diff options
Diffstat (limited to 'baremetal')
| -rw-r--r-- | baremetal/boot.hex | 43 |
1 files changed, 30 insertions, 13 deletions
diff --git a/baremetal/boot.hex b/baremetal/boot.hex index 50fdb334..c05a3f19 100644 --- a/baremetal/boot.hex +++ b/baremetal/boot.hex @@ -74,21 +74,43 @@ # calls, so we don't need to initialize the stack. # 0e: - # load some sectors from disk + # load 62 sectors from disk into addresses [0x7e00, 0xfa00) b4 02 # ah <- 2 # read sectors from disk +# 10: # dl comes conveniently initialized at boot time with the index of the device being booted b5 00 # ch <- 0 # cylinder 0 b6 00 # dh <- 0 # track 0 b1 02 # cl <- 2 # second sector, 1-based - b0 80 # al <- 128 # number of sectors to read; TODO - all sectors might need to be in a single track on real hardware (so 63 sectors at most including the boot sector) + b0 3e # al <- 62 # number of sectors to read # address to write sectors to = es:bx = 0x7e00, contiguous with boot segment bb 00 00 # bx <- 0 8e c3 # es <- bx bb 00 7e # bx <- 0x7e00 [label] +# 20: cd 13 # int 13h, BIOS disk service - 0f 82 8a 00 # jump-if-carry disk-error [label] - + 0f 82 8a 00 # jump-if-carry disk_error [label] # 26: + # load 63 sectors from disk into addresses [0xfa00, 0x17800) + b4 02 # ah <- 2 # read sectors from disk + b5 00 # ch <- 0 # cylinder 0 + b6 01 # dh <- 1 # track 1 + b1 01 # cl <- 1 # first sector, 1-based + b0 3f # al <- 63 # number of sectors to read +# 30: + # "Addressing of Buffer should guarantee that the complete buffer is inside + # the given segment, i.e. ( BX + size_of_buffer ) <= 10000h." + # https://en.wikipedia.org/wiki/INT_13H#INT_13h_AH=02h:_Read_Sectors_From_Drive + bb 00 fa # bx <- 0xfa00 [label] + 8e c3 # es <- bx + bb 00 00 # bx <- 0 + cd 13 # int 13h, BIOS disk service + 0f 82 72 00 # jump-if-carry disk_error [label] +# 3e: + # reset es + bb 00 00 # bx <- 0 + 8e c3 # es <- bx + +# 43: # undo the A20 hack: https://en.wikipedia.org/wiki/A20_line # this is from https://github.com/mit-pdos/xv6-public/blob/master/bootasm.S # seta20.1: @@ -99,7 +121,7 @@ b0 d1 # al <- 0xd1 e6 64 # port 0x64 <- al -# 30: +# 4d: # seta20.2: e4 64 # al <- port 0x64 a8 02 # set zf if bit 1 (second-least significant) is not set @@ -108,7 +130,7 @@ b0 df # al <- 0xdf e6 64 # port 0x64 <- al -# 3a: +# 57: # adjust video mode b4 4f # ah <- 4f (VBE) b0 02 # al <- 02 (set video mode) @@ -117,7 +139,7 @@ # fallback mode: 0x0101 (640x480x256) cd 10 # int 10h, Vesa BIOS extensions -# 43: +# 60: # load information for the (hopefully) current video mode # mostly just for the address to the linear frame buffer b4 4f # ah <- 4f (VBE) @@ -126,7 +148,7 @@ bf 00 7f # di <- 0x7f00 (video mode info) [label] cd 10 -# 4f: +# 6c: # switch to 32-bit mode 0f 01 16 # lgdt 00/mod/indirect 010/subop 110/rm/use-disp16 a0 7c # *gdt_descriptor [label] @@ -135,11 +157,6 @@ 0f 22 c0 # cr0 <- eax ea e0 7c 08 00 # far jump to initialize_32bit_mode after setting cs to the record at offset 8 in the gdt (gdt_code) [label] -# padding -# 63: - 00 00 00 00 00 00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 - ## GDT: 3 records of 8 bytes each # 80: |