailed in section 3.3.
her terr -m~tr is startedp it sets up the tree anid
starts the kernel in each node? th!en waits for a commsrand
LI ro!7 the terminl The terminl -iperator must enter coim-
mamv~ to reale and start the fi; -st user Process. Dtie
I instructions are included in aperidix D.,
The session f~or runninc_ the simplie Proz~ram above is
rerduced beicw. O~erator commrands -3zre soni
Miarch 3-1" 1979
-43-
St * -arentheses (the Parentheses are not present in the actual
session).
SESSION COMMENTS -
: ?. xtree
invoke the emulatorcommand cret e 3 S 0)
create Process to run codese-sment n on node 3 withPriority 5
-Prces crated on node 3, nafted 3 1 *i : : " Frocess 3 - atare or oe
s tart the Process Just created] ~~~Ucode 0eeutn ,noe.
t*- Process create: on node I- named 1 1 **** Process i 1 stted on node 1Ue:uodE 1 execut.,ng or: node i4 1.
:C Prccess t-- o d r:aeoiec 2 i * d*k.* Process 2 s started on nodo 2 Z:ICede I about to Lend ms .
Msa recei ed by Ucode w was-. I :t works-
1 ** Process nte ode I ***Ucode 2 executirg on node 2.
* -* Process 2 1 terminated- rode 2 W*
The messees braceted by "***" are informational messages
prrovided by the I ernel The othe messages were Printed _v
the user -oram.
iote thEt USER 2 didn't actually execute until after
USER 0 ad USER I had finished. Since UNIX actuallu runs
S ol one process at a time, there is no real Parallelis sat;
on,! one node at a time car run. Further, close examinatior,
of the user Progra , reveals thiat USER I does not wait forU USER 2 to finish execution! but rather to Just start run-
nine . Hence, the seouence above is a correct one.
March 30, 197?
- 44 -
in short, this demonstration shows that the kernel
desi-n is loeic ll correct and that the e ution tech-
niues escr4 bed herein actuall3 work. However, the kerne]
CuT, cticns an this version are extremelv limited and much
more work remai.ns to be done before it reaches its final
form,.
jhe -ri.ar' success of fhe kernel desisn is its fiexi-
Ii. it rebtivels sa.Fle and easy to modify, con-
sistins essenrti ' of a set of work stations (Processes and
dqvice d. r rive r, wih retri e-ve and Process work Packets
S a -LI New feet-ures, such -s those discussed irn
section 5.4 C art e aiF- Iemented in some cases b- sim l
r-new orPtios in existir: p-r-ocesses or bv addirg new
"-i s ecial 'ur-ose mrocsaessesa
A
,ME
.arch 30, !979
ir = =
5-2. The Attemaied Use of m a DUL-,
u-i 78? , Heroi-1d Roberts com.-Ieted an evaluation of'
t te MODLILA 1 an:E'ja:e UP7IlJ- He concluded that MODULA was
viable 1-n:Eusage for s,=stemrs ?rrOiamir.g in tihe X-tree rpro-
Ject. As a result of his studv, it was tertativel-Y decided
tht+ OUi was to be the P'r-imary& Pro:Erarrtmip.: lansfua~ge for
X-tpee.
.owevenm so-Tr- -'roblems withn thre lsnsuage were reco-
-a ied. ~wo defiacier-cies were es.-eci.ally_ imp-ortant to thej developmient of, the kternel.
The The k of Po~nters forces ro-ra,,s to be written
jsirc-s -_rav ndex .oain TT, reuls inr s 0.71wCat
iriefflicient cod and o casiornaliy awkward source text.
(2 I~thoush MODU4 Provides for the explicit exrpression of
q, t tIP~E -recesses and svnchponizatic-ti it was irnple-
mented l onv bere n rdeniyins: operatins; svsteri,
IFiP an r~ d'
Asasul oiP hese difficulties, the kernel was to be
deindui8teMDL a)9ag n then, translated to C
1"-h,"r ~'b 1 eediS_-o, e which led eventually to
r; doo i n: MW altosether for the kerne.
