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Updated the README and added the code from the John Burger tutorial o…
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| ; | ||
| ; BIOS/A20.inc | ||
| ; | ||
|
|
||
| ; These are the definitions for the BIOS A20 controller | ||
| BIOS.A20.Int EQU 15h | ||
| BIOS.A20.Fn EQU 24h | ||
| BIOS.A20.Enable EQU 01h | ||
| BIOS.A20.Disable EQU 00h |
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| ; | ||
| ; BIOS/BIOS.inc | ||
| ; | ||
|
|
||
| ; The original IBM PC BIOS, and various successors, have all embodied relatively | ||
| ; arbitrary design decisions that have become industry standards. Of course, not | ||
| ; every BIOS uses the same definitions, and others had bugs which were fixed in | ||
| ; later versions, but those arbitrary decisions need to be either utilised or | ||
| ; accommodated by any system wanting to work on the PC. | ||
|
|
||
| BIOS.RAMTop.Int EQU 12h | ||
|
|
||
| ;------------------------------------------------------------------------------- | ||
| %include "BIOS/A20.inc" ; Definitions for A20 Gate controller | ||
| ;------------------------------------------------------------------------------- | ||
| %include "BIOS/RAMMap.inc" ; Definitions for RAMMap information | ||
| ;------------------------------------------------------------------------------- | ||
| %include "BIOS/Key.inc" ; Definitions for Keyboard | ||
| ;------------------------------------------------------------------------------- | ||
| %include "BIOS/VGA.inc" ; Definitions for VGA video | ||
| ;------------------------------------------------------------------------------- | ||
| %include "BIOS/Disk.inc" ; Definitions for Disk controller | ||
| ;------------------------------------------------------------------------------- | ||
| %include "BIOS/MBR.inc" ; Definitions for Master Boot Record | ||
| ;------------------------------------------------------------------------------- | ||
| %include "BIOS/MemMap.inc" ; Definitions for boot-time memory map |
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| ; | ||
| ; BIOS/Disk.inc | ||
| ; | ||
|
|
||
| ; These are the definitions for the BIOS Disk controller | ||
|
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||
| BIOS.Disk.Sector.Size EQU 512 | ||
|
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||
| BIOS.Disk.Int EQU 13h | ||
| BIOS.Disk.Fn.Reset EQU 00h | ||
| BIOS.Disk.Fn.Read EQU 02h |
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| ; | ||
| ; BIOS/Key.inc | ||
| ; | ||
|
|
||
| ; These are the definitions for the BIOS keyboard controller | ||
|
|
||
| BIOS.Key.Int EQU 16h | ||
|
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||
| BIOS.Key.SetRate.Fn EQU 03h | ||
| BIOS.Key.SetRate.Default EQU 00h ; Set back to default | ||
| BIOS.Key.SetRate.Increase EQU 01h | ||
| BIOS.Key.SetRate.Decrease EQU 02h ; Slow down by half | ||
| BIOS.Key.SetRate.Off EQU 04h ; Turn off | ||
| BIOS.Key.SetRate.Set EQU 05h ; Set to below values (BH:BL) | ||
|
|
||
| ; Delay before typematic starts, in milliseconds (in BH) | ||
| BIOS.Key.SetRate.Delay.250 EQU 00h | ||
| BIOS.Key.SetRate.Delay.500 EQU 01h | ||
| BIOS.Key.SetRate.Delay.750 EQU 02h | ||
| BIOS.Key.SetRate.Delay.1000 EQU 03h | ||
|
|
||
| ; Rate at which typematic occurs, in chars per 10 seconds (in BL) | ||
| BIOS.Key.SetRate.Rate.300 EQU 00h | ||
| BIOS.Key.SetRate.Rate.267 EQU 01h | ||
| BIOS.Key.SetRate.Rate.240 EQU 02h | ||
| BIOS.Key.SetRate.Rate.218 EQU 03h | ||
| BIOS.Key.SetRate.Rate.200 EQU 04h | ||
| BIOS.Key.SetRate.Rate.185 EQU 05h | ||
| BIOS.Key.SetRate.Rate.171 EQU 06h | ||
| BIOS.Key.SetRate.Rate.160 EQU 07h | ||
| BIOS.Key.SetRate.Rate.150 EQU 08h | ||
| BIOS.Key.SetRate.Rate.133 EQU 09h | ||
| BIOS.Key.SetRate.Rate.120 EQU 0Ah | ||
| BIOS.Key.SetRate.Rate.109 EQU 0Bh | ||
| BIOS.Key.SetRate.Rate.100 EQU 0Ch | ||
| BIOS.Key.SetRate.Rate.92 EQU 0Dh | ||
| BIOS.Key.SetRate.Rate.86 EQU 0Eh | ||
| BIOS.Key.SetRate.Rate.80 EQU 0Fh | ||
| BIOS.Key.SetRate.Rate.75 EQU 10h | ||
| BIOS.Key.SetRate.Rate.67 EQU 11h | ||
| BIOS.Key.SetRate.Rate.60 EQU 12h | ||
| BIOS.Key.SetRate.Rate.55 EQU 13h | ||
| BIOS.Key.SetRate.Rate.50 EQU 14h | ||
| BIOS.Key.SetRate.Rate.46 EQU 15h | ||
| BIOS.Key.SetRate.Rate.43 EQU 16h | ||
| BIOS.Key.SetRate.Rate.40 EQU 17h | ||
| BIOS.Key.SetRate.Rate.37 EQU 18h | ||
| BIOS.Key.SetRate.Rate.33 EQU 19h | ||
| BIOS.Key.SetRate.Rate.30 EQU 1Ah | ||
| BIOS.Key.SetRate.Rate.27 EQU 1Bh | ||
| BIOS.Key.SetRate.Rate.25 EQU 1Ch | ||
| BIOS.Key.SetRate.Rate.23 EQU 1Dh | ||
| BIOS.Key.SetRate.Rate.21 EQU 1Eh | ||
| BIOS.Key.SetRate.Rate.20 EQU 1Fh |
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| ; | ||
| ; BIOS/MBR.inc | ||
| ; | ||
|
|
||
