ECE291 Computer Engineering II Lecture 6

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ECE291Computer Engineering IILecture 6

• Josh Potts
• University of Illinois at Urbana- Champaign

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Outline

• Program organization
• Debugging hints
• MASM directives

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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

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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...

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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

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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

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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 CSCSEG DESCSEG SSSTACK

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Example Program Structure

• TITLE ECE291MPXXX
• 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 dspmsgnear, dspoutnear, kbdinnear
• extrn rsavenear, rrestnear, binascnear
  

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Example Program Structure (cont.)

• LIBMPXXX Routines (Your code will replace
  calls to these functions)
• extrn LibKbdHandlernear
• extrn LibMouseHandlernear
• extrn LibDisplayResultnear
• extrn MPXXXXITnear
• Stack
  
• stkseg segment stack
  STACK SEGMENT
• db 64 dup ('STACK ') 648
  512 Bytes of Stack
• stkseg ends
• Begin Code/Data
  
• cseg segment public 'CODE'
  CODE SEGMENT
• assume cscseg, dscseg, ssstkseg,
  esnothing

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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

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Example Program Structure (cont.)

• Procedures
  
• KbdHandler PROC NEAR
• ltYour code heregt
• KbdHandler ENDP
• MouseHandler PROC NEAR
• ltYour code heregt
• MouseHandler ENDP
• DisplayResult PROC NEAR
• ltYour code heregt
• DisplayResult ENDP

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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
• lthere comes your main proceduregt
• CALL MPXXXXIT Exit
  to DOS
• MAIN ENDP
• CSEG ENDS
• END MAIN