- __ The first -r~en ufced djuring the design of the
interface to the cc.siuricatiOns co.ntrollen. A Ith ou ih J.t is
arch 370, 17-
-46
actuail!_ a sirs_ le device7 it acts like a multile rnumber of
identical devices S lots). One strai.ghtforward wav to
interface tv si&,c- a device is to have a different driver for
each slot. This leads to reiativel-= simple and understand-
able code since the aLor-.hms do not have to worrv about
hardnirn mrijlti P-le slots simultareousl. B.ut this aP~r-o'ech
is oil -ractical if the device drivers car! share ommon
Code ar.P each Can ha-* a ppiV3te pointer to the control area
fO its slot if this is rot iossible, the amiount of memorv
space r, eeJed 'or duP i cated code for' all the drivers would
be Prohibitive-
Urfortunatel this is imossible in MODULA. The
a=ddresses of device resisters in device drivers must be
dceclred S corstants an ca inot t- Passed as -arameters to
he drier ,.her: 4t -s ir.itiated.
The secon.d Probem -rose when the al-orithms for inter-
getin, kernel fiesssse= wc written. When a messa-e is
receieo, its contents are unknown. it is oniy after the
fjrst word (REQUEST T V) o the mr.essage has been eaminied
that the -crmat of the muessage is known, However, it is now
impossible to break the messaEe down into its component
=arts because O.UL. is strorl-l± tved and there 'is no such
thir, as a variat .ecord, it is even impossible to write a
r~cn-hODULA routine to ac-complish this since there is no we-s
- ih a t i-
The oniv alternative in MODULA is t6 define all of the
Marcb 0, '0 79
--- - ---- _ - .. . ... ...
Js b q essages such that n>L I.temsc &f i.dnt±:ca type lto
'1 ci r~ ive POS2ton *. hs~ mvnsase, Unus ed
fields in eacin mssa=!gr WOUJOd nave to Lbe till-ed with duminY
i nf ornmati on . This is no wa,: to minimiz-e the coinmun-,cations
I bndidh eeded bv the = systenn-
'Irlne final Pro-blem7. Is az result of' the metho of Process
syvn cnhon izatlon P r ov i ed bt- NODULA. ?lutz,al exclusiont is
red bS n ntrcemodui&"! a set- of sc~urce text i n
which onls o ' - ess mav be active ;t1 a time. At first -
~lacerthi sea~ suficet u it leds to mu ti rle
cop1.ecL of. the san-e code.IIidr;-, varaous elees 0.
c co-no bIo cks inthe kern el 11 of the routinses needed to
- AMsr*:iI at-e t e s:Je- Sre the sante. to atchieve mbutual
eXCi m-an 0!h: 0outines s'? en =r-close d in an interface-
- q.;F. -l5wu~ as rocess witc h wants to use
nuceA o ,a~ :fa r-other e s sro- s u s~a cue B. Th-ere
is no : av to ; revent t?=iis except -to provided sepa=rate inter-
fae odule s- he n e cuaicateJ C o de P f or ea ch !e ue.
-f' cou:rs- i s no;-tihout its own- problems. It gives -
o n> li sri ce to0 abstract-ons and data hiding and 1=ro-VVIOC no e'i F-Ic m e cha nisms for multi~cie sub-rbcesses and
£yahoazto. But at least the lang'uage is.Fpowerfui
enoius to a"I ow thecm tvpes of' c-=t ructins necessary for the
kreina relative> eff'i c ien t fashion
',larh 3.. 1?7
crocesses was discuss=a -. The dcisxlon not to roodjify thIsi s
pack-age dld nave scene unfortunate re; ercus=ions ir: the em-ula-I
The L irtzsa otb u du?1 Stior of son~ structure.
