ooh, timer works fine in isolation
Acknowledging the interrupt is necessary.
This commit is contained in:
Kartik K. Agaram
parent
f25b8e6e41
commit
5616691621
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@ -0,0 +1,416 @@
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# Example bootloader that handles just the timer interrupt.
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#
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# Code for the first few disk sectors that all programs in this directory need:
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# - load sectors past the first (using BIOS primitives) since only the first is available by default
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# - if this fails, print 'D' at top-left of screen and halt
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# - initialize a minimal graphics mode
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# - switch to 32-bit mode (giving up access to BIOS primitives)
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# - set up a handler for keyboard events
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# - jump to start of program
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# Code in this file needs to be more deliberate about the SubX facilities it
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# uses:
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# - sigils only support 32-bit general-purpose registers, so don't work with segment registers or 16-bit or 8-bit registers
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# - metadata like rm32 and r32 can sometimes misleadingly refer to only the bottom 16 bits of the register; pay attention to the register name
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#
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# While most of Mu is thoroughly tested, this file is not. I don't yet
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# understand hardware interfaces well enough to explain to others.
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# Memory map of a Mu computer:
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# code: currently 4 tracks loaded from the primary disk to [0x00007c00, 0x00048600)
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# stack: grows down from 0x02000000 to 0x01000000
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# heap: [0x02000000, 0x08000000)
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# see 120allocate.subx; Qemu initializes with 128MB RAM by default
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# Consult https://wiki.osdev.org/Memory_Map_(x86) before modifying any of
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# this. And don't forget to keep *stack-debug.subx in sync.
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== code
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## 16-bit entry point: 0x7c00
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# Upon reset, the IBM PC:
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# - loads the first sector (512 bytes)
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# from some bootable image (look for the boot-sector-marker further down this file)
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# to the address range [0x7c00, 0x7e00)
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# - starts executing code at address 0x7c00
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fa/disable-interrupts
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# initialize segment registers
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b8/copy-to-ax 0/imm16
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8e/->seg 3/mod/direct 0/rm32/ax 3/r32/ds
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8e/->seg 3/mod/direct 0/rm32/ax 0/r32/es
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8e/->seg 3/mod/direct 0/rm32/ax 4/r32/fs
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8e/->seg 3/mod/direct 0/rm32/ax 5/r32/gs
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# Temporarily initialize stack to 0x00070000 in real mode.
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# We don't read or write the stack before we get to 32-bit mode, but BIOS
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# calls do. We need to move the stack in case BIOS initializes it to some
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# low address that we want to write code into.
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b8/copy-to-ax 0x7000/imm16
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8e/->seg 3/mod/direct 0/rm32/ax 2/r32/ss
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bc/copy-to-esp 0/imm16
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# undo the A20 hack: https://en.wikipedia.org/wiki/A20_line
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# this is from https://github.com/mit-pdos/xv6-public/blob/master/bootasm.S
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{
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e4/read-port-into-al 0x64/imm8
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a8/test-bits-in-al 0x02/imm8 # set zf if bit 1 (second-least significant) is not set
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75/jump-if-!zero loop/disp8
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b0/copy-to-al 0xd1/imm8
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e6/write-al-into-port 0x64/imm8
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}
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{
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e4/read-port-into-al 0x64/imm8
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a8/test-bits-in-al 0x02/imm8 # set zf if bit 1 (second-least significant) is not set
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75/jump-if-!zero loop/disp8
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b0/copy-to-al 0xdf/imm8
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e6/write-al-into-port 0x64/imm8
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}
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# load remaining sectors from first two tracks of disk into addresses [0x7e00, 0x17800)
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b4/copy-to-ah 2/imm8/read-drive
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# dl comes conveniently initialized at boot time with the index of the device being booted
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b5/copy-to-ch 0/imm8/cylinder
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b6/copy-to-dh 0/imm8/head # <====
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b1/copy-to-cl 2/imm8/sector # 1-based
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b0/copy-to-al 0x7d/imm8/num-sectors # 2*63 - 1 = 125
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# address to write sectors to = es:bx = 0x7e00, contiguous with boot segment
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bb/copy-to-bx 0/imm16
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8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
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bb/copy-to-bx 0x7e00/imm16 # <====
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cd/syscall 0x13/imm8/bios-disk-services
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0f 82/jump-if-carry disk_error/disp16
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# load two more tracks of disk into addresses [0x17800, 0x27400)
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b4/copy-to-ah 2/imm8/read-drive
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# dl comes conveniently initialized at boot time with the index of the device being booted
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b5/copy-to-ch 0/imm8/cylinder
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b6/copy-to-dh 2/imm8/head # <====
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b1/copy-to-cl 1/imm8/sector # 1-based
