diff options
| author | Kartik K. Agaram <vc@akkartik.com> | 2021-08-29 08:40:52 -0700 |
|---|---|---|
| committer | Kartik K. Agaram <vc@akkartik.com> | 2021-08-29 11:21:09 -0700 |
| commit | c5f8415e0327124a7a9fed12b524390ddf417f83 (patch) | |
| tree | 84636fc30a127340f30214ce8b39ec12fa53baba /boot.subx | |
| parent | 0e2a9ad93d96be55a4df3f509a33df882dae81ef (diff) | |
| download | mu-c5f8415e0327124a7a9fed12b524390ddf417f83.tar.gz | |
retreat to 640KB
Diffstat (limited to 'boot.subx')
| -rw-r--r-- | boot.subx | 18 |
1 files changed, 3 insertions, 15 deletions
diff --git a/boot.subx b/boot.subx index 6bed6fe2..7d4e174b 100644 --- a/boot.subx +++ b/boot.subx @@ -164,13 +164,13 @@ cd/syscall 0x13/imm8/bios-disk-services 0f 82/jump-if-carry disk_error/disp16 - # load two more tracks of disk into addresses [0x76000, 0x85c00) + # load one final track of disk into addresses [0x76000, 0x7de00) b4/copy-to-ah 2/imm8/read-drive # dl comes conveniently initialized at boot time with the index of the device being booted b5/copy-to-ch 0/imm8/cylinder b6/copy-to-dh 0xe/imm8/head # <==== b1/copy-to-cl 1/imm8/sector # 1-based - b0/copy-to-al 0x7e/imm8/num-sectors # 2*63 = 126 + b0/copy-to-al 0x3f/imm8/num-sectors=63 # address to write sectors to = es:bx = 0x56800, contiguous with boot segment bb/copy-to-bx 0x7600/imm16 # <==== 8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es @@ -178,19 +178,7 @@ cd/syscall 0x13/imm8/bios-disk-services 0f 82/jump-if-carry disk_error/disp16 - # load two more tracks of disk into addresses [0x85c00, 0x95800) - b4/copy-to-ah 2/imm8/read-drive - # dl comes conveniently initialized at boot time with the index of the device being booted - b5/copy-to-ch 0/imm8/cylinder - b6/copy-to-dh 0x11/imm8/head # <==== - b1/copy-to-cl 1/imm8/sector # 1-based - b0/copy-to-al 0x7e/imm8/num-sectors # 2*63 = 126 - # address to write sectors to = es:bx = 0x56800, contiguous with boot segment - bb/copy-to-bx 0x85c0/imm16 # <==== - 8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es - bb/copy-to-bx 0/imm16 - cd/syscall 0x13/imm8/bios-disk-services - 0f 82/jump-if-carry disk_error/disp16 + ### Can't load more tracks without clobbering BIOS code. To load more code we'll need a new compilation strategy. # reset es bb/copy-to-bx 0/imm16 |