Introduction to Computer Systems

Tutorial / Laboratory 06 - procedures

Week 7

Preparation [1 Marks]

1. Read over the rPeANUt manual in relation to the frame buffer and graphics.
2. Review the your strengths and weaknesses for this course (make a note of them).

Lab [4 Marks]

1. Write a program in rPeANUt that fills the graphics display with white and then halts. Using the command line count how many instructions it uses (compare with others in the lab). Also dump the frame buffer to a text file (using the -dump option) and check it is the same as whitescreen.dump. Use the "diff" command.
2. Write a procedure that sets a particular pixel of the graphics display to white. Use the below for the signature/stack frame for the method.

   ; setpixel - set a pixel to be white
   ; stack frame :
   ;  return address #0
   ;  y #-1
   ;  x #-2
   ; "pixel (x,y) will be bit x%32 of the word at 
   ; address 0x7C40 + 6*y + x/32" from spec
   

   Test your approach with a program that set particular pixels.
3. Include your setpixel method into the below program.

   ;  for (i = 0; i < 100; i++) {
   ;    setpixel((rand())%192,(rand())%160);
   ;  }
   
   0x0100 :   jump loopbool
   loop:      push R0   ; work out x pixel
              call rand
              pop R0
              load #192 R1
              mod R0 R1 R0
              push R0 
   
              push R0   ; work out y pixel
              call rand
              pop R0
              load #160 R1
              mod R0 R1 R0
              push R0 
              call setpixel ; draw the pixel 
              pop R0
              pop R0
              load loopcount R1
              add R1 ONE R1
              store R1 loopcount 
   loopbool : load #100 R0
              load loopcount R1
              sub R0 R1 R1
              jumpnz R1 loop
              halt
   
   loopcount : block 1
   mask : block #0x7fffffff ; we need this mask so the random number is positive
   
   ; rand - generate psudo random numbers.
   ; this uses Linear Congruential Generator see http://en.wikipedia.org/wiki/Linear_congruential_generator
   ; stack frame :
   ;   return address #0
   ;   return random value #-1
   rand : load aval R0
          load rval R1
          mult R0 R1 R1
          load cval R0
          add R1 R0 R1
          store R1 rval
          rotate #12 R1 R1
          load mask R0
          and R0 R1 R1
          store R1 #-1 SP
          return
   rval : block #0  ; this stores the current random 
   aval : block #1664525
   cval : block #1013904223
   
   

   Now when you run the program you should see a random cloud of pixels. Use the command line and the -dump option to check that what you have is the same as what is expected. cloud.dump