138 lines
1.6 KiB
NASM
138 lines
1.6 KiB
NASM
// This program does a manual fill for the entire screen
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// Loops over all rows (255) and calls
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// a screen write operation 32 times for each row
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// each row has 512 pixels = 16 * 32 bits = 32 registers
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// so each row takes 32 memory addresses in the RAM, starting from @SCREEN
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// The program uses the following:
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// @i : A counter that goes from 255->0
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// : program ends when it reaches 0
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// : this keeps track of how many rows have we covered
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// @R0: This stores the address of the first memory address for the
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// : row of the screen that we are filling right now
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// : Initialized by setting it to @SCREEN
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// @color: Stores -1, since we can't use that as a constant.
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// : Copied to D register before being written to screen
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@0
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D=A
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D=D-1
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@color
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M=D
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// Now color holds -1
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// Set counter to 255
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@255
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D=A
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@i
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M=D
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// Store our initial screen row address in D
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@SCREEN
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D=A
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// And then save it in R0
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@R0
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M=D
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// This is our screen/row writing loop
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(WRITE_COMPLETE_ROW)
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// Read color in D
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@color
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D=M
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// Load the value in R0 to A
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@R0
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A=M
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// And off we go hunting
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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A=A+1
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M=D
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// Bump A by 1 and write it to R0
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A=A+1
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D=A
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@R0
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M=D
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// Reduce i by 1
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@i
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M=M-1
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// Jump to ENDIF if @i>0
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@i
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D=M
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@ENDIF
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D;JGT
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// If i==0, jump to end
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@END
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0;JMP
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(ENDIF)
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@WRITE_COMPLETE_ROW
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0;JMP
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(END)
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@END
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0;JMP
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