Works for other quizzes and exams too A FEW SLIDES ARE UPDATED OVER THE SLIDES IN THE NOTES 1 Hints for Post-Lab Quiz 1

Three types of questions 2 Basic Knowledge Questions Translation Questions You are given the C++ and must convert into Blackfin assembly code Design questions Work out what is needed Generate the design – in C++ or in pseudo code Most often – convert design code into Blackfin assembly code

Knowledge type question example 3 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. CORRECT OR WRONG ANSWER NO PARTIAL MARKS Sometimes more than one correct answer

The Rosetta Stone “Question” You understand columns 1 and 2 4 C++ code NEW C++ keyword extern “C” long int Return1( ); long int Return1( ){ return 1; } Blackfin code.section program;.global _Return1;.section program;.global _Return1; _Return1: LINK 16; R0 = 1; R0 = 1; UNLINK; RTS; UNLINK; RTS; 68K code.section code;.global _Return1;.section code;.global _Return1; _Return1: LINK #-16, A4; MOVE.L #1, D0; MOVE.L #1, D0; UNLINK A4; RTS; UNLINK A4; RTS; Demonstrates ability to transfer knowledge Which register is used as the 68K return register? In this code, which register is used as the 68K frame pointer?

Design question example Acts like one part of a “quiz laboratory” 5

First design the code in pseudo “C” #include bool ChipVersion(version) { chipID = *pCHIPID & 0xF; if (chipID == version) return true; else return false; } Same sort of code as ReadTemperature in Assign 1 6

Now forget the question and just translate the code “line by line” 7 #include bool ChipVersion(version) { chipID = *pCHIPID & 0xF; if (chipID == version) return true; else return false; } #include #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 8 ACCURACY IMPORTANT TRY TO MATCH ASSEMBLY CODE TO C++ ON A BOX BY BOX BASIS THEN EASIER TO GIVE PARTIAL MARKS #define count_R1 R1 count_R1 = 0;

Design Question 9 Next to impossible to mark if not well documented Therefore 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 10 ID_R1.L = lo(CHIPID); // Marker know that ID_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_R1 then still a good chance for partial (or full) mark

Avoid errors that would take a lot of time to fix in the laboratory. 11 Always check for possible return address and stack errors LINK -- at the start of a function UNLINK -- at the end of a function Always check for NAME_MANGLING unless 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 way that saves time in Labs. Because the same technique saves me time when marking

Avoid pointer errors that would take a lot of time to fix in the laboratory 12 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];

Avoid pointer errors that would take a lot of time to fix in the laboratory 13 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];

Avoid pointer errors that would take a lot of time to fix in the laboratory 14 If the memory location is known to be part of the special MEMORY LOCATIONS (MMR) used to control special operations of the Blackfin “peripherals” #include.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 15.section program P0.L = lo(TCOUNT); P0.H = hi(TCOUNT); MEANS P0.L = TCOUNT & 0xFFFF; P0.H = (TCOUNT & 0xFFFF0000) >>16

HINT – #define value CONSTANTS don’t use magic numbers ( CONSTANTS with no meaning) Easier to mark -- MEANS more marks 16 #define MAXVALUE 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?) 17 #define MAXVALUE 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 problems Code that would waste time in lab, loses marks in Quizzes times out of 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 19 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 operations Add a small number 20 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 operations Add a larger number 21 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 22 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])

Other instructions we have used 23 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 class CALL _FeePassVoidFunction

Other instructions we have used 24 Make sure that you get the common instructions correct – there are not many // 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

Other instructions we have used 25 Make sure that you get the common instructions correct – there are not many R0 = 7; CALL _FeeFunction__Fl; // FeeFunction( 7); R1 = 6; R0 = 7; CALL _FumFunction__NM; // FumFunction(7, 6 );

When to use a register and when to use memory 26.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 and when to use memory 27.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

28 Other requested question and answers