diff options
Diffstat (limited to 'boot.subx')
| -rw-r--r-- | boot.subx | 38 |
1 files changed, 26 insertions, 12 deletions
diff --git a/boot.subx b/boot.subx index a06cec44..31d79d4f 100644 --- a/boot.subx +++ b/boot.subx @@ -136,6 +136,20 @@ cd/syscall 0x13/imm8/bios-disk-services 0f 82/jump-if-carry disk_error/disp16 + # load two more tracks of disk into addresses [0x56800, 0x66400) + 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 0xa/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 0x5680/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 + # reset es bb/copy-to-bx 0/imm16 8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es @@ -162,7 +176,7 @@ # We can't refer to the label directly because SubX doesn't do the right # thing for lgdt, so rather than make errors worse in most places we instead # pin gdt_descriptor below. - 0f 01 2/subop/lgdt 0/mod/indirect 6/rm32/use-disp16 0x7ce0/disp16/gdt_descriptor + 0f 01 2/subop/lgdt 0/mod/indirect 6/rm32/use-disp16 0x7de0/disp16/gdt_descriptor # enable paging 0f 20/<-cr 3/mod/direct 0/rm32/eax 0/r32/cr0 66 83 1/subop/or 3/mod/direct 0/rm32/eax 1/imm8 # eax <- or 0x1 @@ -170,7 +184,7 @@ # far jump to initialize_32bit_mode that sets cs to offset 8 in the gdt in the process # We can't refer to the label directly because SubX doesn't have syntax for # segment selectors. So we instead pin initialize_32bit_mode below. - ea/jump-far-absolute 0x00087d00/disp32 # address 0x7d00 in offset 8 of the gdt + ea/jump-far-absolute 0x00087e00/disp32 # address 0x7e00 in offset 8 of the gdt disk_error: # print 'D' to top-left of screen to indicate disk error @@ -187,7 +201,7 @@ disk_error: } ## GDT: 3 records of 8 bytes each -== data 0x7ce0 +== data 0x7de0 gdt_descriptor: 0x17/imm16 # final index of gdt = size of gdt - 1 gdt_start/imm32/start @@ -212,9 +226,15 @@ gdt_start: 00 # base[24:32] # gdt_end: +== boot-sector-marker 0x7dfe +# final 2 bytes of boot sector +55 aa + +## sector 2 onwards loaded by load_disk, not automatically on boot + ## 32-bit code from this point -== code 0x7d00 +== code 0x7e00 initialize_32bit_mode: 66 b8/copy-to-ax 0x10/imm16 # offset 16 from gdt_start 8e/->seg 3/mod/direct 0/rm32/ax 3/r32/ds @@ -229,7 +249,7 @@ initialize_32bit_mode: # We can't refer to the label directly because SubX doesn't do the right # thing for lidt, so rather than make errors worse in most places we instead # pin idt_descriptor below. - 0f 01 3/subop/lidt 0/mod/indirect 5/rm32/use-disp32 0x7e00/disp32/idt_descriptor + 0f 01 3/subop/lidt 0/mod/indirect 5/rm32/use-disp32 0x7f00/disp32/idt_descriptor # For now, not bothering reprogramming the IRQ to not conflict with software # exceptions. @@ -259,13 +279,7 @@ initialize_32bit_mode: e9/jump Entry/disp32 -== boot-sector-marker 0x7dfe -# final 2 bytes of boot sector -55 aa - -## sector 2 onwards loaded by load_disk, not automatically on boot - -== data 0x7e00 +== data 0x7f00 idt_descriptor: ff 03 # final index of idt = size of idt - 1 idt_start/imm32/start |