Blackfin Array HandlingPart 2

Moving an array between locations

int * MoveASM( int foo[ ], int fee[ ] , int N);

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To be tackled – Array handlingMove arrays – Max array (Exercise)

Recap

Setting up the tests Writing “enough” assembly code so you can “call the

code, and return without crashing” Move one value between arrays Moving through an array

– Hard coding and auto-increment addressing modes– Software loops– Hardware loops will be covered in a later lecture

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Build the project (F7)

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Add new tests

BUT WHY THE ERROR MESSAGE

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“Just enough code” to safely return after call to assembly code

.section program .global start_address label with : end_address label with :

HOWEVER LINKER SAYS“CAN”T FIND THIS FUNCTION”

RECOGNIZE THIS ERRORSO YOU KNOW HOW TO FIX IN THE ASSIGNMENTS AND LABS

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Use C++ keywords ‘extern “C” ‘ so compiler knows ASM follows C calling convention and not C++ calling convention

Expected test failures

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Same memory addressing error as before

INCREMENT IN 4’s with accessing int arrays

TYPOSinpar1 twice

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FIXED TYPO

R2 is INPAR 3

#define N_inpar3_R2 R2

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How do we pass back a parameter from “ASM” to “C++”

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Parameter passing convention

Pass first parameter “into” function using R0(same for data or addresses)

Pass second parameter using R1 Pass third parameter using R2 Pass 4th parameter on “stack” (like MIPS)

Return the “result of a function” using R0 as the return register

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The starting address of “final[ ]” is still (unchanged) in R2 – copy it to “return_register”

NOTE

R2 typos to be fixed

N_inpar3_R2 R2

#define N_inpar3_R2 R2

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Tests now all pass

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This code format using “index” addition can’t be looped

Stop using [P0 + 4][P0 + 8] etc

Go to auto increment mode

[P0++];

#define N_inpar3_R2 R2

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Add new tests for numpoints = 10

TEST FAILSAT THIS TIME

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Your exercise – convert to software loop format

Stop using [P0 + 4][P0 + 8] etc

Go to auto increment mode

[P0++];

#define N_inpar3_R2 R2

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Problem to solve

R0 – used for source in-parameter R1 – used for final in-parameter R2 – used for “N points” in-paramater R3 – used for “temp” when reading and writing

memory YOU CAN’T USE R4, R5, R6, R7 without saving

them to the stack. Do we have to learn about the correct way of

saving things to the stack or is there another way

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Let’s rewrite the code

R0 is used to pass in the address of the beginning of the “start” array

R0 is transferred to P0 so we can access memory

The value in R0 is not needed again in this function

Rather than learning to save things to the stack – lets re-use R0

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Value in R0not neededREUSE R0

Value in R0not neededREUSE R0

#define N_inpar3_R2 R2

N_inpar3_R2

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Exercise 1

Stop using [P0 + 4][P0 + 8] etc

Go to auto increment mode

[P0++];

#define N_inpar3_R2 R2

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Exercise 2 – Write the assembly code to determine the location of the maximum of an array

Some example tests

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Problems to solve

R0 used to pass in array address P0 R0 – therefore R0 is dead can be reused R0 reused to store temporary value when reading from memory R1 used in pass in number of points R2 used to store loop counter value R3 used to store maximum value R? used to store maximum location If use R4, R5, R6 and R7 then must learn to use “the stack” Solution 1 – use R2 as loop counter and decrement to 0 Solution 2 – store maximum location in another register

(P1) and then transfer to R0 before we leave the routine Solution 3 – use hardware loop

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Hints

Write the tests for the code running in “C” ArrayMaxLocationCPP( )

Write the code first in “C++”ArrayMaxLocationCPP( )

Use the C++ code as comments in the assembly code

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Always do a code review to make sure “code” does what you expect

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Showing only the tests that failActivateTestsmain.cpp

Change 1 line to showonly the tests that fail

| SHOW_SUCCESS;

To

; // | SHOW_SUCCESSES

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To be tackled – Array handlingMove arrays – Max array (Exercise)

Recap

Setting up the tests Writing “enough” assembly code so you can “call the

code, and return without crashing” Move one value between arrays Moving through an array

– Hard coding and auto-increment addressing modes– Software loops– Hardware loops will be covered in a later lecture