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b0/copy-to-al 0x7e/imm8/num-sectors # 2*63 = 126
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# address to write sectors to = es:bx = 0x17800, contiguous with boot segment
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bb/copy-to-bx 0x1780/imm16 # <====
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8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
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bb/copy-to-bx 0/imm16
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cd/syscall 0x13/imm8/bios-disk-services
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0f 82/jump-if-carry disk_error/disp16
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# load two more tracks of disk into addresses [0x27400, 0x37000)
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b4/copy-to-ah 2/imm8/read-drive
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# dl comes conveniently initialized at boot time with the index of the device being booted
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b5/copy-to-ch 0/imm8/cylinder
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b6/copy-to-dh 4/imm8/head # <====
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b1/copy-to-cl 1/imm8/sector # 1-based
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b0/copy-to-al 0x7e/imm8/num-sectors # 2*63 = 126
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# address to write sectors to = es:bx = 0x27400, contiguous with boot segment
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bb/copy-to-bx 0x2740/imm16 # <====
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8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
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bb/copy-to-bx 0/imm16
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cd/syscall 0x13/imm8/bios-disk-services
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0f 82/jump-if-carry disk_error/disp16
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# load two more tracks of disk into addresses [0x37000, 0x46c00)
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b4/copy-to-ah 2/imm8/read-drive
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# dl comes conveniently initialized at boot time with the index of the device being booted
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b5/copy-to-ch 0/imm8/cylinder
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b6/copy-to-dh 6/imm8/head # <====
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b1/copy-to-cl 1/imm8/sector # 1-based
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b0/copy-to-al 0x7e/imm8/num-sectors # 2*63 = 126
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# address to write sectors to = es:bx = 0x37000, contiguous with boot segment
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bb/copy-to-bx 0x3700/imm16 # <====
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8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
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bb/copy-to-bx 0/imm16
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cd/syscall 0x13/imm8/bios-disk-services
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0f 82/jump-if-carry disk_error/disp16
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# load two more tracks of disk into addresses [0x46c00, 0x56800)
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b4/copy-to-ah 2/imm8/read-drive
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# dl comes conveniently initialized at boot time with the index of the device being booted
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b5/copy-to-ch 0/imm8/cylinder
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b6/copy-to-dh 8/imm8/head # <====
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b1/copy-to-cl 1/imm8/sector # 1-based
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b0/copy-to-al 0x7e/imm8/num-sectors # 2*63 = 126
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# address to write sectors to = es:bx = 0x46c00, contiguous with boot segment
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bb/copy-to-bx 0x46c0/imm16 # <====
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8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
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bb/copy-to-bx 0/imm16
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cd/syscall 0x13/imm8/bios-disk-services
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0f 82/jump-if-carry disk_error/disp16
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# load two more tracks of disk into addresses [0x56800, 0x66400)
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b4/copy-to-ah 2/imm8/read-drive
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# dl comes conveniently initialized at boot time with the index of the device being booted
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b5/copy-to-ch 0/imm8/cylinder
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b6/copy-to-dh 0xa/imm8/head # <====
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b1/copy-to-cl 1/imm8/sector # 1-based
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b0/copy-to-al 0x7e/imm8/num-sectors # 2*63 = 126
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# address to write sectors to = es:bx = 0x56800, contiguous with boot segment
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bb/copy-to-bx 0x5680/imm16 # <====
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8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
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bb/copy-to-bx 0/imm16
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cd/syscall 0x13/imm8/bios-disk-services
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0f 82/jump-if-carry disk_error/disp16
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# reset es
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bb/copy-to-bx 0/imm16
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8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
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# adjust video mode
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b4/copy-to-ah 0x4f/imm8 # VBE commands
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b0/copy-to-al 2/imm8 # set video mode
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bb/copy-to-bx 0x4105/imm16 # 0x0105 | 0x4000
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# 0x0105 = graphics mode 1024x768x256
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# (alternative candidate: 0x0101 for 640x480x256)
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# 0x4000 bit = configure linear frame buffer in Bochs emulator; hopefully this doesn't hurt anything when running natively
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cd/syscall 0x10/imm8/bios-video-services
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# load information for the (hopefully) current video mode
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# mostly just for the address to the linear frame buffer
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b4/copy-to-ah 0x4f/imm8 # VBE commands
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b0/copy-to-al 1/imm8 # get video mode info
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b9/copy-to-cx 0x0105/imm16 # mode we requested
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bf/copy-to-di Video-mode-info/imm16
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cd/syscall 0x10/imm8/bios-video-services
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## switch to 32-bit mode
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# load global descriptor table
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# We can't refer to the label directly because SubX doesn't do the right
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# thing for lgdt, so rather than make errors worse in most places we instead
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# pin gdt_descriptor below.
