path: root/baremetal/ex2.hex

# Test out the video mode by filling in the screen with pixels.
#
# To run, first prepare a realistically sized disk image:
#   dd if=/dev/zero of=disk.img count=20160  # 512-byte sectors, so 10MB
# Load the program on the disk image:
#   cat baremetal/boot.hex baremetal/ex2.hex  |./bootstrap run apps/hex  > a.bin
#   dd if=a.bin of=disk.img conv=notrunc
# To run:
#   qemu-system-i386 disk.img
# Or:
#   bochs -f baremetal/boot.bochsrc  # boot.bochsrc loads disk.img
#
# Expected output:
#   html/baremetal.png

# main:  (address 0x9000)

# ecx <- LFB
8b  # copy *rm32 to r32
  0d  # 00/mod/indirect 001/r32/ecx 101/rm32/use-disp32
  28 7f 00 00 # disp32 [label]

# eax <- LFB + 0xbffff (1024*768 - 1)
8d  # copy-address rm32 to r32
  81  # 10/mod/*+disp32 000/r32/eax 001/rm32/ecx
  ff ff 0b 00  # disp32

# $loop:
# if (eax < ecx) break
39  # compare rm32 with r32
  c8  # 11/mod/direct 001/r32/ecx 000/rm32/eax
7c 05  # break if < [label]
# *eax <- al
88  # copy r8 to m8 at r32
  00  # 00/mod/indirect 000/r8/AL 000/rm32/eax
48  # decrement eax
eb f7  # loop to -9 bytes [label]

# $break:
e9 fb ff ff ff  # hang indefinitely

# vim:ft=subx