diff options
| -rw-r--r-- | baremetal/boot.hex | 41 |
1 files changed, 16 insertions, 25 deletions
diff --git a/baremetal/boot.hex b/baremetal/boot.hex index f9735c9c..bf5ea9fb 100644 --- a/baremetal/boot.hex +++ b/baremetal/boot.hex @@ -100,7 +100,21 @@ 8e d0 # ss <- ax bc 00 00 # sp <- 0x0000 -# 14: + # 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: + e4 64 # al <- port 0x64 + a8 02 # set zf if bit 1 (second-least significant) is not set + 75 fa # if zf not set, goto seta20.1 (-6) + b0 d1 # al <- 0xd1 + e6 64 # port 0x64 <- al + # seta20.2: + e4 64 # al <- port 0x64 + a8 02 # set zf if bit 1 (second-least significant) is not set + 75 fa # if zf not set, goto seta20.2 (-6) + b0 df # al <- 0xdf + e6 64 # port 0x64 <- al + # load remaining sectors from first two tracks of disk into addresses [0x7e00, 0x17800) b4 02 # ah <- 2 # read sectors from disk # dl comes conveniently initialized at boot time with the index of the device being booted @@ -115,7 +129,6 @@ cd 13 # int 13h, BIOS disk service 0f 82 a3 00 # jump-if-carry disk_error [label] -# 2c: # load two more tracks of disk into addresses [0x17800, 0x27400) b4 02 # ah <- 2 # read sectors from disk # dl comes conveniently initialized at boot time with the index of the device being booted @@ -129,31 +142,11 @@ bb 00 00 # bx <- 0 cd 13 # int 13h, BIOS disk service 0f 82 9b 00 # jump-if-carry disk_error [label] + # reset es bb 00 00 # bx <- 0 8e c3 # es <- bx -# 39: - # 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: - e4 64 # al <- port 0x64 - a8 02 # set zf if bit 1 (second-least significant) is not set - 75 fa # if zf not set, goto seta20.1 (-6) - - b0 d1 # al <- 0xd1 - e6 64 # port 0x64 <- al - -# 43: - # seta20.2: - e4 64 # al <- port 0x64 - a8 02 # set zf if bit 1 (second-least significant) is not set - 75 fa # if zf not set, goto seta20.2 (-6) - - b0 df # al <- 0xdf - e6 64 # port 0x64 <- al - -# 4d: # adjust video mode b4 4f # ah <- 4f (VBE) b0 02 # al <- 02 (set video mode) @@ -162,7 +155,6 @@ # fallback mode: 0x0101 (640x480x256) cd 10 # int 10h, Vesa BIOS extensions -# 56: # load information for the (hopefully) current video mode # mostly just for the address to the linear frame buffer b4 4f # ah <- 4f (VBE) @@ -171,7 +163,6 @@ bf 00 81 # di <- 0x8100 (video mode info) [label] cd 10 -# 62: # switch to 32-bit mode 0f 01 16 # lgdt 00/mod/indirect 010/subop 110/rm/use-disp16 f8 7c # *gdt_descriptor [label] |