# Mu - boot.subx

https://github.com/akkartik/mu/blob/main/boot.subx

       1 # Code for the first few disk sectors that all programs in this directory need:
       2 #   - load sectors past the first (using BIOS primitives) since only the first is available by default
       3 #     - if this fails, print 'D' at top-left of screen and halt
       4 #   - initialize a minimal graphics mode
       5 #   - switch to 32-bit mode (giving up access to BIOS primitives)
       6 #   - set up a handler for keyboard events
       7 #   - jump to start of program
       8
       9 # Code in this file needs to be more deliberate about the SubX facilities it
      10 # uses:
      11 #   - sigils only support 32-bit general-purpose registers, so don't work with segment registers or 16-bit or 8-bit registers
      12 #   - metadata like rm32 and r32 can sometimes misleadingly refer to only the bottom 16 bits of the register; pay attention to the register name
      13 #
      14 # While most of Mu is thoroughly tested, this file is not. I don't yet
      15 # understand hardware interfaces well enough to explain to others.
      16
      17 # Memory map of a Mu computer:
      18 #   code: currently 4 tracks loaded from the primary disk to [0x00007c00, 0x00048600)
      19 #   stack: grows down from 0x02000000 to 0x01000000
      20 #   heap: [0x02000000, 0x08000000)
      21 #     see 120allocate.subx; Qemu initializes with 128MB RAM by default
      22 # Consult https://wiki.osdev.org/Memory_Map_(x86) before modifying any of
      23 # this. And don't forget to keep *stack-debug.subx in sync.
      24
      25 == code
      26
      27 ## 16-bit entry point: 0x7c00
      28
      29 # Upon reset, the IBM PC:
      30 #   - loads the first sector (512 bytes)
      31 #     from some bootable image (look for the boot-sector-marker further down this file)
      32 #     to the address range [0x7c00, 0x7e00)
      33 #   - starts executing code at address 0x7c00
      34
      35   fa/disable-interrupts
      36
      37   # initialize segment registers
      38   b8/copy-to-ax 0/imm16
      39   8e/->seg 3/mod/direct 0/rm32/ax 3/r32/ds
      40   8e/->seg 3/mod/direct 0/rm32/ax 0/r32/es
      41   8e/->seg 3/mod/direct 0/rm32/ax 4/r32/fs
      42   8e/->seg 3/mod/direct 0/rm32/ax 5/r32/gs
      43
      44   # Temporarily initialize stack to 0x00070000 in real mode.
      45   # We don't read or write the stack before we get to 32-bit mode, but BIOS
      46   # calls do. We need to move the stack in case BIOS initializes it to some
      47   # low address that we want to write code into.
      48   b8/copy-to-ax 0x7000/imm16
      49   8e/->seg 3/mod/direct 0/rm32/ax 2/r32/ss
      50   bc/copy-to-esp 0/imm16
      51
      52   # undo the A20 hack: https://en.wikipedia.org/wiki/A20_line
      53   # this is from https://github.com/mit-pdos/xv6-public/blob/master/bootasm.S
      54   {
      55     e4/read-port-into-al 0x64/imm8
      56     a8/test-bits-in-al 0x02/imm8  # set zf if bit 1 (second-least significant) is not set
      57     75/jump-if-!zero loop/disp8
      58     b0/copy-to-al 0xd1/imm8
      59     e6/write-al-into-port 0x64/imm8
      60   }
      61   {
      62     e4/read-port-into-al 0x64/imm8
      63     a8/test-bits-in-al 0x02/imm8  # set zf if bit 1 (second-least significant) is not set
      64     75/jump-if-!zero loop/disp8
      65     b0/copy-to-al 0xdf/imm8
      66     e6/write-al-into-port 0x64/imm8
      67   }
      68
      69   # load remaining sectors from first two tracks of disk into addresses [0x7e00, 0x17800)
      70   b4/copy-to-ah 2/imm8/read-drive
      71   # dl comes conveniently initialized at boot time with the index of the device being booted
      72   b5/copy-to-ch 0/imm8/cylinder
      73   b6/copy-to-dh 0/imm8/head
      74   b1/copy-to-cl 2/imm8/sector  # 1-based
      75   b0/copy-to-al 0x7d/imm8/num-sectors  # 2*63 - 1 = 125