T he RUUcSE =,rocessas are r-esresenteC s h s-truc-tures a
the sus'ces c-ec he PCB de-fire iitek-nei
MS re~ltsome fle-1i.s tn he P05Z are not actually~ usedIZ!j s-z th4 ol be 4 h a re kept in thUe subr-ro-
j ces S -EC s s :rErto .are not m-rle vsbittl outside it. While;'
S a n e t ! G =- - *---II -~~a -. o j.--ol, - wo ld e ai . = step
towarnd s.-Iv ns tne -w- 'F aocg -r=aoeooeow
One s61CC -' 7-_ ofl- P~rev- F3a_-kCa is thta Pro-1 ce ss can sc z le: O-=-'-' a r o-eratzon on 2 seine-
---o~.Tere Is nlo dzre c wa S c-r c-ne -roces- to Put
=-46 her 7 -_)ce S 3see - to serfors anv otherkido
contol. Ms Bbil -t- woud b-e convenin so"atoe--
ttionl IKe A PORT P-RO'1C ES or ."A' T PROCESS could be imwl-e-
Av--e c" oblem ca-used bs- the sub-r-ocec= package h-as to
I do w it se _l, - receiwv-ir:- mess-es 1. h.e user -dat~a
srlov-e nc ,r,0 out of t -,v dL ~=c ti
March
sa ck pne.ttSrI t -u I the c'~ s 3Ct ± S- Z ife
"f te e-ser aessaale L.=jfer 4s stlored in the 1
block Ed - slot controller, te datea wlil be
trfstre to Or ro0m tnle -at sLK of the totroller, not
of the se-
:SS5e Sthr-ous5h a LN=F-naathc ki.ernel lbutter-4 Thus the user snce
(I u~~ser suo'ces
Iii=ENO
=11z rI
50-
'-. rulume Iasks
Th a ke rne 3 n .ts r-resert fOMT' Provioes ar ex r eim
limited set of services. Howeverf the desin arnd codir,5 was
done with some more eneral services it, mind. Seve al pos-
sibie ifrrcvemenits a r e scussea be iow
AD'D 'SYNCHR F JS MSSAGES I"' the h present kernel, Y
user Process which attemts to ser,d or receive a messa-Se is
-,-,tonti.!!' ut to sleen- until the t renis issior is com-
mieted. While this ',s suitable for some applications, some
SPI- ic...s needed wherebi a user could issue a read and then,
ontirue ,rocess Jn:s and Periudicall! check to see if a mes-
saSe h~s L.een receivedi. This service would a s o allow the
user to issue multiple read recuests Limultaneousl: (the 10
um ber It. the r:essase heeCer 1: ,d 11OB was included in artici-
Zation o' th i S service,
AM D0 NOE INTER-1,CL. CLOCK A-~ mothod of dela~sini a user
Frocss Por s Peiied period is needcd. The desin of a
clock driver was coniileted in MOUA. but was riot incor-
-orated into the .-re en emulator, (the code is reproduced in
a perdi.." E), The emiulation of a node clock might be accom-
r!ished bv increrreritrj, a coiuter at specified events, such
sa F' _ar:d operatio, ard a0 completion of each idle loo,
PERFORMANCE MEAS.UIREMENT - It rna2 be Possible to irstru- -M
ieit the emiJlator so -that eperimnrts can be Performed to
com-PTre variou- Possible wads of sFlit -"in cormi-'Iex user
II) March 30, 1979
t j. in to ~Tu f e ~roc e ss e s
ADDir PFjf'3 LUG AND MEMhORY MANAGEMET t-I The PrIatrv~r da rfi-.1 ~j~t~wz~A ~ddns~this f'eature is that it will substantisll'V
irese the UN IX resources reciui red b~ the emiulation.9
W4 thout tf- a-rdil- ion, however -no,, real m-rini Pol 3=erfor-
F msrnoe auessureatent. can Lie taken.
