works for other quizzes and exams too a few slides are updated over the slides in the notes 1 hints...

Works for other quizzes and exams too

A FEW SLIDES AREUPDATED

OVER THE SLIDES IN THE NOTES1

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++ code

NEW 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?

Design question exampleActs like one part of a “quiz laboratory”

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First design the code in pseudo “C”

#include <blackfin.h>

bool ChipVersion(version) {

chipID = *pCHIPID & 0xF;

if (chipID == version)

return true;

else

return false;

}

Same sort of code as ReadTemperature in Assign 1

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Now forget the question and just translate the code “line by line”

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bool ChipVersion(version) {

chipID = *pCHIPID & 0xF;

if (chipID == version)

return true;

else

return false;

}

#include <blackfin.h>#define TRUE 1#define FALSE 0

.section program. .global _ChipVersion;// VERSION IS PARAMETER IN R0_ChipVersion:

P0.L = lo(CHIP_ID); P0.H(…) chipID _R2 = [ID_ADDRESS_P0]; mask_R1 = 0xF; chipID _R2 = chipID _R2 & mask_R1;

temp_return_R1 = TRUE; NOT R0

COMP(chipID _R2, inpar_R0);

IF CC JUMP DONE temp_return_R1 = FALSE;

DONE: return_R0 = temp_return_R1;

….END: RTS

Code was

return value = TRUE

If (chipID = version) then returnValue = false

Return returnValue;

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 R1

count_R1 = 0;

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_MANGLINGunless using ‘extern “C” ‘ Variable _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

We are using extern “C” to this point in the class. We will get to “function overloading” and “name_mangling” at a latter date

I give marks for you coding in a waythat saves time in Labs.

Because the same techniquesaves me time when marking

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”


.section program; // Will NOT accept missing sections

P0.L = lo(TCOUNT); // will accept HI( ) and LO ( )P0.H = hi(TCOUNT);countInRegisterR0 = [P0];

Understanding what the hi( ) and lo( ) macros do helps in understanding when to use them

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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 value CONSTANTSdon’t use magic numbers (CONSTANTS with no meaning)

Easier to mark -- MEANS more marks

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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 – Hi, Lo will work for small constants too – and saves anxiety (Do I need to do hi / low or not?)

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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 cause problemsCode that would waste time in lab, loses marks in Quizzes

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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 – Use the Blackfin (MIPS) RISC register and register operation

R1 = number; CC = R0 < R1;

Will accept CC = (R0 < R1); under exam conditions – extra brackets WILL NOT ACCEPT CC = R1 > R0;

CC conditions are always checked VERY closely in exams 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; no memory constant

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 to remember

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 after the jump address has been put into P0 (e.g. P0 = [FP + 4])


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

CALL _FeePassVoidFunction__Fv // void FeePassVoidFunction(void);

NOTE: CALL _FeePassVoidFunction__Fv // long int FeePassVoidFunction(void); // Returns a value in R0;

extern “C” _FeePassVoidFunction – used in this classCALL _FeePassVoidFunction


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

CALL _FeePassLongIntFunction__NM -- okay in exam because it means that you known that this name is NM (name mangled) and could look up the answer if the exam was open book

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 );

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

Variable “outside” a function

MUST BE STORED IN MEMORY.setion L1_DATA

Very often the answer must be got from memory. Some math done and then put back into memory

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

Variable passed into a function

Is already in a register

R0 in this case

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Other requested question and answers

works for other quizzes and exams too a few slides are updated over the slides in the notes 1 hints...

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