1. Generating “Rectify( )”
Assembly code examples Part 1 of 3

2. Concepts Concepts of C++ “stubs”
Forcing the test to fail – test of test
Generating valid “C++ code” to satisfy the tests
Need for “name mangling” for overloaded functions
How do you find out the name mangled name so it can be used in assembly code
Learning just enough TigerSHARC assembly code to make things “work”
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

3. Software “AM” radio concept
RF STAGE
Antenna
Pickup
AUDIO STAGE
Low pass Filter + amplifier
Low pass Filter
Rectifier
Mixer
Local Oscillator
IF STAGE
Audio out
Most stages handled with high speed software
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

4. Test Driven Development
Work with customer to check that the tests properly express what the customer wants done. Iterative process with customer “heavily involved” – “Agile” methodology.
CUSTOMER
DEVELOPER
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

5. E-TDD Test. cpp files have four main components
E-TDD Test.cpp files have four main components. Many error messages if not present
Include Files – cut-and-paste (always the same)
TEST_CONNECT (TestFileInfo)
TEST(testNAME, testTYPE)
NOTE: Tests execute from LAST in file to FIRST. As normally the LAST test is the most recently added test, this is good.
You test if new code works and then check (regression test) that you did not break anything
LINK_TEST(TestFileInfo, testTYPE)
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

6. Now expand the Customer Tests to do what the customer has requested
Problems to be fixed in Assignment 1
Add test for
If N <= 0, return NULL otherwise return the start of the output array
Tests are working by mistake as
We are not resetting the output array
to 0 between function calls
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

7. Name mangled names can be seen from linker
C++ name as used The name mangled name generated by
in C++ code by the C++ compiler in response to function
overloading. These are the “assembly code”
names
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

8. Next step: Write just enough code to satisfy the linker – C++ stubs
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

9. Write the assembly language stub
We lost control of the processors in the debug environment.
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

10. Build the code incrementally to satisfy tests
See speed change now we
Are executing code – but why failures
Note what if N < = 0
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

11. Compiler optimization FLOATS 927  304 -- THREE FOLD
Note
Special marker
Compiler optimization
FLOATS 927  THREE FOLD
INTS 960  150 – SIX FOLD
Why the difference, and can we do better, and do we want to?
Note the failures – what are they
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

12. Fix Tests to only show “FAILURES
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

13. Generate assembly code
Do the code in steps, attempting to satisfy one test at a time
Learn “the assembler” in steps
Get “some idea” of the issues we need to learn about as we go along
Just enough knowledge “to get things to work”
Worry about full details later
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

14. What we need to know based on experiences from other processors
Can we return from an assembly language routine without crashing the processor?
Return a parameter from assembly language routine
(Is it same for ints and floats?)
Pass parameters into assembly language
Do IF THEN ELSE statements
Read and write values to memory
Read and write values in a loop
Do some mathematics on the values fetched from memory
All this stuff is demonstrated by coding HalfWaveRectifyASM( )
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

15. Write tests about passing values back from an assembly code routine
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

16. What we have learned We passed the “very general” test
Managed to call and return from an assembly code and did not crash the system
We passed some specific tests in the test file “by accident”
CJMP – is the “way to return” from an assembly code function to “C++”
Instruction format is interesting
nop; nop; nop;; ; separate instructions executed together
CJMP (ABS);; ;; indicates the end of an “grouped” instruction
CJMP must be like RTS – meaning there is a CJMP register (or memory location) storing the address to return to after this
COMPARE TO Blackfin P0 = [FP + 4]; Place storing return address
UNLINK;
JUMP (P0);
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

17. More detailed look at the code
As with 68K and Blackfin needs a .section
But name and format different
As with 68K need .align statement
Is the “4” in bytes (8 bits) or words (32 bits)
As with 68K need .global to tell other code that this function
exists
Single semi-colons
Double semi-colons
Start function label
End function label
Used for
“profiling code”
Label format similar to 68K
Needs leading underscore and final colon
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

18. Need to know How do we return “an integer pointer”
Need to look at “C++” manual for coding conventions
As with 68K, MIPS and Blackfin expect to have
Volatile registers – function variate registers, that DON’T need to be conserved when developing a function
Non-volatile, preserved registers – function invariate registers, that DO need to be conserved when developing a function
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

19. Return registers There are many, depending on what you need to return
Here we need to use J8
Many registers available – need ability to control usage
J0 to J31 – registers (integers and pointers) (SISD mode)
XR0 to XR31 – registers (integers) (SISD mode)
XFR0 to XFR31 – registers (floats) (SISD mode)
Did I also mention
I0 to I31 – registers (integers and pointers) (SISD mode)
YR0 to YR31 , YFR0 to YFR31 (SIMD mode)
XYR, YXR and R registers (SIMD mode)
And also the MIMD modes
And the double registers and the quad registers …….
#define return_pt_J8 J // J8 is a VOLATILE, NON-PRESERVED register
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

20. Using J8 for returned int * value
Now passing this test “by accident Should be conditionally passing back NULL
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