EF2R C0F C IN -The P'resen~t i'ernel as-:uaes that allI y105s B a tr, s q, it4ted re Ii abl I code a-iust be added tocdatect :r'v'c.rs ?rid retransrtit mcEssases when necessarv.-
-1,SO~ W TG I AQ -The P'r'osent enmuIator runs on 1 qcrnI: tn FDP 1/ :0 -AX stm Dir~ect trarns,-ortat,4on to VAX
IUN IX is -:ot r-ossitble 5an~ce thEm subprocess ?-Sckasge use-di in
k >eerrujiaei .7a k.e s use of ths_ -abea stack. forala~t on tho
1/70. The dae t on- the- I'AX jisnt the em, ItaaI Iiso -S, Q s C, I the VAX subroutine linka:5e svstemr
~a:es Imploss57le1 to successf'ulle save and restore the
iJata stsc6. 8sis done ont the 11/70#
March 30f, 1979
REF EFRENCE S
C1 E Cofru~ar arzd PF ,--i ~:9 v Oea t r, S!:StearS T Ie on!:
C _ A 2n-' -'sttersony "X-TREE:* A Tree Structured,Iulti;-Proc,-s~ Coffru te 7 Architecture'? Co-f e rernce
2 roeecr~s~ ~Anrnual S,=mFsium ort Cor-uIer Ar'chi-~ec~ue~ 198i 4 44-151
L i3 A Des:=-1n an~d D Ptterson? 'Tihe CorarF ute r ia, a Comn-Fo rlen t poerr op i:tm o Mol 1olithic
M~rr-rcesors? ubuittd t-o CACM' SerL 191-
[42 E Di-tai Cor-erstiri Secueritiai rl se' in E~mco=x, z~nE =Ljaes (F G er: u i, Ped), Y IeademTic Fress
r- 3 T tic-Cearv. 'A cProposal for the Construction of MP- In
Lz _ -'aste's rf-jct er-ot, nivesit ofCali-
fo~rn _sat Sussie, 197
Mrc 30,cto DC979 "7
Global Memorv Object NAME:Inode:. nod.- nmben of leaf at which object
resides
unioue id - ua -nteed 'uniaue within the node
Global meiorV ADDRESS.
object nafre
I offset -- : offset from besirninr s of obJect
'rocess Control Block. (F'CBfl
link fil_'d :-->used for the FREEPCB-- linked listfull -ocs .AE .iesthe Process sloball0
:-------_ loaliorit wrchoritirStatus word (Fsw) P-->irterr ! .rocess status, sulh as. .. .. ... ..st ..t .....o .. condition codes, etc
_ -,a!. ts Word -.- state of the Process: IN-USE,-- -- - - W';ITING-FOR-IO, etcseataphore ;oirlter .-- >used for emulator swnchronization
Pointer ;--- Fointer to the Process's list of- - - - - - - - - ac'ive iOfs
N.'E t a ret
Prosau, counter Global ADDRESS
stck oiterGlobl ARSS
March 30? 197-,
am
§ R0
1/0 onrsI Bl1ock V,10B)
ouc _, e 4in. oirrtar used to R iin- 4.E io a u e u e s
owner~~~~ r, itlnk ->ii flor a rproCeSSI, liSt Of'-- --- --- ---- - active IOBs
1 owner's local. NA~ME
I /0J conitrol rnbr ;-.used to miatch incomiinA gessa~es-------------- wit1h +he Prore- MRECV reeluest
1/O status of:sati 10 No m OUTYarzd WAITINGY BUSY~or COMPLETE
action code -- ernooes what mrs-s maa~aer shnould----- - - - - - --- - do when I/G conm-letesptr to dvrnanic ,ris- bif -,-: NULL n~ro dvnriic buffer used
-,-S bdv add-ress
heaer:fo 1:nisth >see m~essa:Ee formait
ISlot Control Form~al-#
comnmand !status : current IcurrL-It in-terruptI 1 bvte 1 Llte traensir * .t a6.1r E. s sfaddress 1countI- ----------------------I- ------
I4!IV _aA
-$ Standrdr Mes~ase Formast'
hedrb.)-
t . r-, e a ~ge t 10 source sourc.e
numbe r NAM riumiber NA1I~ I e a~ 1- e 1,-IF
RkE M 0 I£CRE A E
I rq-ec-t P;-ocess Prce= TO1 ribr toXo *---: mit -- start rer-11h to
'RPYT -f'EMO~TE CF,,EATE
c 0d e oF r r--I~ -1 :reated
R~EMO1TE STAIRT
iree!uo~t full TQ 0r br toCode P'rocess repl,= to
7 Miarch~ 30? 1979
- - -
1 -4-
REPLY TO REMiOTE START
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FORIK(2) UNIX Prc'-raaiznmerfs Man~ual FORk 2
i ~ .NAMfork s: awri new Process
V . fork(9 DESCRIPTION
Eomk is the onlx wav new Processes sre created.- The new,--Process s core imrasse is a copv of' that of the caller ofThark, The onlv distinction is the fact that the valuereturned in the old (p'aren~t) Process contains the Procest--'1R'-
- of the new (child) Process, while the value return-ad in thecn:ili is 0. Process ID's rang~e from~ I to 30,00, This ~a
0 IsID is used b, waii(2)#
Piles open before the fork are shared- and have a comimoniread-write Poiniter. In ParticuL'rt this i's the -wa-v thatstab'da'd input anid output files are Passed and also hoW