      76   # address to write sectors to = es:bx = 0x7e00, contiguous with boot segment
      77   bb/copy-to-bx 0/imm16
      78   8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
      79   bb/copy-to-bx 0x7e00/imm16
      80   cd/syscall 0x13/imm8/bios-disk-services
      81   0f 82/jump-if-carry disk_error/disp16
      82
      83   # load two more tracks of disk into addresses [0x17800, 0x27400)
      84   b4/copy-to-ah 2/imm8/read-drive
      85   # dl comes conveniently initialized at boot time with the index of the device being booted
      86   b5/copy-to-ch 0/imm8/cylinder
      87   b6/copy-to-dh 2/imm8/head
      88   b1/copy-to-cl 1/imm8/sector  # 1-based
      89   b0/copy-to-al 0x7e/imm8/num-sectors  # 2*63 = 126
      90   # address to write sectors to = es:bx = 0x17800, contiguous with boot segment
      91   bb/copy-to-bx 0x1780/imm16
      92   8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
      93   bb/copy-to-bx 0/imm16
      94   cd/syscall 0x13/imm8/bios-disk-services
      95   0f 82/jump-if-carry disk_error/disp16
      96
      97   # load two more tracks of disk into addresses [0x27400, 0x37000)
      98   b4/copy-to-ah 2/imm8/read-drive
      99   # dl comes conveniently initialized at boot time with the index of the device being booted
     100   b5/copy-to-ch 0/imm8/cylinder
     101   b6/copy-to-dh 4/imm8/head
     102   b1/copy-to-cl 1/imm8/sector  # 1-based
     103   b0/copy-to-al 0x7e/imm8/num-sectors  # 2*63 = 126
     104   # address to write sectors to = es:bx = 0x27400, contiguous with boot segment
     105   bb/copy-to-bx 0x2740/imm16
     106   8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
     107   bb/copy-to-bx 0/imm16
     108   cd/syscall 0x13/imm8/bios-disk-services
     109   0f 82/jump-if-carry disk_error/disp16
     110
     111   # load two more tracks of disk into addresses [0x37000, 0x46c00)
     112   b4/copy-to-ah 2/imm8/read-drive
     113   # dl comes conveniently initialized at boot time with the index of the device being booted
     114   b5/copy-to-ch 0/imm8/cylinder
     115   b6/copy-to-dh 6/imm8/head
     116   b1/copy-to-cl 1/imm8/sector  # 1-based
     117   b0/copy-to-al 0x7e/imm8/num-sectors  # 2*63 = 126
     118   # address to write sectors to = es:bx = 0x37000, contiguous with boot segment
     119   bb/copy-to-bx 0x3700/imm16
     120   8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
     121   bb/copy-to-bx 0/imm16
     122   cd/syscall 0x13/imm8/bios-disk-services
     123   0f 82/jump-if-carry disk_error/disp16
     124
     125   # reset es
     126   bb/copy-to-bx 0/imm16
     127   8e/->seg 3/mod/direct 3/rm32/bx 0/r32/es
     128
     129   # adjust video mode
     130   b4/copy-to-ah 0x4f/imm8  # VBE commands
     131   b0/copy-to-al 2/imm8  # set video mode
     132   bb/copy-to-bx 0x4105/imm16  # 0x0105 | 0x4000
     133                               # 0x0105 = graphics mode 1024x768x256
     134                               #  (alternative candidate: 0x0101 for 640x480x256)
     135                               # 0x4000 bit = configure linear frame buffer in Bochs emulator; hopefully this doesn't hurt anything when running natively
     136   cd/syscall 0x10/imm8/bios-video-services
     137
     138   # load information for the (hopefully) current video mode
     139   # mostly just for the address to the linear frame buffer
     140   b4/copy-to-ah 0x4f/imm8  # VBE commands
     141   b0/copy-to-al 1/imm8  # get video mode info
     142   b9/copy-to-cx 0x0105/imm16  # mode we requested
     143   bf/copy-to-di Video-mode-info/imm16
     144   cd/syscall 0x10/imm8/bios-video-services
     145
     146   ## switch to 32-bit mode
     147   # load global descriptor table
     148   # We can't refer to the label directly because SubX doesn't do the right
     149   # thing for lgdt, so rather than make errors worse in most places we instead
     150   # pin gdt_descriptor below.
