59 lines
1.7 KiB
Plaintext
59 lines
1.7 KiB
Plaintext
# Draw pixels in response to keyboard events, starting from the top-left
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# and in raster order.
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#
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# To run, first prepare a realistically sized disk image:
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# dd if=/dev/zero of=disk.img count=20160 # 512-byte sectors, so 10MB
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# Load the program on the disk image:
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# cat baremetal/boot.hex baremetal/ex3.hex |./bootstrap run apps/hex > a.bin
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# dd if=a.bin of=disk.img conv=notrunc
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# To run:
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# qemu-system-i386 disk.img
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# Or:
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# bochs -f baremetal/boot.bochsrc # boot.bochsrc loads disk.img
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# main: (address 0x9000)
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# eax <- LFB
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8b # copy *rm32 to r32
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05 # 00/mod/indirect 000/r32/eax 101/rm32/use-disp32
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28 81 00 00 # disp32 [label]
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# var read index/ecx: byte = 0
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31 c9 # ecx <- xor ecx; 11/direct 001/r32/ecx 001/rm32/ecx
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# $loop:
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# CL = *read index
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8a # copy m8 at r32 to r8
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0d # 00/mod/indirect 001/r8/cl 101/rm32/use-disp32
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cc 7d 00 00 # disp32 [label]
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# CL = *(keyboard buffer + ecx)
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8a # copy m8 at r32 to r8
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89 # 10/mod/*+disp32 001/r8/cl 001/rm32/ecx
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d0 7d 00 00 # disp32 [label]
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# if (CL == 0) loop (spin loop)
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80
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f9 # 11/mod/direct 111/subop/compare 001/rm8/CL
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00 # imm8
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74 ef # loop -17 [label]
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# offset 0x19:
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# otherwise increment read index
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fe # increment byte
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05 # 00/mod/indirect 000/subop/increment 101/rm32/use-disp32
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cc 7d 00 00 # disp32 [label]
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# clear top nibble of index (keyboard buffer is circular)
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80 # and byte
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25 # 00/mod/indirect 100/subop/and 101/rm32/use-disp32
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cc 7d 00 00 # disp32 [label]
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0f # imm8
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# print a pixel in fluorescent green
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c6 # copy imm8 to m8 at rm32
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00 # 00/mod/indirect 000/subop 000/rm32/eax
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31 # imm32
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40 # increment eax
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eb dc # loop -36 [label]
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# $break:
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e9 fb ff ff ff # hang indefinitely
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# vim:ft=subx
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