0 Pipes are set up.
SE ALSOV_ wait(2)y exec(2)
DIAGNOSTICSReturns -'i and fails to create a Process if* there is inade'-;4aete swap space the user is not super-user and has too--'meany Processes, or the svstem' s Process table is full. 4 061th;the super-user can take the last Process-table slot*
ASSEMBLER (PDP-11)
-ses fork~ -F(new Process return)(old Process return'v new Process ID in rO)[The return locations in the old and new Process differ'~one word. The C-bit is set in the old Process, if a new P.ro:cess could rnot be created. U3 -
C-1~
Printed 3/30/701i
KILL(2) UNIX Prosiraititer's -Manual KILL(2)
kill -send si~gnel to a Process
eLilltsed tse sisn oteriset this Prcllss rpecticed b th-
Procasse nube n h Se s'sproces or ae list ofsisa
Th edin rad cast nivrsig Pe'trocesses 0r-thsetesmeffetnv usrIohrise tis cal is rcestricte t6th
If tcessroess numb~end sis o the selvi es ttalote
3,Zroi tre if the rocess iskilleds -1radteur is euernue&-i1the process ds odat haiveresam exepti urser tt iidth
user i ot sheuer~ or if theiz~ iproces e not Seei,
(Processe nmav end rO)al totesevs
ssi__ ll;) Villl
DIANOSICAer is reure iftePoesiile;-srtre-th rcs osnthv h aeefcieue Dbde
Ipocs numnter i/n/7 -
kill si!-
-~.--- - =-~ -__ - - __
M ~- ~ ---
IPIE(2) UNIX FPosrarnmer's Mar-ial PIPEM2
SI YNW SIPi-P crles+e) ne~ccs hrmc
F *The 2iae svsten call creates an/IW meChenism called a piv'eiThe f il1e d e sc r i Ptcuirs r et--,urne d cars be used in read snd writeoperations. When the Pipe is written using the descriptor--It i~ides~lJ up to 4056 bvtes of data are bu~f'ered before thewriting Process is susp-ended, A read usir-5 the descri'torfildesEOJ will Pick up the dat.
It --s assumed that af'ter the Pip has been set up two (orinor-a) cooperetin!9 processes (created bv subsectuent Lankcals) will Pass idata through thle Pip~e with nead and wite
Calls.
The Shell has a S!LntEsx to Set LIP - linear arrav of Processesco~sraected bv Ppes.
_N_
Readc'l on an emptv Pipe (no buffered dsta) with on1v oneend tall write file descriptors closed) returns an end-of~file.s
sh(l), readc2)r write(,2)i fork(2)
The function value zero is returned if the Pipe wes createrd;-C2 -1 i f too mrariv files are alreadv oper.. A signal is geri-
crated iP -a write on a Pipe with only ona end is atteri-ted4ii B~~UGS ld cirnrN- -
Should more then 4096 bwtes be necessary in anv Pipe arnorYf)Eloop of Prc-cessesy deadlock will occur. -VAtSSEMBLER (P-."l)1
Printed 3/30/7
I...........
SIGN AL 2) UNIX Programmer's Menual SIGNAL(2) INAME
sigral - catch or ignore signals
SYNOPSIS -
#include <sigra! h>
iDESCRIPTION
A signal is generated b-d some abnormal event,- initiatedeither bv user at a terminal (a-jit, interrupt), bv a Programerror (bus error, etc.), or bv reauest of another Program(-ill). Norrally all sigrals cause termitnation of thereceiving Process, but a signal call allows them either tobe ignored or to cause an interrupt to a specified location#Here is the list of signals with names as in the -include-
[1 -ile.
