works for other quizzes and exams too 1 hints for post-lab quiz 1

Works for other quizzes and exams too

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Hints for Post-Lab Quiz 1

Three types of questions

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Basic Knowledge Questions

Translation QuestionsYou are given the C++ and must convert into

Blackfin assembly code

Design questionsWork out what is neededGenerate the design – in C++ or in pseudo

codeMost often – convert design code into

Blackfin assembly code

Knowledge type question example

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A) Circle and label with an A -- the icon (menu item) that causes VisualDSP to compile the C++ code, but not build or rebuild the full project.

B) Circle and label with a B -- a Blackfin instruction where a non-volatile register is recovered from the stack.

CORRECTOR WRONGANSWERNO PARTIAL MARKS

Sometimes more than one correct answer

The Rosetta Stone “Question”You understand columns 1 and 2

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C++ codeC++ codeNEW C++ keywordNEW C++ keyword

extern “C” long int extern “C” long int Return1( ); Return1( );

long int Return1( ){long int Return1( ){ return 1; return 1;}}

Blackfin codeBlackfin code

.section program;.section program; .global _Return1; .global _Return1;

_Return1:_Return1: LINK 16; LINK 16;

R0 = 1;R0 = 1; UNLINK;UNLINK; RTS; RTS;

68K code68K code

.section code;.section code; .global _Return1; .global _Return1;

_Return1:_Return1: LINK #-16, A4; LINK #-16, A4;

MOVE.L #1, D0;MOVE.L #1, D0; UNLINK A4;UNLINK A4; RTS; RTS;

Demonstrates ability to transfer knowledgeWhich register is used as the 68K return register?

In this code, which register is used as the 68K frame pointer?

C++ to assembly Example

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ACCURACYIMPORTANT

TRY TO MATCH ASSEMBLY CODE TO C++ ON A BOX BY BOX BASIS

THEN EASIER TO GIVEPARTIAL MARKS

#define count_R1 R1count_R1 = 0;

Design question exampleActs like one part of the laboratory

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Design Question

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Next to impossible to mark if not well documentedTherefore many marks are given for the C++

or pseudo-code comments

More chance of partial marks if the register names are self documenting

Register documentation example

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ID_R1.L = lo(CHIPID); // Marker know thatID_R1.H = hi(CHIPID); // R1 used to store ID

CC = ID_R1 == version_INPAR_R0; // Marker knows that // R0 used for version// Marker also know that you know first parameter is passed in R0// and not on the stack – later if you make a mistake version_R1then still a good chance for partial (or full) mark

Avoid errors that would take a lot of time to fix in the laboratory

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Always check for possible return address and stack errorsLINK -- at the start of a functionUNLINK -- at the end of a function

Always check for NAME_MANGLINGVariable _fooarray;Function _FeeFunction__Fv (void) _FeeFunction__Fl (long int)

_FeeFunction__NM (not sure) _FeeFunction__NM2 (different not sure)

WITH NAME MANGLING – under exam conditions, more interested in that you understand the concept than whether you are getting it exactly correct

Avoid pointer errors that would take a lot of time to fix in the laboratory

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If the memory location is shown as extern in C++ or .extern in Assembly

extern long int funVariable;

.extern _funVariable;

.section program // will accept .section code

P0.L = lo(_funVariable);P0.H = hi(_funVariable);

_funInRegisterR0 = [P0];


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If the memory location is shown without the word EXTERN long int funVariable = 0;

.section L1_data1; // will accept data, data1 .global _funVariable; .var _funVariable = 0; // Follow the C++ code

funVariable is IN MEMORY and not yet in a register You must move the value from memory into a register

.section program P0.L = lo(_funVariable); IS P0.L = _funVariable P0.H = hi( _funVariable); OKAY?

funInRegisterR0 = [P0];


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If the memory location is known to be part of the special MEMORY LOCATIONS (MMR) used to control special operations of the Blackfin “peripherals”

#include <defBF533.h> // will accept <defs.h>#include <macros.h> // will accept <macro.h>

.section program P0.L = lo(TCOUNT); // will accept HI( ) and LO ( )

P0.H = hi(TCOUNT);countInRegisterR0 = [P0];

Know what the hi( ) and lo( ) macros do

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.section program P0.L = lo(TCOUNT);

P0.H = hi(TCOUNT);

MEANS

P0.L = TCOUNT & 0xFFFF; P0.H = (TCOUNT & 0xFFFF0000) >>16

HINT – #define CONSTANTSdon’t use CONSTANTS

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#define MAXVALUE 44000 Either hex or decimal is okay

