1. ECE 353 Introduction to Microprocessor Systems Michael G. Morrow, P.E. Week 6

2. Procedures Types Nesting Context Save/Restore Assembling/Linking Multiple Source Files Parameter Passing Register, Memory, Stack Pointers Arithmetic Operands Instructions Objectives

3. Procedures Why? Syntax PROC / ENDP CALL / RET Operation CALL types Intrasegment  IP relative  Indirect Intersegment  Direct  Indirect RET types

4. Procedures Nesting and Single Module Programs Example and stack operation Context Save / Restore Caller vs. procedure Course documentation requirements PUSH / POP balance and order Testing & Debugging Procedures Interface Implementation Integration

5. Multiple File Assembly/Linking Each assembly source file is assembled independently – linker then joins together. How to make it all work… EXTRN directive PUBLIC directive GLOBAL directive Segment COMBINE types Addressability issues TASM/TLINK commandscommands Example source code wk6main.asm wk6proc.asm wk6main.asmwk6proc.asm

6. Parameter Passing Register Passing Memory Passing Using Pointer Parameters Example Stack Passing Reentrant procedures Using a stack frame Parameters Local variables Example ENTER / LEAVE

7. Arithmetic Operands Unsigned Binary Integers  Byte  Word  Double-word Signed Binary Integers  Byte  Word  Double-word Unpacked BCD Packed BCD Arithmetic Overflow Multi-precision Operations

8. Unsigned Arithmetic Operations Most also used for signed arithmetic MnemonicOperandsFunction OSZAPC ADD dst, srcAddition  ADC dst, srcAdd with carry  INC dstIncrement by 1  - SUB dst, srcSubtraction  SBB dst, srcSubtract with borrow  DEC dstDecrement by 1  - CMP dst,srcCompare  MUL srcUnsigned multiplication  ????  DIV srcUnsigned division??????

9. Signed Arithmetic Operations All signed numbers represented in 2’s- complement format Can use the general math operations discussed for unsigned numbers, plus some specific signed arithmetic instructions… MnemonicOperandsFunction OSZAPC NEG dstNegate------ CBW noneConvert byte to word???  ?  CWD noneConvert word to double word ------ IMUL srcInteger multiplication  ????  IDIV srcInteger division??????

10. BCD Arithmetic Operations Unpacked BCD Packed BCD Mnemonic Use Inherent Operands Function OSZAPC AAA ASCII adjust for addition???  ?  AAS ASCII adjust for subtraction???  ?  AAM ASCII adjust for multiplication?  ?  ? AAD ASCII adjust for division?  ?  ? DAA Decimal adjust for addition  DAS Decimal adjust for subtraction 

11. Numeric Conversions BCD  Binary Convenient relationship between bit groups and digits Hexadecimal  binary is similar, but have to account for 0-9 and A-F (a-f) Binary  Decimal No convenient relationship between bit groups and digits Repeated subtraction Division/modulus

12. Wrapping Up Exam 1 will be held on Thursday, October 18, 2001 from 7:15 to 8:45 PM in 132 Noland

13. .186 assume cs:code, ss:stck, ds:data extrn MyProc:PROC public gVar stcksegment db 256 dup (?);256 byte stack toslabel word;top of stack stck ends datasegment public gVardb 0;define variable dataends codesegment public main:mov ax, data;DS addressability mov ds, ax mov ax, stck;SS addressability mov ss, ax mov sp, offset tos;initialize sp main_loop: call MyProc;call external proc jmp main_loop codeends endmain;code entry point wk6main.asmwk6main.asm

14. wk6proc.asmwk6proc.asm.186 assume cs:code, ds:data global MyProc:PROC global gVar:BYTE datasegment public ;empty segment for assume directive dataends codesegment public ;need procedure comment header! MyProcproc inc gVar ret MyProcendp codeends end ;don't define another code entry point! wk6proc.asmwk6proc.asm

15. TASM/TLINK Commands tasm /l /zi wk6main tasm /l /zi wk6proc tlink /v wk6main wk6proc (the executable file will have the same name as the first object file, so in this case the linker will create wk6main.exe) tlink /v wk6main wk6proc, wk6 (the executable file will be named wk6.exe)