SIGHUP I hangu-pSIGINT 2 interruptSIGQUIT 3 uit-SIGILL 4* illegal instruction (riot reset when caught) _SIGTRAP 5* trace trap (not reset when caught)SIGIOT 6* IOT instructionSIGEMT 7* EMT instructionSIGFPE 8* floating Point exceptionSIGKILL 9 kill (cannot be caught or ignored)SIGBUS 10* bus errorSIGSEGV 11* segmentation violationSIGSYS 12* bad argument to swstem callSIGPIPE 13 write on a Pipe with ro one to read it-
rSIGALRM 14 alarm clockf SIGTERM 15 software termination sigral
16 unass i ned
The starred signals in the list above cause a core i mge- ifnot caught or ignored.
If furic is SIGJFL- the default action for signal sig is '.
reinstated; this default is termination, sometimes with- . -core image. If fuDc is SIG-IGN the signal 'is- ignored. O t: --
erwise when the signal occurs func will be c~iled wi-th _the' -signal number as argument. A return from °th_ function w4i-'" - -continue the Process at the Point it was interrupted- .E-cePt as indicated, a signal is reset to SIGLDFL ifterbeing caulht. Thus if it is desired to catch ever --such- -signal, the catching routine must issue another sipoa1-c i --- .-
__ When a caught signal occurs during certain tstem cfIi-.the . -
call terminates Prematurely. In Particular this can occur-during a mead-or write(2) on a slow device (like a- termin-abl"
-~~ Printed 3/30/79 -ME
SIGNAL(2) UNIX Programmegr's Manual SIGIJAL(2)
buzt riot a file); arid during~ eause or wait(')* When such asi.~nal occurst the saved user status is arrarnged in, such- awe- that when return from the signal-catchiiS takes plae-?it will appear that the svstei call returned an errorstatus# The user's Program mav theny if it wishes, re-execute the call.
The value of sissaal is the Previous (or initial) value of-furic for the Particular signal#
After -2 fomk(2) the child inherits all signaals# Exec(2-) -
resets all caught signals to default action.I. SEE ALSO
The value (int)-l is returned if the given signal is out of-range+
BUSresett there is no chance to catch it*
The tw~e specification of the routine and its furoc -argume-tA.ape Problemiatical.
4 VAX-il, odd values for Lucic are the same as SIGJG)4#- ~ ASSEMBLtR (PDiP-li)
(signal = 48.)S%_s signal -sig; label(clId label in rO)
If label is 0p default act-ion is reinstated# If label is[I ddt the signal is ignored. Anv other even label specifies
an. address in the Process where an interrupt is simulated.4
An RTI or RTT instruction will return from the interrupt.-Ii NOTES (VAX-il)The following defines the mapping of hardware- traps -to s-i-Anel s*hi Arithemetic traps*
Integer overflow SIGFPtInteg**r division b-s zero SIGFPE-Floating overflow SIGFPE - -
Floating underflow SISFPE - -
FloatingS division bu -zero SIGFPEDecimal division bv zero SIGFPE --
Decimal overflow SIGFF'ESubscripT--range 'SIGFPE
Printed 3/30/ 79 2
3 SIGINAL(2) UNIX Programmner's Mlanual SIGNAL(2)
Access control (i.e# P'rotectionViolation)
Sexcept length violation SIGBUSTranslation not validy and
Length access control SIGSEGVReserved instruction SIGILLCustonser-reserved irestr, SISEMTReserved op'erand SIGILLReserved addressins SIGILLTrace Pending SIGTRAPV Bt instruction SIGTRAPComn~atibil1ity,-mode SIGEMTI.Chrnle SIGSEGVChills SIG3SEG'Chfifu SI GE'US
I:''
-~ Printed 3/30/79
1 .melW M
APPENDIX D - Instructions for Runins the Emulator
The emulator coder in both source and executable fornis,:s in the directory '/b/xtree/neil/kersim', The instruc-I tions in this appendix assume that this is the current work-
i inE! di rectorv.
- 1. Rurniar, the Emulatox
The terminal- operat4or must start the emulator bv enter-
4 in:s the command
,tree
The svstem will start up the kernel in each node (UNIX Pro-ces's) and prompt when its ready for commands:
command:
To start the execution of the first user Process, twof cc, rands must be entered from the terminal'
S_- To create a Process to run the code? enter
r reate niode P rio pgmwhere node node nbr or; which to create the Process
prao = the new process's priority
F-., = the user code nbr of the desired Program
The system will prin' Process name to be used in thestart command.