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0f 01 2/subop/lgdt 0/mod/indirect 6/rm32/use-disp16 0x7de0/disp16/gdt_descriptor
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# enable paging
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0f 20/<-cr 3/mod/direct 0/rm32/eax 0/r32/cr0
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66 83 1/subop/or 3/mod/direct 0/rm32/eax 1/imm8 # eax <- or 0x1
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0f 22/->cr 3/mod/direct 0/rm32/eax 0/r32/cr0
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# far jump to initialize_32bit_mode that sets cs to offset 8 in the gdt in the process
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# We can't refer to the label directly because SubX doesn't have syntax for
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# segment selectors. So we instead pin initialize_32bit_mode below.
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ea/jump-far-absolute 0x00087e00/disp32 # address 0x7e00 in offset 8 of the gdt
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disk_error:
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# print 'D' to top-left of screen to indicate disk error
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# *0xb8000 <- 0x0f44
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bb/copy-to-bx 0xb800/imm16
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8e/->seg 3/mod/direct 3/rm32/bx 3/r32/ds
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b0/copy-to-al 0x44/imm8/D
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b4/copy-to-ah 0x0f/imm8/white-on-black
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bb/copy-to-bx 0/imm16
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89/<- 0/mod/indirect 7/rm32/bx 0/r32/ax # *ds:bx <- ax
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# loop forever
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{
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eb/jump loop/disp8
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}
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## GDT: 3 records of 8 bytes each
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== data 0x7de0
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gdt_descriptor:
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0x17/imm16 # final index of gdt = size of gdt - 1
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gdt_start/imm32/start
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gdt_start:
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# offset 0: gdt_null: mandatory null descriptor
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00 00 00 00 00 00 00 00
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# offset 8: gdt_code
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ff ff # limit[0:16]
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00 00 00 # base[0:24]
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9a # 1/present 00/privilege 1/descriptor type = 1001b
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# 1/code 0/conforming 1/readable 0/accessed = 1010b
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cf # 1/granularity 1/32-bit 0/64-bit-segment 0/AVL = 1100b
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# limit[16:20] = 1111b
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00 # base[24:32]
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# offset 16: gdt_data
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ff ff # limit[0:16]
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00 00 00 # base[0:24]
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92 # 1/present 00/privilege 1/descriptor type = 1001b
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# 0/data 0/conforming 1/readable 0/accessed = 0010b
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cf # same as gdt_code
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00 # base[24:32]
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# gdt_end:
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== boot-sector-marker 0x7dfe
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# final 2 bytes of boot sector
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55 aa
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## sector 2 onwards loaded by load_disk, not automatically on boot
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## 32-bit code from this point
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== code 0x7e00
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initialize_32bit_mode:
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66 b8/copy-to-ax 0x10/imm16 # offset 16 from gdt_start
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8e/->seg 3/mod/direct 0/rm32/ax 3/r32/ds
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8e/->seg 3/mod/direct 0/rm32/ax 2/r32/ss
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8e/->seg 3/mod/direct 0/rm32/ax 0/r32/es
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8e/->seg 3/mod/direct 0/rm32/ax 4/r32/fs
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8e/->seg 3/mod/direct 0/rm32/ax 5/r32/gs
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bc/copy-to-esp 0x02000000/imm32
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## load interrupt handlers
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# We can't refer to the label directly because SubX doesn't do the right
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# thing for lidt, so rather than make errors worse in most places we instead
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# pin idt_descriptor below.