     151   0f 01 2/subop/lgdt 0/mod/indirect 6/rm32/use-disp16 0x7ce0/disp16/gdt_descriptor
     152   # enable paging
     153   0f 20/<-cr 3/mod/direct 0/rm32/eax 0/r32/cr0
     154   66 83 1/subop/or 3/mod/direct 0/rm32/eax 1/imm8  # eax <- or 0x1
     155   0f 22/->cr 3/mod/direct 0/rm32/eax 0/r32/cr0
     156   # far jump to initialize_32bit_mode that sets cs to offset 8 in the gdt in the process
     157   # We can't refer to the label directly because SubX doesn't have syntax for
     158   # segment selectors. So we instead pin initialize_32bit_mode below.
     159   ea/jump-far-absolute 0x00087d00/disp32  # address 0x7d00 in offset 8 of the gdt
     160
     161 disk_error:
     162   # print 'D' to top-left of screen to indicate disk error
     163   # *0xb8000 <- 0x0f44
     164   bb/copy-to-bx 0xb800/imm16
     165   8e/->seg 3/mod/direct 3/rm32/bx 3/r32/ds
     166   b0/copy-to-al 0x44/imm8/D
     167   b4/copy-to-ah 0x0f/imm8/white-on-black
     168   bb/copy-to-bx 0/imm16
     169   89/<- 0/mod/indirect 7/rm32/bx 0/r32/ax  # *ds:bx <- ax
     170   # loop forever
     171   {
     172     eb/jump loop/disp8
     173   }
     174
     175 ## GDT: 3 records of 8 bytes each
     176 == data 0x7ce0
     177 gdt_descriptor:
     178   0x17/imm16  # final index of gdt = size of gdt - 1
     179   gdt_start/imm32/start
     180
     181 gdt_start:
     182 # offset 0: gdt_null:  mandatory null descriptor
     183   00 00 00 00 00 00 00 00
     184 # offset 8: gdt_code
     185   ff ff  # limit[0:16]
     186   00 00 00  # base[0:24]
     187   9a  # 1/present 00/privilege 1/descriptor type = 1001b
     188       # 1/code 0/conforming 1/readable 0/accessed = 1010b
     189   cf  # 1/granularity 1/32-bit 0/64-bit-segment 0/AVL = 1100b
     190       # limit[16:20] = 1111b
     191   00  # base[24:32]
     192 # offset 16: gdt_data
     193   ff ff  # limit[0:16]
     194   00 00 00  # base[0:24]
     195   92  # 1/present 00/privilege 1/descriptor type = 1001b
     196       # 0/data 0/conforming 1/readable 0/accessed = 0010b
     197   cf  # same as gdt_code
     198   00  # base[24:32]
     199 # gdt_end:
     200
     201 ## 32-bit code from this point
     202
     203 == code 0x7d00
     204 initialize_32bit_mode:
     205   66 b8/copy-to-ax 0x10/imm16  # offset 16 from gdt_start
     206   8e/->seg 3/mod/direct 0/rm32/ax 3/r32/ds
     207   8e/->seg 3/mod/direct 0/rm32/ax 2/r32/ss
     208   8e/->seg 3/mod/direct 0/rm32/ax 0/r32/es
     209   8e/->seg 3/mod/direct 0/rm32/ax 4/r32/fs
     210   8e/->seg 3/mod/direct 0/rm32/ax 5/r32/gs
     211
     212   bc/copy-to-esp 0x02000000/imm32
     213
     214   ## load interrupt handlers
     215   # We can't refer to the label directly because SubX doesn't do the right
     216   # thing for lidt, so rather than make errors worse in most places we instead
     217   # pin idt_descriptor below.
     218   0f 01 3/subop/lidt 0/mod/indirect 5/rm32/use-disp32 0x7e00/disp32/idt_descriptor
     219
     220   # For now, not bothering reprogramming the IRQ to not conflict with software
     221   # exceptions.
     222   #   https://wiki.osdev.org/index.php?title=8259_PIC&oldid=24650#Protected_Mode
     223   #
     224   # Interrupt 1 (keyboard) conflicts with debugger faults. We don't use a
     225   # debugger.
     226   # Reference:
     227   #   https://wiki.osdev.org/Exceptions
     228
     229   # enable timer IRQ0 and keyboard IRQ1
     230   b0/copy-to-al 0xfc/imm8  # disable mask for IRQ0 and IRQ1
     231   e6/write-al-into-port 0x21/imm8
     232
     233   fb/enable-interrupts
     234
     235   (initialize-mouse)
     236
     237   ## enable floating point
     238   db/floating-point-coprocessor e3/initialize
     239   # eax <- cr4
     240   0f 20/<-cr 3/mod/direct 0/rm32/eax 4/r32/cr4
     241   # eax <- or bit 9
     242   0f ba/bit-test 5/subop/bit-test-and-set 3/mod/direct 0/rm32/eax 9/imm8
     243   # cr4 <- eax
     244   0f 22/->cr 3/mod/direct 0/rm32/eax 4/r32/cr4
     245
     246   e9/jump Entry/disp32
     247
     248 == boot-sector-marker 0x7dfe
     249 # final 2 bytes of boot sector
     250 55 aa
     251
     252 ## sector 2 onwards loaded by load_disk, not automatically on boot
     253
     254 == data 0x7e00
     255 idt_descriptor:
     256   ff 03  # final index of idt = size of idt - 1
     257   idt_start/imm32/start
     258
     259 +-- 55 lines: # interrupt descriptor table ----------------------------------------------------------------------------------------------------------------------------------------------
     314
     315 == code
     316
     317 null-interrupt-handler:
     318   # prologue
     319   # Don't disable interrupts; the timer has the highest priority anyway,
     320   # and this interrupt triggers extremely frequently.
     321   fa/disable-interrupts
     322   60/push-all-registers
     323   9c/push-flags
     324   # acknowledge interrupt
     325   b0/copy-to-al 0x20/imm8
     326   e6/write-al-into-port 0x20/imm8
     327   31/xor %eax 0/r32/eax
     328 $null-interrupt-handler:epilogue:
     329   # epilogue
     330   9d/pop-flags
     331   61/pop-all-registers
     332   fb/enable-interrupts
     333   cf/return-from-interrupt
     334
     335 timer-interrupt-handler:
     336   # prologue
     337   # Don't disable interrupts; the timer has the highest priority anyway,
     338   # and this interrupt triggers extremely frequently.
     339   fa/disable-interrupts
     340   60/push-all-registers
     341   9c/push-flags
     342   # acknowledge interrupt
     343   b0/copy-to-al 0x20/imm8
     344   e6/write-al-into-port 0x20/imm8
     345   31/xor %eax 0/r32/eax
     346 $timer-interrupt-handler:epilogue:
     347   # epilogue
     348   9d/pop-flags
     349   61/pop-all-registers
     350   fb/enable-interrupts
     351   cf/return-from-interrupt
     352
     353 keyboard-interrupt-handler:
     354   # prologue
     355   fa/disable-interrupts
     356   60/push-all-registers
     357   9c/push-flags
     358   # acknowledge interrupt
     359   b0/copy-to-al 0x20/imm8
     360   e6/write-al-into-port 0x20/imm8
     361   31/xor %eax 0/r32/eax
     362   # check output buffer of 8042 keyboard controller (https://web.archive.org/web/20040604041507/http://panda.cs.ndsu.nodak.edu/~achapwes/PICmicro/keyboard/atkeyboard.html)
     363   e4/read-port-into-al 0x64/imm8
     364   a8/test-bits-in-al 0x01/imm8  # set zf if bit 0 (least significant) is not set
     365   0f 84/jump-if-not-set $keyboard-interrupt-handler:epilogue/disp32
     366   # - if keyboard buffer is full, return
     367   # var dest-addr/ecx: (addr byte) = (keyboard-buffer + *keyboard-buffer:write)
     368   31/xor %ecx 1/r32/ecx
     369   8a/byte-> *Keyboard-buffer:write 1/r32/cl
     370   81 0/subop/add %ecx Keyboard-buffer:data/imm32
     371   # al = *dest-addr
     372   8a/byte-> *ecx 0/r32/al
     373   # if (al != 0) return
     374   3c/compare-al-and 0/imm8
     375   0f 85/jump-if-!= $keyboard-interrupt-handler:epilogue/disp32
     376   # - read keycode
     377   e4/read-port-into-al 0x60/imm8
     378   # - key released
     379   # if (al == 0xaa) shift = false  # left shift is being lifted
     380   {
     381     3c/compare-al-and 0xaa/imm8
     382     75/jump-if-!= break/disp8
     383     # *shift = 0
     384     c7 0/subop/copy *Keyboard-shift-pressed? 0/imm32
     385   }
     386   # if (al == 0xb6) shift = false  # right shift is being lifted
     387   {
     388     3c/compare-al-and 0xb6/imm8
     389     75/jump-if-!= break/disp8
     390     # *shift = 0
     391     c7 0/subop/copy *Keyboard-shift-pressed? 0/imm32
     392   }
     393   # if (al == 0x9d) ctrl = false  # ctrl is being lifted
     394   {
     395     3c/compare-al-and 0x9d/imm8
     396     75/jump-if-!= break/disp8
     397     # *ctrl = 0
     398     c7 0/subop/copy *Keyboard-ctrl-pressed? 0/imm32
     399   }
     400   # if (al & 0x80) a key is being lifted; return
     401   50/push-eax
     402   24/and-al-with 0x80/imm8
     403   3c/compare-al-and 0/imm8
     404   58/pop-to-eax
     405   75/jump-if-!= $keyboard-interrupt-handler:epilogue/disp8
     406   # - key pressed
     407   # if (al == 0x2a) shift = true, return  # left shift pressed
     408   {
     409     3c/compare-al-and 0x2a/imm8
     410     75/jump-if-!= break/disp8
     411     # *shift = 1
     412     c7 0/subop/copy *Keyboard-shift-pressed? 1/imm32
     413     # return
     414     eb/jump $keyboard-interrupt-handler:epilogue/disp8
     415   }
     416   # if (al == 0x36) shift = true, return  # right shift pressed
     417   {
     418     3c/compare-al-and 0x36/imm8
     419     75/jump-if-!= break/disp8
     420     # *shift = 1
     421     c7 0/subop/copy *Keyboard-shift-pressed? 1/imm32
     422     # return
     423     eb/jump $keyboard-interrupt-handler:epilogue/disp8
     424   }
     425   # if (al == 0x1d) ctrl = true, return
     426   {
     427     3c/compare-al-and 0x1d/imm8
     428     75/jump-if-!= break/disp8
     429     # *ctrl = 1
     430     c7 0/subop/copy *Keyboard-ctrl-pressed? 1/imm32
     431     # return
     432     eb/jump $keyboard-interrupt-handler:epilogue/disp8
     433   }
     434   # - convert key to character
     435   # if (shift) use keyboard shift map
     436   {
     437     81 7/subop/compare *Keyboard-shift-pressed? 0/imm32
     438     74/jump-if-= break/disp8
     439     # sigils don't currently support labels inside *(eax+label)
     440     05/add-to-eax Keyboard-shift-map/imm32
     441     8a/byte-> *eax 0/r32/al
     442     eb/jump $keyboard-interrupt-handler:select-map-done/disp8
     443   }
     444   # if (ctrl) al = *(ctrl map + al)
     445   {
     446     81 7/subop/compare *Keyboard-ctrl-pressed? 0/imm32
     447     74/jump-if-= break/disp8
     448     05/add-to-eax Keyboard-ctrl-map/imm32
     449     8a/byte-> *eax 0/r32/al
     450     eb/jump $keyboard-interrupt-handler:select-map-done/disp8
     451   }
     452   # otherwise al = *(normal map + al)
     453   05/add-to-eax Keyboard-normal-map/imm32
     454   8a/byte-> *eax 0/r32/al
     455 $keyboard-interrupt-handler:select-map-done:
     456   # - if there's no character mapping, return
     457   {
     458     3c/compare-al-and 0/imm8
     459     74/jump-if-= break/disp8
     460     # - store al in keyboard buffer
     461     88/<- *ecx 0/r32/al
     462     # increment index
     463     fe/increment-byte *Keyboard-buffer:write
     464     # clear top nibble of index (keyboard buffer is circular)
     465     80 4/subop/and-byte *Keyboard-buffer:write 0x0f/imm8
     466   }
     467 $keyboard-interrupt-handler:epilogue:
     468   # epilogue
     469   9d/pop-flags
     470   61/pop-all-registers
     471   fb/enable-interrupts
     472   cf/return-from-interrupt
     473
     474 == data
     475 Keyboard-shift-pressed?:  # boolean
     476   0/imm32
     477
     478 Keyboard-ctrl-pressed?:  # boolean
     479   0/imm32
     480
     481 # var keyboard circular buffer
     482 Keyboard-buffer:write:  # nibble
     483   0/imm32
     484 Keyboard-buffer:read:  # nibble
     485   0/imm32
     486 Keyboard-buffer:data:  # byte[16]
     487   00 00 00 00
     488   00 00 00 00
     489   00 00 00 00
     490   00 00 00 00
     491
     492 +-- 95 lines: # Keyboard maps for translating keys to ASCII -----------------------------------------------------------------------------------------------------------------------------
     587
     588 Video-mode-info:
     589 +-- 53 lines: # video mode info ---------------------------------------------------------------------------------------------------------------------------------------------------------
     642
     643 Font:
     644 +--236 lines: # Bitmaps for some ASCII characters (soon Unicode) ------------------------------------------------------------------------------------------------------------------------
     880
     881 ## Controlling IDE (ATA) hard disks
     882 # Uses 28-bit PIO mode.
     883 # Inspired by https://colorforth.github.io/ide.html
     884 #
     885 # Resources:
     886 #   https://wiki.osdev.org/ATA_PIO_Mode
     887 #   https://forum.osdev.org/viewtopic.php?f=1&p=167798
     888 #   read-sector, according to https://www.scs.stanford.edu/11wi-cs140/pintos/specs/ata-3-std.pdf
     889
     890 == data
     891
     892 # We'll be gaining access just to the secondary drive on the primary bus for
     893 # now. It will have the designated 'data' disk so we don't mess with the code
     894 # disk.
     895 #
     896 # The type definition for this variable is in safe Mu (rather than unsafe
     897 # SubX) code.
     898 # All ports are 8-bit except data-port, which is 16-bit.
     899 Primary-bus-secondary-drive:
     900   # command-port: int (write)
     901   0x1f7/imm32
     902   # status-port: int (read)
     903   0x1f7/imm32
     904   # alternative-status-port: int (read)
     905   0x3f6/imm32
     906   # error-port: int (read)
     907   0x1f1/imm32
     908   # drive-and-head-port: int
     909   0x1f6/imm32
     910   # sector-count-port: int
     911   0x1f2/imm32
     912   # lba-low-port: int
     913   0x1f3/imm32
     914   # lba-mid-port: int
     915   0x1f4/imm32
     916   # lba-high-port: int
     917   0x1f5/imm32
     918   # data-port: int
     919   0x1f0/imm32
     920   # drive-code: byte                # only drive-specific field
     921   0xf0/imm32  # LBA mode also enabled
     922
     923 == code
     924
     925 load-sectors:  # disk: (addr disk), lba: int, n: int, out: (addr stream byte)
     926   # . prologue
     927   55/push-ebp
     928   89/<- %ebp 4/r32/esp
     929   # . save registers
     930   50/push-eax
     931   51/push-ecx
     932   52/push-edx
     933   # check for drive
     934   (drive-exists? *(ebp+8))  # => eax
     935   3d/compare-eax-and 0/imm32/false
     936   0f 84/jump-if-= $load-sectors:end/disp32
     937   # kick off read
     938   (ata-drive-select *(ebp+8) *(ebp+0xc))
     939   (clear-ata-error *(ebp+8))
     940   (ata-sector-count *(ebp+8) *(ebp+0x10))
     941   (ata-lba *(ebp+8) *(ebp+0xc))
     942   (ata-command *(ebp+8) 0x20)  # read sectors with retries
     943   # for each sector
     944   {
     945     # poll for results
     946 #?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "waiting for sector.." 7 0)
     947     (while-ata-busy *(ebp+8))
     948     (until-ata-data-available *(ebp+8))
     949 #?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "reading\n" 7 0)
     950     # var data-port/edx = disk->data-port
     951     8b/-> *(ebp+8) 0/r32/eax
     952     8b/-> *(eax+0x24) 2/r32/edx
     953     # emit results
     954     31/xor %eax 0/r32/eax
     955     b9/copy-to-ecx 0x200/imm32  # 512 bytes per sector
     956     {
     957       81 7/subop/compare %ecx 0/imm32
     958       74/jump-if-= break/disp8
     959       66 ed/read-port-dx-into-ax
     960       # write 2 bytes to stream one at a time
     961       (append-byte *(ebp+0x14) %eax)
     962       49/decrement-ecx
     963       c1/shift 5/subop/right-padding-zeroes %eax 8/imm8
     964       (append-byte *(ebp+0x14) %eax)
     965       49/decrement-ecx
     966       eb/jump loop/disp8
     967     }
     968     # next sector
     969     ff 1/subop/decrement *(ebp+0x10)
     970 #?     (draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0 *(ebp+0x10) 0xc 0)
     971     81 7/subop/compare *(ebp+0x10) 0/imm32
     972     7e/jump-if-<= break/disp8
     973     (wait-400ns *(ebp+8))