2. To start the execution of the process, enter
start ris-trwhere n he = the 2-part Process-name displayed when
the Process was creat d
For example- the simple Program currently in the emula-top (section5.i) can be started by executing user cooa O,-on-no-de S with prioritv 5S*
commnd:create 3 5 0Process created on node 3? named 3 1 * -
command:start 3 1
Coding aid Linkio Youz Own Usem 2mogzara
IUser Programs are written in C and are run as subrou- -
tines of a kernel Process (see section 3.3). User Programs-
March 30, 1979
H .- are restricted irn the following was-s.
- . No inp-ut operations are allowed. Any data needed m~I-vbe received Q$messages.
2 A ll variables and data must be local. Ho externals areallowed.
. P rintini statements mas be included, but should ht6I framed by the macr~os
EiABLE
-ito Preven_-t a Process switch when the stack is t po 'Large4 for the data stack save areas (section 4.2)
4. Eah *e rgrr zcie n ruet h
argmn as eue s'ie P'agmn1 oalker
The kernel call=_ oiscuasseo in section 3. may be used.
The i irs- I so;n ofeC ne user prgra taes thued i tn~ a-udl
2.T des noe :sl intiliation cuboie (fiasl'sbnah-.t'i -
rout n : ijur?: t-oasssn te sttdsraml- Inked~ t-Tht6_tabemla of routie oesaras exeutd[.) WThe--i hinr t ator which ase prora na is rssiged to the auser c6deUnumer' (seI~ hr m-dmn fth cet c6mrad=--
PEut the X o tnd 'me'. Thifras illto l the S
Updaesr I o,; il--ti- used cinkj e a(file- 'sp>1-*_-_
ah;c- aS~-~__ ae- ss~ndi h srC
a tnumb-e J
1 March :%Of , 79I- - - -- ~ W
APPZ -flTX E. Material on Future Work
Jr1 the A-l X-t rem system wit~h pagingy ho-w isa u-serprocss -"-te "-tree to- Ibe represented and man'Pulated? i
e sse n CsP a process a:s rep-resented by two blocksy tne ProcessLonro Mck ?O)end the P-ocess Work Object (P"fl1
Trhe- PC-B i-s relativei-s small and is maintained -in -the-o --, o ndei wn cn tne process as urnin.
It conai n s t he informeztior, needed by the kernel to controlthe ~-otess an ati ar. - Progrea Counter 1PC-) Mid-
Date- SItack Pc:itrB~-- arekep
The P JQ ~-g. ;.Cz in~ + loha Memory (or the beckins t4,oei c= -- #er tocl jJ -t a is Paced intO he
nC - as reoWua.j ;M Utrnisalo he workinS dats torsse for P" =2 es- ano ascon'solidajted into a sinigle-1 eLtJw- cAfn be v -e as h- : w at. Telwaddres Part t'h t UGAi fi0x ed an s~ze and hol-ds the Pro- ---cess at Lu 2; Is no needed intfhe rLD-. For eXaamolev -the- - -
rsi&t co~l-ts for th3e rrCes -Ao be- kept -ere -
p rce. -=~ rfl. t. ~--~ofpat in an nPPe nd-- -n Th i a c i qs Led In t-e conve-ti;onal &Anner for
d a fo b, lck ernz"- -rid exit.
ru(on disg, -)
- - - - - - - - - - - - -----> top -of sz7iC& -
------------ a
Noeepeily htthr sins-.trs of a_o A wh ch bel .- gs totheti"04--mss h a t- w re s~d-tv
Maetc. 30- 7
for this.
1. All X--tree code is Pure code and is not modifi ble. -96there is no need for a separate copv for each user.
24 Linkin of object modules will be done dvnamicall vatrun tirie as code modules are called.
As s result, all code is located arid Paled in to the noderdfnamicallyi as needed and there is no reauirement to haveseparate user copies of ariv code.
Concomit.ant with the lack of a separate 'code imaEe'fo.- a process is -the fact that the FC and DSP are not Justsimp:e local addresses, but are full llobal addresses con-Plete with t.iobal object names and offsets, As a result,the PC identifies the object which contains the current codefor the process. Similarlv, the DSP serves the dual func-t ion of stack Pointer and Pointer to the PWO (this ie theDSP with the offset masked tb zero).
