Introduction to Embedded Systems. Some Nagging

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1 Introduction to Embedded Systems CS/ECE 6780/5780 Al Davis Today s topics: some logistics nagging assembly language programming 1 CS 5780 Some Nagging Apparently necessary several students do not yet have lab partners or lab sections identified» lab section is your choice but you have to let me know via » note this is due TODAY registered but not on list» Min, Najar, Sreedharan, Tateoka team identified but no lab section» Bailey & McDougall, Tomer & Oneida no team or lab section» Behera, Fallatah, Jones, Lezin, Maheshwari, Martin, Min» Morley, Najar, Rolfe, Sreedharan, Tateoka, Wiser, Worley If your name appears above - see me after class note I may have some book-keeping errors» but we have to get this sorted out» lab section assignments will appear on the web today if you spot an error teach-cs5780 ASAP 2 CS 5780 Page 1

2 Why Assembly? Taken ECE/CS 4400? then you know Typically you ll write your lab codes in C if everything works» then no need for assembly/object code knowledge if it doesn t work» examine assembly to see what the compiler did to your code» and some things are just easier in assembly direct control of machine resources you can embed assembly code in your C code files works in simulator but not on the processor» processor only knows bits object code Hence you ll need to be familiar with assembly and object code representations» you ll probably do this in JIT mode 3 CS 5780 Assembly Language Development Process 4 CS 5780 Page 2

3 6812 Assembly Language Details are in references on the web page too boring to enumerate in class so we ll cover the highlights Addresses and symbols assembler usually is a 2-pass process» 1: build the symbol table:values map explicit value PTT equ $2040 implicit value: label a particular location in the code» 2: create object file based on symbol table phasing error results if symbol value differs between passes Result is a listing file errors are listed if they occur» undefined symbol, illegal opcode, branch distance too far, etc.» symbol table values» hex object code 5 CS 5780 Syntax 6 CS 5780 Page 3

Syntax Basic model First character is important white space no label * or ; comment line character,., or _ label» case sensitive composed of digits, characters,.

4 Syntax Basic model First character is important white space no label * or ; comment line character,., or _ label» case sensitive composed of digits, characters,., $, _ advice: develop a label convention and stick to it Labels (optional : which is ignored) define only once except when defined by set value is an address of next instruction unless defined by equ or set 7 CS 5780 More Syntax 8 CS 5780 Page 4

5 Operand Types 9 CS 5780 Indexed Addressing Mode 10 CS 5780 Page 5

6 Building the Object Code 11 CS 5780 Auto Pre/Post Dec/Inc Indexed Mode Why not the PC register? 12 CS 5780 Page 6

7 Building the Object Code 13 CS 5780 Accumulator Offset Indexed 14 CS 5780 Page 7

8 Indexed Indirect Mode 15 CS 5780 Accumulator D Offset Indexed Indirect 16 CS 5780 Page 8

9 Load Effective Address LEAS load effective address into SP 17 CS 5780 Load and Store Instructions Register Memory moves load instructions: ldaa, ldab, ldd, lds, ldx, ldy» modes are IMM, DIR, EXT, IND store instructions: staa, stab, std, sts, stx, sty» modes are DIR, EXT, IND CC N & Z bits updated based on moved value Examples 18 CS 5780 Page 9

10 M2M Move Instructions Move a value from one memory location to another does not affect the CC register bits 19 CS 5780 Clear/Set Instructions 20 CS 5780 Page 10

11 Exchange and Transfer Instructions Transfer (all INH) tab: A B (also tba) tap: A CC (also tpa) tsx, txs, tsy, tys, etc. see manual for full set Exchange (also INH) double move» xgdx, xgdy 21 CS 5780 Add and Subtract 22 CS 5780 Page 11

12 Compare 23 CS 5780 Misc. Arithmetic Instructions Dec/Inc, Negate, Test 24 CS 5780 Page 12

13 Multiply 25 CS 5780 Integer Divide 26 CS 5780 Page 13

14 Fractional Divide 27 CS 5780 fdiv Example 28 CS 5780 Page 14

15 Extended Precision Arithmetic 29 CS 5780 MAC 30 CS 5780 Page 15

16 Shifts 31 CS 5780 Rotate 32 CS 5780 Page 16

17 Bitwise Logical Operations 33 CS 5780 Bit Test, Set, & Clear 34 CS 5780 Page 17

18 Stack Instructions REMEMBER: stack grows down (lower address value) 35 CS 5780 Subroutine Linkage (Manual) Callee saves state to stack Restores state on return 36 CS 5780 Page 18

19 Subroutine Call and Return bsr offset is 8-bit signed value 37 CS 5780 Jump, Branch, Branch Always 38 CS 5780 Page 19

20 Single Condition Branches hard to say what this is good for 39 CS 5780 Example: Equality Tests 40 CS 5780 Page 20

21 Unsigned Number Branches 41 CS 5780 Signed Number Branches 42 CS 5780 Page 21

22 Example: Unsigned Tests 43 CS 5780 Miscellaneous But Useful 44 CS 5780 Page 22

23 Assembler Pseudo-Ops 45 CS 5780 More Pseudo-Ops 46 CS 5780 Page 23

24 Concluding Remarks Boring and still incomplete hopefully you have background to read understand the ISA & assembler» read the reference documentation for the whole scoop Addressing modes are the key to reading and writing assembly you ll tend to read it more than write debug write usually only happens when you need low-level HW control condition codes and subsequent branches are important» ignore and bugs appear Extensive math support for operations wider than 8 bits Assembly coding is hard easy to make basic and serious mistakes» save & restore state, mis-matched stack frames, CC screw-ups» Pandora s box in a way 47 CS 5780 Page 24

Table 1: Mnemonics Operations Dictionary. Add Accumulators Add B to Y. Add with carry to B. Add Memory to B. Add 16-bit to D And B with Memory

Table 1: Mnemonics Operations Dictionary. Add Accumulators Add B to Y. Add with carry to B. Add Memory to B. Add 16-bit to D And B with Memory Table 1: Mnemonics s Dictionary ABA ABX ABY ADCA ADCB ADDA ADDB ADDD ANDA ANDB ASL ASLA ASLB ASLD ASR ASRA ASRB BCC BCLR BCS BEQ BGE BGT BHI BHS BITA BITB BLE BLO BLS BLT Add Accumulators Add B to X Add