Generating “Rectify( )” Test driven development approach to TigerSHARC assembly code production Assembly code examples Part 1 of 3

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 2 / 38 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”

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 3 / 38 Software “AM” radio concept Antenna Pickup Local Oscillator Mixer Low pass Filter Rectifier Audio out RF STAGE IF STAGE AUDIO STAGE Most stages handled with high speed software Low pass Filter + amplifier

4 / 31 Standard development method Waterfall method Heavy on documentation, light on testing TLD -- IDAA Test Last Development (if done at all)

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 5 / 38 Test Driven Development CUSTOMER DEVELOPER Work with customer to check that the tests properly express what the customer wants done. Iterative process with customer “heavily involved” – “Agile” methodology.

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 6 / 38 EmbeddedUnit 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) #include

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 7 / 38 Now expand the Customer Tests to do what the customer has requested 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 8 / 38 Name mangled names needed in your assembly code can be seen from linker error messages 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 9 / 38 Next step: Write just enough code to satisfy the linker – C++ stubs

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 10 / 38 Write the assembly language stub ERROR REPORTED BY VDSP 4.0 We lost control of the processors in the debug environment.

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 11 / 38 Build the code incrementally to satisfy tests See speed change now we Are executing code – but why failures Note: -- what if N < = 0

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 12 / 38 Note Special marker Compiler optimization – speed changes FLOATS 927  THREE FOLD INTS 960  150 – SIX FOLD Why the difference in float and int? Can we do better by “writing in assembly code? code” Meaning, what is “best possible speed”? Note the failures – what are they

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 13 / 38 Fix Tests to only show “FAILURES

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 14 / 38 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 15 / 38 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 (Is it same for ints and floats?) 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( )

TigerSHARC assembly code file HalfWaveRectifyASM.asm Discuss in detail in a couple of slides 11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 16 / 38

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 17 / 38 Write tests about passing values back from an assembly code routine

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 18 / 38 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);

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 19 / 38 More detailed look at the code 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 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 20 / 38 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 21 / 38 Return registers There are many, depending on what you need to return Here we need to use J8 to return an “integer pointer value” Very slow for integer operations – good for integer pointer ops 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 J8 // J8 is a VOLATILE, NON-PRESERVED register

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 22 / 38 Using J8 for returned int * value Now passing this test “by accident Should be conditionally passing back NULL

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 23 / 38 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?

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 24 / 38 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 25 / 38 Coding convention // int *HalfWaveRectifyRelease(int initial_array[ ], // int final_array[ ], int N) #define initial_pt_inpar1 J4 incoming parameter -- pointer #define final_pt_inpar2 J5 incoming parameter -- pointer #define N_J6_inpar3 J6 incoming parameter -- integer #define return_pt_J8 J8 return value -- pointer

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 26 / 38 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 27 / 38 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 (Is it same for ints and floats?) 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( )

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 28 / 38 Doing an IF (N < 1) JUMP type of instruction 68K version CMP.L #1, D1 ; Performs subtraction (D1 – 1) and sets ; condition code flag BLT ELSE ; Branch if result of (D1 – 1) < 0 ; 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?

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 29 / 38 ELSE is a TigerSHARC keyword Should have guessed as editor turned in blue ELSE is a KEYWORD Fix that error first

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 30 / 38 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 31 / 38 Fix ELSE keyword error GREATER a keyword? Not blue Just change it to something else rather than wasting time worrying if it’s causing the problem. CHANGE IT RATHER THAN WORRY ABOUT IT

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 32 / 38 Label name is not the problem NOTE: This is “C-like” syntax, But it is not “C” Statement must end in ;; Not ;

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 33 / 38 Should learn to read – looking at wrong error. Click on error line Missing ;;

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 34 / 38 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 35 / 38 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 36 / 38 Well I thought I understood it !!! Speed issue – JUMPS can’t be too close together. Not normally a problem when “if” code is larger

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 37 / 38 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 38 / 38 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 (Is it same for ints and floats?) 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( )

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 39 / 38 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

11/2/2015 TigerSHARC assemble code 1, M. Smith, ECE, University of Calgary, Canada 40 / 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