Since the PFWO for a priocess never chanres, the 'objectnme' r'ortion of the DSP is constant for the life of theProcess. The PC, on the other handy ma% change with somefreuencw as code in new objects is invoked. In this- caseithe old PC (includins- object name) must be stored in the-- ~date stack t.o be restored -Pon return# ...
...n...tual theny the Pae table in the node mav beviewed as s table of translations from llobal addresses-to-
I ~ local addresses.
OBJECT NAME OFFSET tL.CAL "-I . . . . . . . . . . . . . . . . . . . . . . . F'I ,
Node I Id : Fa e I ,- P- -- e----------- - --- --- - - - -- -
Of course, this table is im.lemented u-n s-Ian- -- O crdeto reduce the search time. A, itionall- a tran-lat-i6h-look-aside buffer is used to eliminate the search for- mO6t,accesses in a cache-like manrner,
If the node numbers in the svstem were -fixed len.qthi-then this would suffice. However? the node numbers- in-h:-- h--
Xfinal X-tree mav be unbounded in length so a dif-erht --
scheme is necessare and is oulined below. -
IN In this new schemet all the active object names for -amrpoess are centralizEd oto one Place (currentl-d called- t h e
~C-list fo.r lavk. of a better n~ame)# This could be inc-lu dgd, ' "
Me rch 301, 197 -- '9<
. ~~~~~~~---------------- ----------- .--- ---- r?. .. E_ .. ZL=_71 ..... .-
B s ra-'t of' the PWO or as an extension to the FPCB* The vcri-6ir! ler~th node num~bers could then be nmana!§ed as a heap
Ze(either one Per process or as a central heap for each node,The ke . here is thaet each object mraw now be be referred t
b~a f4 epd lencii index into the C-list and the Process canb e unirpasela identified bv it's index int;o the table of PC-B4-takeni to.,ether tht FP and C-list indices are a fixed lengthfield which urnieuelv identifies arn object. The TL~ therfelo-okS like!
1Local FPa~e*
-------- -------- --.--------------------
0 f c ot u C-liesft." e d P Pie eere isntfudi *'V3
TLh te oftar mst firr follow the chain-: outlined-aboe t deerain--,theobjctreL4uestedr then look tip the-
loc91r- cI ni-ibe inth sme aneras before. The l OcfaI
-05
IMF;
'M arP6h 30, 1979
-4-
J~ ~ 2. ODL Clack/rjeaa~ Drie
CLOCKDIiVER do'-ice irodule:* handles clock. initerrup'tsand defines -the mnean~s for delaviris a user Processfo-.r a s~'ecif'ic length of time,
device miodule CLOCKDRIYER ECLOCK-PRIORITY];derirne deiaw;use NB""'ROCS0 awaiken
F'cbptry Pcbtwpe, Pcb;Corist WOSIZE =NBRPROCS+1;
Defines a eueue of P'rocesses (managed irr-a-circular fashion~) sorted into the order inwhich thev are to be activated4 Each entrVLicontains F. FCB Pointer arid the Proper timre- to-delaye it after the Previous Process has beenactivated,
var ~-arrv O:WQOIZE-1 of record
! :integer; -len~sth of Queuel
lMzrch 30, 1979
9 FrocediJre delays (rroc:*rcbptr*-' t.g
be si iif ' ri> then-
wh ile (->b I arid (t+oEPJ.dt<i) doic(ta[PJ~dt);
whil e r-(:-p doac'r-J .- m~IL rod WQSIZE]; 3
end'
Pcblproc-J.Psw -= cbC'Proc3,-sw or [1-33idectG('+1) mo~d WOIZIE].dty aCpj.dt);b := (b+1) mrod WQOIZE;inc je~t) A
elseawaker. (P oc;,-
eir-
whe 1 1=~ ~'ce~ cJcck.cCLci~iNTRRLJT--DDRCSJvar~~~~~dc cs '3OKSTSRGiTRAtRSJ ai
IIwhenl GCLI e;:: iIt awsken (alf'Itpcb);f :*= (f+1) mod i4QSIZE;dlee fet);
errd
b es I
040;
clock.;-end CLOCKIPRIVER
Mla rs 30P 1979