cse 466 – fall 2000 - introduction - 1 reentrant driver open() { if (count++) return(0); else...

$: CSE 466 – Fall 2000 - Introduction - 1 Reentrant Driver open() { if (count++) return(0); else return(grab_resources()); } release() { if (--count) return(0);$
CSE 466 – Fall 2000 - Introduction - 1

Reentrant Driver

open() {

if (count++) return(0);

else return(grab_resources());

}

release() {

if (--count) return(0);

else return(release_resources());

}

read() {

if (read_count++) sleep_on_interruptible(&wq);

else {

start = getTime();

INIT = 1;

sleep_on_interruptible(wq);

INIT = 0;

}

compute_distance();

copy_to_user();

if (--read_count) INIT == ;

return(length);

}

isr() {

stop = getTime();

wake_on_interruptible(wq);

}

read() {if (INIT) sleep_on(&wq);else {

start = getTime();INIT = 1;sleep_on(wq);

}compute_distance();copy_to_user();return;

}isr() {

stop = getTime();INIT = 0; compute_distance()wake_on(wq);

}

still: a new readthat occurs before the queue is emptied will overwrite “start”wakeINIT=0readblocked reader computes wrong distance

problem:processes added to wqafter wake_on may never get awakened!They have to wait untila read is attempted afterthe queue is emptied and INITis turned off.read after wake problem


Use a Bottom Half!read() {

if (INIT) sleep_on(wq);

else {

start = getTime();

INIT = 1;

sleep_on(wq);

}

copy_to_user();

if (empty(wq)) INIT = 0;

return;

}

isr() { // reads will still pile up on the wait queue until the bh executes.

stop = getTime();

add_to_bh_queue(isr_bh);

}

isr_bh() { // make a new queue for all future reads, compute distance with correct start-stop data.

sonar_result = Compute_distance(); // do this once per interrupt

INIT = 0;

tmp = wq; // re-initialize queue to catch for read calls

wq = (wait_queue*) kmalloc(sizeof(wait_queue));

wake_on(tmp); // wake old queue

}

will each reader get the “correct” reading?


FIFO’s, which are named pipes

Process 1void main() { mknod(“/tmp/myfifo”, S_IFIFO ); // create a FIFO file node

f = open(“/tmp/myfifo”, O_WRONLY);while (1) {generate_data(buf); write(q, buf, n);}

}

Process 2void main() {

f = open(“/tmp/myfifo”, O_RDONLY);while (1) {read(q, buf, n); process_data(buf);}

}

Works for “unrelated” processes

Multiple writers, Multiple readers Kernel ensures mutual exclusion Kernel does not control interleaving of writers, readers


Multi-Processor Systems A Control Dominated Example

H2

Air

H20

Heat

controllersense:

•Temperature•H2

•Output Current•Output Voltage•Fan Speed

control•H2 valves•Output MOSFET•Fan Speed•Stack MOSFETS

not showing power supply circuitry for the controller…runs off fuel cell w/ backup battery.


System level Modes (Logical Structure)

startup warmup online

offlineshtdwnSelf Check

Fail

WarmOn

Overload+Off

Self CheckPass Error

Error

Error

Error

off


State Table (*error conditions are mode dependent)

Mode Outputs Tasks Signals

New Mode

Off Load Disabled Power Supply OffGas Valves ClosedPower Button Enabled

none Power Button Push Startup

Startup Load DisabledPower Supply OnGas Valves ClosedInitialize

Temp ControlH2 DetectionLoad MonitorUI Running

Initialize Complete

Warm Up

Error Condition Detected* or shutdown request

Shutdown

Warmup Load DisabledPower Supply OnGas Valves Open

Temp Control H2 DetectionLoad MonitorUI Running

Operating Temp Reached Off Line

Error Condition Detected* or shutdown request

Shutdown

Off Line Load DisabledPower Supply OnGas Valves Open


On-Line Command Received (UI)

On Line

Error Condition or Shutdown request

Shutdown

On Line Load EnabledPower Supply OnGas Valves Open


Off Line Command Off Line

Overload Off Line

Error Condition* or Shutdown Request

Shutdown

Shutdown Load DisabledPower Supply OnGas Valves ClosedFan On

Temp ControlSchedule transition to Off state

Timeout Off


Examples of Mode Dependencies

Fan Speed Control: In startup or shutdown mode always run minimum speed otherwise attempt to maintain temperature set point If fan doesn’t turn, issue badfan signal

Hydrogen Detection: always close hydrogen valves and issue h2dectected signal if hydrogen detected, except in startup mode.

Load Monitoring If not online and output current > 0 or output voltage < min, then issue

mosfet failure signal If online and load current is > max allowed, or if output voltage is < min

then turn on another stack. If all stacks are on, then issue overload signal.

UI Process If “line” button pushed and online issue offline event, If offline issue online signal.

If “power” button pushed and not in off mode, then issue shutdown signal.


Logical Decomposition

UINextStateLogic

signals

signals

Temp

Load

H2 Task

Output Logic

inputs


Logical Implementation

task stateMgr _task_ 0 {while (1) {

recv_signal(&s); // blockingswitch(state)

startUp: switch(s) TOOHOT: state = SHTDWN;…

break;…

}

synchronized volatile state;

task tempControl _task_ 1 {

while(1) {

t = readTemp();if (t > MAXT) send_signal(TOOHOT); //blockingif (t < MINT) send_signal(TOOCOLD);if (t < setpoint)

increase_fan_speed();if (t > setpoint)

decrease_fan_speed();wait(ThermalTime);

}}

task loadMonitor _task_ 2 {

while(1){

if (state != ONLINE)

if (getLoad() > 0) send_signal(BADFET);

else if (getLoad() > MAXLOAD) send_signal(OVRLOAD);

wait(LoadTime);

}}

task H2Monitor _task_ 3 {

while (1) {

if (state() != startUp)

if ((getH2() < MINH) || (getH2() > MAXH)) send_signal(H2FAILURE);

}} // let this process fill in all unused cycles!

Issues: what are send_signal() and recv_signal()?How can synchronized state be implemented?


Physical Decomposition -- Layers

StateMgr +UI

load

temp

H2

Socket could be implemented in shared memory, internet, or anything in between.

High level architecture can be independent of implementation choices.

Synthesis Problem:Map processes and sockets to processors and networks. Optimize performance,latency, shared mem.

Warning: usually not done this way for embedded systems…usually designer performs the physical decomposition andapp is written to thehardware…not a good idea!

state

signals

physical layer

network layer

applicationlayer


Example of Physical Layer: SPI Bus

Master Slave

SCK

SDO

SDI

SCK

SDI

SDO

void isr() interrupt TIMER { SDR = S; while(!SPF); R = SDR;}

void isr() interrupt SPF{ R = SDR; SDR = S signal(RECV);}

1 0 0 1 1 1 1 0

shift reg

0 0 0 1 1 0 0 0

shift reg


Multiple Slave Configuration

Master Slave

SCK

SDO

SDI

SCK

SDI

SDO

Slave

SCK

SDI

SDO


ISO Layers Continued Transport Layer: responsible for end-to-end protocol of user data buffer transmissions.

Source and destination addresses are private – host to host. Maps application space channel (socket) name to network address. makes network packets w/ transport header and communicates w/ network layer.

Each layer has a peer-to-peer and an intra-stack protocol

Transport -- TCP

Network -- IP

Datalink -- Ether

Physical -- Ether ethernet fiber

Datalink -- Ether

Network -- IP

fiber ethernet

Datalink -- Ether

Network -- IP

Transport -- TCP

Network -- IP

Datalink -- Ether

Physical -- Ether

write(s, buf,n); read(s, buf,n );

Application Application


Transport

Network -- IP Network -- IP

Transport

Network -- IP Network -- IP

Embedded Networking: Simplest Case Simple case: socket name is the same as physical address. No mapping, we just need

to break our message into frames…maybe

Physical Layer – typically low bandwidth, serial, byte oriented

Data link layer – read/write interface to the application

frames: destination address, data, checksum. No mapping from sockets to network address No mapping from network address to physical address (no routing)

Datalink

Physical ethernet fiber

Datalink -- Ether

fiber ethernet

Datalink -- Ether Datalink

Physical

write(s, buf,n); read(s, buf,n );

Application Application


Master Slave Data Link Protocol

As an example frame is [destination address, command, data]

An acknowledgement frame is [address, data, checksum]

Master Slave

SCK

SDO

SDI

SCK

SDI

SDO

Slave

SCK

SDI

SDO

mux

dst cmd data dst type data

addr data sum type data sum

mux x x x 1 1 1 2 2 2


Multi-master Systems: I2C

Multi-mastered

Send and receive

Two wire (plus ground)

Packet oriented (block send)


Major Features of I2C


Physical Layer


Bit Transfer

Transmitter

Master


Who gets to be master

The one who initiates a frame:

A frame is:<Start><addr><data>…<data><Stop> OR<Start><addr><data>…<data><R_Start><addr><data>…<Stop>


An I2C Byte Transfer

Tx Device Rx Device

master

slave slave

Rx

MSB First

MSB……………….LSB


A Complete Frame

MSB……..LSB


Beauty of Layers

App doesn’t care if lower layer is SPI or I2C

How much can we isolate the physical differences?

cse 466 – fall 2000 - introduction - 1 reentrant driver open() { if (count++) return(0); else...

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