ECE 353 Introduction to Microprocessor Systems Week 6

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

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

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

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

Multiple File Assembly/Linking Each assembly source file is assembled independently – linker then joins together. How to make it all work… n n n EXTRN directive PUBLIC directive GLOBAL directive Segment COMBINE types Addressability issues TASM/TLINK commands Example source code n wk 6 main. asm wk 6 proc. asm

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

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

Unsigned Arithmetic Operations Most also used for signed arithmetic Mnemonic Operands Function O S Z A P C ADD dst, src Addition ADC INC dst, src Add with carry dst Increment by 1 - SUB SBB DEC CMP MUL DIV dst, src Subtraction dst, src Subtract with borrow dst Decrement by 1 - dst, src Compare src Unsigned multiplication ? ? src Unsigned division ? ? ?

Signed Arithmetic Operations All signed numbers represented in 2’scomplement format Can use the general math operations discussed for unsigned numbers, plus some specific signed arithmetic instructions… Mnemonic Operands Function O S Z A P C NEG dst Negate - - - CBW CWD none Convert byte to word ? ? ? ? none Convert word to double word - - - IMUL IDIV src Integer multiplication ? ? src Integer division ? ? ?

BCD Arithmetic Operations Unpacked BCD Packed BCD AAA AAS AAM AAD DAA DAS Use Inherent Operands Mnemonic Function O S Z A P C ASCII adjust for addition ? ? ? ? ASCII adjust for subtraction ? ? ? ? ASCII adjust for multiplication ? ? ? ASCII adjust for division ? ? ? Decimal adjust for addition Decimal adjust for subtraction

Numeric Conversions BCD Binary n n 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 n n n No convenient relationship between bit groups and digits Repeated subtraction Division/modulus

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

w k 6 m a i n. a s m . 186 assume cs: code, ss: stck, ds: data extrn My. Proc: PROC public g. Var stck tos stck segment db 256 dup (? ) label word ends ; 256 byte stack ; top of stack data g. Var data segment public db 0 ends ; define variable code segment public main: mov ax, data mov ds, ax mov ax, stck mov ss, ax mov sp, offset tos main_loop: call My. Proc jmp main_loop code ends end main ; DS addressability ; SS addressability ; initialize sp ; call external proc ; code entry point

w w kk 66 pp rr oo c. c. aa ss m m . 186 assume cs: code, ds: data global My. Proc: PROC global g. Var: BYTE data segment public ; empty segment for assume directive data ends code segment public ; need procedure comment header! My. Proc proc inc g. Var ret My. Proc endp code ends end ; don't define another code entry point!

TASM/TLINK Commands tasm /l /zi wk 6 main tasm /l /zi wk 6 proc tlink /v wk 6 main wk 6 proc (the executable file will have the same name as the first object file, so in this case the linker will create wk 6 main. exe) tlink /v wk 6 main wk 6 proc, wk 6 (the executable file will be named wk 6. exe)