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0f 01 3/subop/lidt 0/mod/indirect 5/rm32/use-disp32 0x7f00/disp32/idt_descriptor
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# enable timer IRQ0
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b0/copy-to-al 0xfe/imm8 # disable mask for IRQ0
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e6/write-al-into-port 0x21/imm8
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fb/enable-interrupts
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{
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eb/jump loop/disp8
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}
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== data 0x7f00
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idt_descriptor:
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ff 03 # final index of idt = size of idt - 1
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idt_start/imm32/start
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# interrupt descriptor table {{{
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# 32 entries of 8 bytes each
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idt_start:
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# entry 0
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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# By default, BIOS maps IRQ0-7 to interrupt vectors 8-15.
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# https://wiki.osdev.org/index.php?title=Interrupts&oldid=25102#Default_PC_Interrupt_Vector_Assignment
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# entry 8: https://wiki.osdev.org/Programmable_Interval_Timer
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timer-interrupt-handler/imm16 # target[0:16]
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8/imm16 # segment selector (gdt_code)
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00 # unused
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8e # 1/p 00/dpl 0 1110/type/32-bit-interrupt-gate
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0/imm16 # target[16:32] -- timer-interrupt-handler must be within address 0x10000
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00
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# idt_end:
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||||
# }}}
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== code
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||||
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timer-interrupt-handler:
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# prologue
|
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fa/disable-interrupts
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60/push-all-registers
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9c/push-flags
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# acknowledge interrupt
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b0/copy-to-al 0x20/imm8
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e6/write-al-into-port 0x20/imm8
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31/xor %eax 0/r32/eax
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# ecx = *Current-color
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8b/-> *Current-color 1/r32/ecx
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# increment *Current-color
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81 0/subop/add *Current-color 0x01010101/imm32
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# eax = *Video-memory + 0x1200 (a few rows down from top, around middle of screen)
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8b/-> *Video-memory-addr 0/r32/eax
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05/add-to-eax 0x1200/imm32
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89/copy *eax 1/r32/ecx
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# eax += 0x400
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05/add-to-eax 0x400/imm32
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89/copy *eax 1/r32/ecx
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# eax += 0x400
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05/add-to-eax 0x400/imm32
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89/copy *eax 1/r32/ecx
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# eax += 0x400
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05/add-to-eax 0x400/imm32
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89/copy *eax 1/r32/ecx
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$timer-interrupt-handler:epilogue:
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# epilogue
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9d/pop-flags
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61/pop-all-registers
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fb/enable-interrupts
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cf/return-from-interrupt
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== data
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Video-mode-info:
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# video mode info {{{
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0/imm16 # attributes
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00 # winA
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00 # winB
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# 04
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0/imm16 # granularity
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0/imm16 # winsize
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# 08
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0/imm16 # segmentA
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0/imm16 # segmentB
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# 0c
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0/imm32 # realFctPtr (who knows)
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# 10
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0/imm16 # pitch
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0/imm16 # Xres
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0/imm16 # Yres
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0/imm16 # Wchar Ychar
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# 18
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00 # planes
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00 # bpp
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00 # banks
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00 # memory_model
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# 1c
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00 # bank_size
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00 # image_pages
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00 # reserved
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# 1f
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0/imm16 # red_mask red_position
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0/imm16 # green_mask green_position
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0/imm16 # blue_mask blue_position
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0/imm16 # rsv_mask rsv_position
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00 # directcolor_attributes
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# 28
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Video-memory-addr:
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0/imm32 # physbase
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||||
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# 2c
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||||
# reserved for video mode info
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||||
00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
||||
# }}}
|
||||
|
||||
Current-color:
|
||||
0/imm32
|
||||
|
||||
# vim:ft=subx
|
||||
Loading…
Reference in New Issue