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ECE291 Computer Engineering II Lecture 6

ECE291 Computer Engineering II Lecture 6. Josh Potts University of Illinois at Urbana- Champaign. Outline. Program organization Debugging hints MASM directives. Program Organization.

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ECE291 Computer Engineering II Lecture 6

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  1. ECE291Computer Engineering IILecture 6 Josh Potts University of Illinois at Urbana- Champaign

  2. Outline • Program organization • Debugging hints • MASM directives ECE291

  3. Program Organization • Create block structure and/or pseudocode on paper to get a clear concept of program control flow and data structures • Break the total program into logical procedures/macros • Use jumps, loops, etc. where appropriate • Use descriptive names for variables • noun_type for types • nouns for variables • verbs for procedures/functions ECE291

  4. Debugging Hints • Good program organization helps • Programs do not work the first time • Strategy to find problems • Use DEBUG breakpoints to check program progress • Use COMMENT to temporarily remove sections of code • "print" statements announce milestones in program • Test values/cases • Try forcing registers/variables to test output of a procedure • Use "print" statements to display critical data • Double-check your own logic (Did you miss a special case?) • Try a different algorithm, if all else fails... ECE291

  5. MASM Directives • General • TITLE my_program.asm • Includes drive:\path\filename • Definitions • DB define byte (8bits) • DW define word (16 bits) • DD define doubleword (32 bits) • EQU names a constant • Labels ECE291

  6. MASM Directives • Macros • Instead of using procedures, which require both stack and time resources, macros are fast and flexible • Advantages: • speed; no call instruction • readability - easier to understand program function • Drawbacks - • space using the MACRO multiple times duplicates the code • tricky to debug (in particular when you have nested MACROs) • Procedures • “name” PROC NEAR/FAR • ENDP ECE291

  7. MASM Directives (cont.) • References to procedures • EXTERN “name” NEAR/FAR/BYTE/WORD • PUBLIC “ name” • Segment definition • SEGMENT “name” PUBLIC/STACK • ENDS • Segment register “Hooks” • ASSUME CS:CSEG; DES:CSEG; SS:STACK ECE291

  8. Example Program Structure TITLE ECE291:MPXXX COMMENT * In this MP you will develop program which take input from the keyboard………… * ;====== Constants ==================================================== ;ASCII values for common characters CR EQU 13 LF EQU 10 ESCKEY EQU 27 ;====== Externals ==================================================== ; -- LIB291 Routines extrn dspmsg:near, dspout:near, kbdin:near extrn rsave:near, rrest:near, binasc:near ECE291

  9. Example Program Structure (cont.) ; ==== LIBMPXXX Routines (Your code will replace calls to these functions) extrn LibKbdHandler:near extrn LibMouseHandler:near extrn LibDisplayResult:near extrn MPXXXXIT:near ;====== Stack ======================================================== stkseg segment stack ; *** STACK SEGMENT *** db 64 dup ('STACK ') ; 64*8 = 512 Bytes of Stack stkseg ends ;====== Begin Code/Data ============================================== cseg segmentpublic 'CODE' ; *** CODE SEGMENT *** assume cs:cseg, ds:cseg, ss:stkseg, es:nothing ECE291

  10. Example Program Structure (cont.) ;====== Variables ==================================================== inputValid db 0 ; 0: InputBuffer is not ready ; 1: InputBuffer is ready ;-1: Esc key pressed operandsStr db 'Operands: ','$' OutputBuffer db 16 dup(?),'$' ; Contains formatted output ; (Should be terminated with '$') MAXBUFLENGTH EQU 24 InputBuffer db MAXBUFLENGTH dup(?),'$' ; Contains one line of user input include graphData.dat ; data PUBLIC OutputBuffer, inputValid, operandsStr PUBLIC graphData ECE291

  11. Example Program Structure (cont.) ;====== Procedures ==================================================== KbdHandler PROC NEAR <Your code here> KbdHandler ENDP MouseHandler PROC NEAR <Your code here> MouseHandler ENDP DisplayResult PROC NEAR <Your code here> DisplayResult ENDP ECE291

  12. Example Program Structure (cont.) ;====== Main Procedure ================================================ MAIN PROC FAR MOV AX, CSEG ; Use common code and data segment MOV DS, AX MOV AX, 0B800h ; Use extra segment to access video screen MOV ES, AX <here comes your main procedure> CALL MPXXXXIT ; Exit to DOS MAIN ENDP CSEG ENDS END MAIN ECE291

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