diff options
| -rw-r--r-- | apps/boot.hex | 93 |
1 files changed, 69 insertions, 24 deletions
diff --git a/apps/boot.hex b/apps/boot.hex index 0bf0874f..dad4a098 100644 --- a/apps/boot.hex +++ b/apps/boot.hex @@ -1,7 +1,8 @@ # Bootable image that: # - loads more sectors past the first boot sector (using BIOS primitives) # - switches to 32-bit mode (giving up access to BIOS primitives) -# - as an example program, prints a letter from the second sector to the top-left of the screen (by writing to memory-mapped VGA memory) +# - sets up a handler for keyboard events +# - as an example program, prints alphabets to the top-left position on screen (by writing to memory-mapped VGA memory) as they're typed # # If the initial load fails, it prints 'D' to the top-left of the screen and # halts. @@ -32,7 +33,8 @@ # to the address range [0x7c00, 0x7e00) # offset 00 (address 0x7c00): - fa # cli # TODO: don't forget to reenable interrupts in a real program + # disable interrupts for this initialization + fa # cli # initialize segment registers # this isn't always needed, but is considered safe not to assume @@ -46,7 +48,7 @@ # We don't read or write the stack before we get to 32-bit mode. No function # calls, so we don't need to initialize the stack. -# 0d: +# 0e: # load more sectors from disk b4 02 # ah <- 2 # read sectors from disk # dl comes conveniently initialized at boot time with the index of the device being booted @@ -166,11 +168,18 @@ e9 fb ff # loop forever 8e c0 # es <- ax 8e e0 # fs <- ax 8e e8 # gs <- ax - e9 2d 00 00 00 # jump to 0x7d00 + + # load interrupt handlers + 0f 01 1e # lidt 00/mod/indirect 011/subop 110/rm32/TODO + 00 7f # *idt_descriptor + + # initialization is done; enable interrupts + fb + e9 27 00 00 00 # jump to 0x7d00 # padding -# d3: - 00 00 00 00 00 00 00 00 00 00 00 00 00 +# d9: + 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 00 00 00 00 00 00 00 00 00 00 @@ -194,6 +203,9 @@ e9 fb ff ff ff # loop forever # padding # 111: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + +# 120: + 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 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 @@ -215,24 +227,57 @@ e9 fb ff ff ff # loop forever ## sector 2 # not loaded on boot; loaded by load_disk -# offset 200 (address 0x7e00): -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 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 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 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 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 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 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 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 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 00 00 00 00 00 00 00 00 00 00 00 +# offset 200 (address 0x7e00): interrupt descriptor table +# 32 entries * 8 bytes each = 256 bytes (0x100) +# idt_start: +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 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 00 00 00 00 00 00 +00 00 00 00 00 00 00 00 + +# offset 9: keyboard, following https://alex.dzyoba.com/blog/os-interrupts + 20 7d # offset[0:16] + 08 00 # segment selector (gdt_code) + 00 # unused + 8e # 1/p 00/dpl 0 1110/type/32-bit-interrupt-gate + 00 00 # offset[16:32] + +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 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 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 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 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 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 00 00 +# idt_end: + +# offset 300 (address 0x7f00): +# idt_descriptor: + ff 00 # idt_end - idt_start - 1 + 00 7e 00 00 # start = idt_start + +# padding + 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 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 |