     974 #?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "next sector\n" 7 0)
     975     e9/jump loop/disp32
     976   }
     977 $load-sectors:end:
     978   # . restore registers
     979   5a/pop-to-edx
     980   59/pop-to-ecx
     981   58/pop-to-eax
     982   # . epilogue
     983   89/<- %esp 5/r32/ebp
     984   5d/pop-to-ebp
     985   c3/return
     986
     987 store-sectors:  # disk: (addr disk), lba: int, n: int, in: (addr stream byte)
     988   # . prologue
     989   55/push-ebp
     990   89/<- %ebp 4/r32/esp
     991   # . save registers
     992   50/push-eax
     993   51/push-ecx
     994   52/push-edx
     995   53/push-ebx
     996   # check for drive
     997   (drive-exists? *(ebp+8))  # => eax
     998   3d/compare-eax-and 0/imm32/false
     999   0f 84/jump-if-= $store-sectors:end/disp32
    1000   # kick off write
    1001   (ata-drive-select *(ebp+8) *(ebp+0xc))
    1002   (clear-ata-error *(ebp+8))
    1003   (ata-sector-count *(ebp+8) *(ebp+0x10))
    1004   (ata-lba *(ebp+8) *(ebp+0xc))
    1005   (ata-command *(ebp+8) 0x30)  # write sectors with retries
    1006   # for each sector
    1007 #?   (set-cursor-position 0 0 0)
    1008 #?   (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "0" 7 0)
    1009   {
    1010     # wait
    1011     (while-ata-busy *(ebp+8))
    1012     (until-ata-ready-for-data *(ebp+8))
    1013     # var data-port/edx = disk->data-port
    1014     8b/-> *(ebp+8) 0/r32/eax
    1015     8b/-> *(eax+0x24) 2/r32/edx
    1016     # send data
    1017     b9/copy-to-ecx 0x200/imm32  # 512 bytes per sector
    1018     # . var first-byte/ebx: byte
    1019     # . when it's more than 0xff, we're at an even-numbered byte
    1020     bb/copy-to-ebx 0xffff/imm32
    1021 #?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "D" 7 0)
    1022 $store-sectors:store-sector:
    1023     {
    1024       81 7/subop/compare %ecx 0/imm32
    1025       74/jump-if-= break/disp8
    1026       # this loop is slow, but the ATA spec also requires a small delay
    1027       (stream-empty? *(ebp+0x14))  # => eax
    1028       3d/compare-eax-and 0/imm32/false
    1029       75/jump-if-!= break/disp8
    1030       # read byte from stream
    1031       (read-byte *(ebp+0x14))  # => eax
    1032       # if we're at an odd-numbered byte, save it to first-byte
    1033       81 7/subop/compare %ebx 0xff/imm32
    1034       {
    1035         7e/jump-if-<= break/disp8
    1036         89/<- %ebx 0/r32/eax
    1037         eb/jump $store-sectors:store-sector/disp8
    1038       }
    1039       # otherwise OR it with first-byte and write it out
    1040       c1/shift 4/subop/left %eax 8/imm8
    1041       09/or %eax 3/r32/ebx
    1042       66 ef/write-ax-into-port-dx
    1043       49/decrement-ecx
    1044       49/decrement-ecx
    1045       # reset first-byte
    1046       bb/copy-to-ebx 0xffff/imm32
    1047       eb/jump loop/disp8
    1048     }
    1049     # write out final first-byte if necessary
    1050 #?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "I" 7 0)
    1051     81 7/subop/compare %ebx 0xff/imm32
    1052     {
    1053       7f/jump-if-> break/disp8
    1054       89/<- %eax 3/r32/ebx
    1055       66 ef/write-ax-into-port-dx
    1056       49/decrement-ecx
    1057       49/decrement-ecx
    1058     }
    1059     # pad zeroes
    1060 #?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "P" 7 0)
    1061     31/xor %eax 0/r32/eax
    1062     {
    1063       81 7/subop/compare %ecx 0/imm32
    1064       74/jump-if-= break/disp8
