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100 lines
3.0 KiB
NASM
100 lines
3.0 KiB
NASM
// This file is part of www.nand2tetris.org
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// and the book "The Elements of Computing Systems"
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// by Nisan and Schocken, MIT Press.
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// File name: projects/4/Fill.asm
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// Runs an infinite loop that listens to the keyboard input.
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// When a key is pressed (any key), the program blackens the screen,
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// i.e. writes "black" in every pixel. When no key is pressed,
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// the screen should be cleared.
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// excuse excessive comments here again..
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// run test with cmd line, otherwise it takes forever
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// later note: web IDE seems to render screen, local tester does not.
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// code duplication- we need to write the same code for filling black and white, but this feels wrong (code reuse)
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(LOOP) // main loop
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// check kb input
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@KBD // sel kb
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D=M // load kb value to data
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@FILL_BLACK // sel fill black
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D;JNE // jump if key pressed (jump not equal? non-zero)
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// jump to fill white if no key pressed
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@FILL_WHITE // sel fill white
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0;JMP // jump unconditionally
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(FILL_BLACK) // fill screen with black
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// init count and pointer
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// screen = 512x256 pixels = 131072 pixels total
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// each word holds 16 pixels, so 131072/16 = 8192 words
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@8192 // sel value for count (8192)
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D=A // load 8192 to data
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@count // sel count var
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M=D // set count = 8192
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@SCREEN // sel screen start
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D=A // load screen address to data
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@pointer // sel pointer var
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M=D // set pointer = screen start
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(BLACK_LOOP) // loop for filling black
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// check if count = 0
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@count // sel count
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D=M // load count to data
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@LOOP // sel main loop
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D;JEQ // jump to main if done
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// set word to -1 (black)
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@pointer // sel pointer
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A=M // set address to pointer value
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M=-1 // set screen word to black
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// inc pointer
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@pointer // sel pointer
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M=M+1 // inc pointer
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// dec count
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@count // sel count
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M=M-1 // dec count
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// jump back to black loop
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@BLACK_LOOP // sel black loop
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0;JMP // jump back to loop
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(FILL_WHITE) // fill screen with white
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// init count and pointer
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// screen = 512x256 pixels = 131072 pixels total
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// each word holds 16 pixels, so 131072/16 = 8192 words
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@8192 // sel value for count (8192)
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D=A // load 8192 to data
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@count // sel count var
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M=D // set count = 8192
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@SCREEN // sel screen start
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D=A // load screen address to data
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@pointer // sel pointer var
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M=D // set pointer = screen start
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(WHITE_LOOP) // loop for filling white
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// check if count = 0
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@count // sel count
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D=M // load count to data
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@LOOP // sel main loop
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D;JEQ // jump to main if done
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// set word to 0 (white)
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@pointer // sel pointer
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A=M // set address to pointer value
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M=0 // set screen word to white
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// inc pointer
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@pointer // sel pointer
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M=M+1 // inc pointer
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// dec count
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@count // sel count
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M=M-1 // dec count
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// jump back to white loop
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@WHITE_LOOP // sel white loop
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0;JMP // jump back to loop
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