.section program R0.L = lo(MAXVALUE);

R0.H = hi(MAXVALUE);

HINT: If the person is following “standard” coding conventions then CAPITIALS MEAN CONSTANT – use hi(), lo( )

HINT – Will work for small constants too

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#define MAXVALUE 22000 Either hex or decimal is okay

.section program R0.L = lo(MAXVALUE);

R0.H = hi(MAXVALUE);

BUT IN THIS CASE – since the constant is small (short int size) R0 = MAXVALUE;

Or R0 = 6;

HINT: If it looks like IT MIGHT BE a big constant, then let the assembler worry about it -- use hi( ) and lo( )

Condition codes

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99999 times out of 100000 the following is wrong

CC = R0 < number; e.g. CC = R0 < 25;

So play the odds

R1 = number; CC = R0 < R1;

Will accept CC = (R0 < R1); under exam conditionsWILL NOT ACCEPT CC = R1 > R0;

CC conditions are always checked VERY closely as they cause so much problem in the laboratory and in “real life”

LOAD AND STORE OPERATIONS

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Rule to remember – if the operation would not work on the MIPS, then it will not work on the Blackfin or any other RISC processor

register memory R0 = [P1];memory register [P1] = R0;

NEVER add to memory, [P1] = [P0] +1; add to register R0 = R0 + [P0];

Register operationsAdd a small number

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Make sure that you get the common instructions correct – there are not many

R0 += pretty_small_number R0 += 6 or R0 += -10;

NOT R0 = R0 + 6;

Pretty_small_numbers are just that – pretty small numbers -64 <= num <= +63

Register operationsAdd a larger number

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Make sure that you get the common instructions correct – there are not many instructions that you need to be concerned with

R1 = larger_number;R0 = R0 + R1;

R1 = 0x2000; R0 = R0 + R1; NOT R0 += R1;

R1 = 20000; R0 = R0 + R1;

R1.L = lo(40000); R1.H = hi(40000); R0 = R0 + R1;

HINT: Hexadecimal numbers are easy to work out if they are small (need 16-bits) or very large (need 32-bits). Decimal numbers are not – PLAY THE ODDS – if it looks large in decimal – then use lo( ), hi( ) approach

Other instructions we have used

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Make sure that you get the common instructions correct – there are not many common instructions to worry about

JUMP LABEL_END; // OFTEN JUMP (P0); // typically end of function


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CALL _FeePassVoidFunction__Fv

// void FeePassVoidFunction(void);

NOTE: CALL _FeePassVoidFunction__Fv

// long int FeePassVoidFunction(void); // Returns a value in R0;


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// void FeePassLongIntFunction(long int); CALL _FeePassLongIntFunction__Fl (little L)

CALL _FeePassLongIntFunction__NM -- okay in exam

CALL _FeePassIntFunction__Fi (little I) // void FeePassIntFunction(long int);

CALL _FeePassIntFunction__NM2 -- okay in exam


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R0 = 7; CALL _FeeFunction__Fl; // FeeFunction( 7);

R1 = 6; R0 = 7; CALL _FumFunction__NM; // FumFunction(7, 6 );


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R0 = 7; CALL _FeeFunction__Fl; // FeeFunction( 7);

R1 = 6; R0 = 7; CALL _FumFunction__NM; // FumFunction(7, 6 );

When to use a register andwhen to use memory

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.extern _value; // extern long int value .section L1_data; .global _fum_value; // long int fum_value;

.var _fum_value;

.section program; .global _FooFunction__Fl; // void FooFunction(long int passed_Fickle) {_FooFunction__Fl: LINK 16;

passed_Fickle_R0 += 6; // passed_Fickle = passed_Fickle +6; P0.H = hi(_value); P0.L = lo(_value); // value = value + 6; R1 = [P0]; R1 += 6;

[P0] = R1;

P1.H = hi(_fum_value); P1.L = lo(_fum_value); // fum_value = fum_value + 6; R2 = [P1]; R2 += 6; [P1] = R2; ……… // Rest of the function

When to use a register andwhen to use memory

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.section program; .global _FooFunction__Fl; // void FooFunction(long int passed_Fickle) {

_FooFunction__Fl: LINK 16;

passed_Fickle_R0 += 6; // passed_Fickle = passed_Fickle +6;

#define value_R1 R1 // long int value value_R1 += 6; // value = value + 6;

#define fum_valueR2 R2 // long int fum_value; fum_value_R2 += 6; // fum_value = fum_value + 6;

……… // Rest of the function

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Other requested question and answers

works for other quizzes and exams too 1 hints for post-lab quiz 1

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