21. Conditional tests
Need to code – returning a NULL or the starting address of the final array
int *HalfWaveRectifyRelease(int initial_array[ ], int final_array[ ], int N)
if ( N < 1) return_pt = NULL;
else /* after some calculations */
return_pt = &final[ 0];
Questions to ask the instruction manual
How are parameters passed to us?
On the stack (as with 68K) or in registers / stack (as with MIPS and Blackfin)? – answer turns out to be more like MIPS and Blackfin
How do you do an IF?
How do you do conditional jumps?
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

22. Parameter passing
Spaces for first four parameters ARE ALWAYS present on the stack (as with 68K)
But the first four parameters are passed in registers (J4, J5, J6 and J7 most of the time) (as with MIPS)
The parameters passed in registers are often then stored into the spaces on the stack (like the MIPS) for “safe keeping” when assembly code functions call assembly code functions
J4, J5, J6 and J7 are volatile, non-preserved registers
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

23. Coding convention // int *HalfWaveRectifyRelease(int initial_array[ ],
// int final_array[ ], int N)
#define initial_pt_inpar1 J4 incoming parameters
#define final_pt_inpar2 J5
#define N_J6_inpar J6
#define return_pt_J J8 return value
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

24. Can we pass back the start of the final array
Still passing tests by accident and the start of the array needs to be conditional return value
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

25. What we need to know based on experiences from other processors
Can we return from an assembly language routine without crashing the processor?
Return a parameter from assembly language routine
(Is it same for ints and floats?)
Pass parameters into assembly language
Do IF THEN ELSE statements
Read and write values to memory
Read and write values in a loop
Do some mathematics on the values fetched from memory
All this stuff is demonstrated by coding HalfWaveRectifyASM( )
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

26. Doing an IF (N < 1) JUMP type of instruction
68K version
CMP.L #1, D ; Performs subtraction (D1 – 1) and sets ; condition code flag
BLT ELSE ; Branch if result of (D1 – 1) < ; BLE is a branch if less than ; zero instruction NOT on whether D1 < 1
TigerSHARC version
COMP(N_inpar3, 1);; // Perform N < 1 test
IF JLT, JUMP ELSE;; // NOTE: Use of comma , and semi-colons ;;
Same possible error on BOTH processors
68K which test BLE, BLT or BGT should be used?
TigerSHARC – which test JLE, JLT or NJLE should be used?
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

27. ELSE is a TigerSHARC keyword Should have guessed as editor turned in blue
ELSE is a KEYWORD
Fix that error first
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

28. Why is ELSE a keyword FOUR PART ELSE INSTRUCTION IS LEGAL
IF JLT; ELSE, J1 = J2 + J3; // Conditional execution – if true ELSE, XR1 = XR2 + XR3; // Conditional – if true YFR1 = YFR2 + YFR3;; // Unconditional -- always
IF JLT; DO, J1 = J2 + J3; // Conditional execution -- if true DO, XR1 = XR2 + XR3; // Conditional -- if true YFR1 = YFR2 + YFR3;; // Unconditional -- always
Having this sort of format means that the instruction pipeline is not disrupted by jumps when we do IF statements
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

29. Fix ELSE keyword error GREATER a keyword? Not blue
Just change it to something else rather than wasting time
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

30. Label name is not the problem
NOTE:
This is “C-like” syntax,
But it is not “C”
Statement must end in ;;
Not ;
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

31. Should learn to read – looking at wrong error. Click on error line
Missing ;;
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

32. Still not got the correct syntax
Because of missing ;; (dual semicolons)
Processor thinks we want
return_pt = 0; JUMP END_IF; return_pt = INPAR3 ;;
Apparently such a complicated instruction IS LEGAL provided the jump is at the start of the multiple issue instruction
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

33. Add dual-semicolons everywhere Worry about “multiple issues” later
This dual semi-colon
Is so important that you
MUST code review for it all
the time or else you waste
so much time in the
Lab. Key in exams / quizzes
At last an error I know how to fix 
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

34. Well I thought I understood it !!!
Speed issue – JUMPS can’t be too close together.
Not normally a problem when “if” is larger
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

35. Add a single instruction of 4 NOPs nop; nop; nop; nop;;
Fix the last error as part of Assignment 1
Fix the remaining error
in handling the IF THEN ELSE
as part of assignment 1
Worry about code efficiency later
(refactor) when all code working
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

36. What we need to know based on experiences from other processors
Can we return from an assembly language routine without crashing the processor?
Return a parameter from assembly language routine
(Is it same for ints and floats?)
Pass parameters into assembly language
Do IF THEN ELSE statements
Read and write values to memory
Read and write values in a loop
Do some mathematics on the values fetched from memory
All this stuff is demonstrated by coding HalfWaveRectifyASM( )
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

37. Assignment 1 – code the following as a software loop – follow 68K approach
extern “C” int CalculateSum(void) {
int sum = 0;
for (int count = 0; count < 6; count++) {
sum = sum + count; }
return sum;
extern “C” – means that this function is “C” compatible rather than “C++”.
No overloading (requiring name-mangling) permitted
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada

38. Reminder – software for-loop becomes “while loop” with initial test
extern “C” int CalculateSum(void) {
int sum = 0;
int count = 0;
while (count < 6) {
sum = sum + count;
count++; }
return sum;
Do line by line translation
11/15/2018
TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada