ECE 353 Introduction to Microprocessor Systems Michael J. Schulte Week 6

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

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

Procedures Nesting and Single Module Programs Example and stack operation Context Save / Restore Protocols Course documentation requirements PUSH / POP balance and ordering  Keep it simple and uniform Testing & Debugging Procedures Software Interface Implementation Integration

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 good versionbetter version good versionbetter version

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

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

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??????

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??????

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 

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

Exercise Write a procedure mul32 to do a 32-bit multiplication with a 32-bit result. Operands are to be passed using a standard stack frame, ensuring that they are in little-endian form in memory when they are on the stack. Any temporary storage must be allocated on the stack. Return the result in DX:AX.

Wrapping Up Reading for next week Chapter 10,

;need file header!.186 assume cs:code, ss:stck stcksegment db 256 dup (?);256 byte stack toslabel word stck ends codesegment ;need procedure header! procedure1proc callprocedure2 ret procedure1endp ;need procedure header! procedure2proc ret procedure2endp start:movax, stck;SS addressability movss, ax movsp, offset tos;initialize sp main_loop: callprocedure1 jmp main_loop codeends endstart wk6ex1.asmwk6ex1.asm

.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

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

globals.inc ; Filename: globals.inc ; Author: ECE 353 Staff ; Description: Week 6 example of include file global MyProc:PROC global gVar:BYTE

.186 assume cs:code, ss:stck, ds:data include globals.inc 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 wk6main1.asmwk6main1.asm

wk6proc1.asmwk6proc1.asm.186 assume cs:code, ds:data include globals.inc 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!

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) OR tlink /v wk6main wk6proc, wk6 (the executable file will be named wk6.exe)

Pointer Parameter Exercise i. Define a variable length data structure where the first word is the number of words of data that follow. ii. Write a procedure that finds the maximum value in the array, assuming that the data is unsigned. iii. Assume that the starting address of the data structure is passed in BX. iv. Return the result in AX. Assume addressability and stack initialization have been correctly handled.

Stack Frame Example Write code for a main program that uses a stack frame to call a procedure Update - parameter words X,Y, data are to be pushed in that order. Draw a word-wide stack, indicating the objects placed on it by the caller. Write a stub Update procedure - assume the procedure must use 2 words of local variables Set up the stack frame, Show how you would access the 3 passed parameters, Show how you would access the 2 local variable words, Clean up the stack frame, and Return. Update the stack diagram, indicating how it is used/allocated by the procedure.