ECE 353 Introduction to Microprocessor Systems

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

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

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 • Protocols • Course documentation requirements • PUSH / POP balance and ordering • Keep it simple and uniform • Testing & Debugging Procedures • Software 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 commands • Example source code • good versionbetter version

6. Parameter Passing • Register Passing • Memory Passing • Using Pointer Parameters • Exercise • 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

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…

10. BCD Arithmetic Operations • Unpacked BCD • Packed BCD

11. 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

12. 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.

13. Wrapping Up • Reading for next week • Chapter 10, 10.1-10.6

14. ;need file header! .186 assume cs:code, ss:stck stck segment db 256 dup (?) ;256 byte stack tos label word stck ends code segment ;need procedure header! procedure1 proc call procedure2 ret procedure1 endp ;need procedure header! procedure2 proc ret procedure2 endp start: mov ax, stck ;SS addressability mov ss, ax mov sp, offset tos ;initialize sp main_loop: call procedure1 jmp main_loop code ends end start wk6ex1.asm

15. .186 assume cs:code, ss:stck, ds:data extrn MyProc:PROC public gVar stck segment db 256 dup (?) ;256 byte stack tos label word ;top of stack stck ends data segment public gVar db 0 ;define variable data ends code segment 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 code ends end main ;code entry point wk6main.asm

16. wk6proc.asm .186 assume cs:code, ds:data global MyProc:PROC global gVar:BYTE data segment public ;empty segment for assume directive data ends code segment public ;need procedure comment header! MyProc proc inc gVar ret MyProc endp code ends end ;don't define another code entry point! wk6proc.asm

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

18. .186 assume cs:code, ss:stck, ds:data include globals.inc stck segment db 256 dup (?) ;256 byte stack tos label word ;top of stack stck ends data segment public gVar db 0 ;define variable data ends code segment 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 code ends end main ;code entry point wk6main1.asm

19. .186 assume cs:code, ds:data include globals.inc data segment public ;empty segment for assume directive data ends code segment public ;need procedure comment header! MyProc proc inc gVar ret MyProc endp code ends end ;don't define another code entry point! wk6proc1.asm

20. 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)

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

22. 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.