    1065       66 ef/write-ax-into-port-dx
    1066       49/decrement-ecx
    1067       49/decrement-ecx
    1068       eb/jump loop/disp8
    1069     }
    1070     # next sector
    1071 #?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "N" 7 0)
    1072     ff 1/subop/decrement *(ebp+0x10)
    1073     81 7/subop/compare *(ebp+0x10) 0/imm32
    1074     7e/jump-if-<= break/disp8
    1075 #?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "W" 7 0)
    1076     (wait-400ns *(ebp+8))
    1077 #?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "L" 7 0)
    1078     e9/jump loop/disp32
    1079   }
    1080 #?   (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "F" 7 0)
    1081   (flush-ata-cache *(ebp+8))
    1082 #?   (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "Y" 7 0)
    1083 $store-sectors:end:
    1084   # . restore registers
    1085   5b/pop-to-ebx
    1086   5a/pop-to-edx
    1087   59/pop-to-ecx
    1088   58/pop-to-eax
    1089   # . epilogue
    1090   89/<- %esp 5/r32/ebp
    1091   5d/pop-to-ebp
    1092   c3/return
    1093
    1094 +--289 lines: # disk helpers ------------------------------------------------------------------------------------------------------------------------------------------------------------
    1383
    1384 ## Controlling a PS/2 mouse
    1385 # Uses no IRQs, just polling.
    1386 # Thanks Dave Long: https://github.com/jtauber/cleese/blob/master/necco/kernel/bochs/py8042.py
    1387 #
    1388 # Resources:
    1389 #   https://wiki.osdev.org/Mouse_Input
    1390
    1391 # results x/eax, y/ecx range from -256 to +255
    1392 # See https://wiki.osdev.org/index.php?title=Mouse_Input&oldid=25663#Format_of_First_3_Packet_Bytes
    1393 read-mouse-event:  # -> _/eax: int, _/ecx: int
    1394   # . prologue
    1395   55/push-ebp
    1396   89/<- %ebp 4/r32/esp
    1397   # . save registers
    1398   52/push-edx
    1399   53/push-ebx
    1400   # if no event, return 0, 0
    1401   b8/copy-to-eax 0/imm32
    1402   b9/copy-to-ecx 0/imm32
    1403   (any-mouse-event?)  # => eax
    1404   3d/compare-eax-and 0/imm32/false
    1405   74/jump-if-= $read-mouse-event:end/disp8
    1406   # var f1/edx: byte = inb(0x60)
    1407   31/xor %eax 0/r32/eax
    1408   e4/read-port-into-al 0x60/imm8
    1409   89/<- %edx 0/r32/eax
    1410   (wait-for-mouse-event)
    1411   # var dx/ebx: byte = inb(0x60)
    1412   31/xor %eax 0/r32/eax
    1413   e4/read-port-into-al 0x60/imm8
    1414   89/<- %ebx 0/r32/eax
    1415   (wait-for-mouse-event)
    1416   # var dy/ecx: byte = inb(0x60)
    1417   31/xor %eax 0/r32/eax
    1418   e4/read-port-into-al 0x60/imm8
    1419   89/<- %ecx 0/r32/eax
    1420   # eax = dx
    1421   89/<- %eax 3/r32/ebx
    1422   # if (f1 & 0x10) dx = -dx
    1423   {
    1424     f6 0/subop/test-bits %dl 0x10/imm8
    1425     74/jump-if-zero break/disp8
    1426     0d/or-eax-with 0xffffff00/imm32
    1427   }
    1428   # if (f1 & 0x20) dy = -dy
    1429   {
    1430     f6 0/subop/test-bits %dl 0x20/imm8
    1431     74/jump-if-zero break/disp8
    1432     81 1/subop/or %ecx 0xffffff00/imm32
    1433   }
    1434 $read-mouse-event:end:
    1435   # . restore registers
    1436   5b/pop-to-ebx
    1437   5a/pop-to-edx
    1438   # . epilogue
    1439   89/<- %esp 5/r32/ebp
    1440   5d/pop-to-ebp
    1441   c3/return
    1442
    1443 +--147 lines: # mouse helpers -----------------------------------------------------------------------------------------------------------------------------------------------------------
    1590
    1591 # vim:ft=subx