Blackfin Array Handling Part 2

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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
• CANT 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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TYPOSinpar1 twice
Same memory addressing error as before INCREMENT
IN 4s with accessing int arrays
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define N_inpar3_R2 R2
FIXED TYPO R2 is INPAR 3
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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
define N_inpar3_R2 R2
NOTER2 typos to be fixed N_inpar3_R2 R2
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Tests now all pass
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This code format using index addition cant be
looped
define N_inpar3_R2 R2
Stop using P0 4P0 8 etc Go to auto
increment mode P0
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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
define N_inpar3_R2 R2
Stop using P0 4P0 8 etc Go to auto
increment mode P0
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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 CANT 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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Lets 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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define N_inpar3_R2 R2
Value in R0not neededREUSE R0
N_inpar3_R2
Value in R0not neededREUSE R0
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Exercise 1
define N_inpar3_R2 R2
Stop using P0 4P0 8 etc Go to auto
increment mode P0
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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 CArrayMaxLocationCPP(
  )
• 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 fail
ActivateTestsmain.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