| ; These are the definitions for the standard BIOS Master Boot Record | ||
|
|
||
| ; If we booted from a hard disk, ES:SI will be pointing to the relevant Partition | ||
| STRUC BIOS.MBR.Entry | ||
| .Active RESB 1 | ||
| .StartHead RESB 1 | ||
| .StartCylSect RESW 1 | ||
| .Type RESB 1 | ||
| .EndHead RESB 1 | ||
| .EndCylSect RESW 1 | ||
| .Start RESD 1 | ||
| .Size RESD 1 | ||
| ENDSTRUC | ||
|
|
||
| ; The two CylSect entries above have the following format. But don't be fooled! | ||
| ; The HIGH bits of the Cylinder are in the LOW byte - it's weirdly reversed! | ||
| BIOS.MBR.Entry.Cyl EQU 1111_1111_1100_0000b | ||
| BIOS.MBR.Entry.Sect EQU 0000_0000_0011_1111b |
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| ; | ||
| ; BIOS/MemMap.inc | ||
| ; | ||
|
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| ; This is the Memory Map of when the BIOS first boots. | ||
|
|
||
| ; You'll notice that the Stack is on top of the Interrupt Vector Table! | ||
| BIOS.Stack.Base EQU 0000h ; BIOS Boot stack | ||
| BIOS.Stack.Size EQU 0400h | ||
|
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||
| BIOS.BDA.Base EQU 0400h ; BIOS Data Area | ||
| BIOS.BDA.Size EQU 0100h | ||
|
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| BIOS.MBR.Base EQU 0600h ; BIOS Master Boot Record load area | ||
| BIOS.MBR.Size EQU 0200h | ||
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| BIOS.Entry EQU 7C00h ; BIOS Boot Entry point | ||
|
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| BIOS.Sig.Value EQU 0AA55h ; BIOS Signature flag | ||
| BIOS.Sig.Pos EQU BIOS.Disk.Sector.Size - 2 |
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| ; | ||
| ; BIOS/RAMMap.inc | ||
| ; | ||
|
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| ; These are the definitions for the BIOS RAM Map information handler | ||
|
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| BIOS.RAMMap.Int EQU 15h | ||
| BIOS.RAMMap.Fn EQU 0000_E820h | ||
| BIOS.RAMMap.Magic EQU "PAMS" ; NASM reverses "SMAP" | ||
|
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||
| ; This is the BIOS RAMMap structure | ||
| STRUC BIOS.RAMMap | ||
| .Base RESQ 1 | ||
| .Length RESQ 1 | ||
| .Type RESD 1 | ||
| .Flags RESD 1 ; Added in later BIOSes | ||
| ENDSTRUC | ||
|
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| BIOS.RAMMap.Flags.DontIgnore EQU 0000_0000_0000_0001b |
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| ; | ||
| ; BIOS/VGA.inc | ||
| ; | ||
|
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| ; These are the definitions for the BIOS video controller | ||
|
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||
| BIOS.VGA.Int EQU 10h | ||
|
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| BIOS.VGA.SetMode.Fn EQU 00h | ||
| BIOS.VGA.SetMode.80x25 EQU 03h | ||
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| BIOS.VGA.ExtMode.Fn EQU 11h | ||
| BIOS.VGA.ExtMode.80x50 EQU 12h | ||
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| BIOS.VGA.Cursor.Fn EQU 01h | ||
| BIOS.VGA.Cursor.None EQU 0010_0000_0000_0000b | ||
| BIOS.VGA.Cursor.Under EQU 06_07h | ||
| BIOS.VGA.Cursor.Block EQU 00_07h |
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| ; | ||
| ; Boot/A20.inc | ||
| ; | ||
|
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||
| ; The 8086 has a 20-bit address bus. If you loaded a segment register with | ||
| ; 0FFFFh and accessed 0FFFFh:0FFFFh, the Segment:Offset addition would wrap | ||
| ; and you'd actually be accessing 0000_FFEFh. The BIOS would "take advantage" | ||
| ; of this quirk and use it to access both top-of-Address BIOS and botttom-of- | ||
| ; Address RAM with the same segment register. | ||
| ; | ||
| ; Of course, then the '286 PC/AT came out with a 24-bit bus - and the wrap no | ||
| ; longer occurred. You could use it to access the (nearly) 64K of High Memory! | ||
| ; But what about all the legacy code? That was now broken. | ||
| ; | ||
| ; To "fix" this, the designers of the PC/AT added a Gate to the A20 line, to | ||
| ; hold A20 on the memory bus at zero regardless of what the CPU wanted. This | ||
| ; emulated the wrap-around "feature", but made the high memory inaccessible. | ||
| ; | ||
| ; So to fix that, they found a spare output that they could program at run-time | ||
| ; to turn the Gate on or off. Where was this spare pin? The keyboard controller, | ||
| ; of course... | ||
| ; | ||
| ; As PCs became more sophisticated, the A20 Gate stayed, but the programming | ||
| ; mechanism to turn it on or off changed - and it wasn't really standardised. | ||
| ; Since this program wants to access high memory, it has to turn off the Gate - | ||
| ; and it uses a number of techniques to attempt this. | ||
| ; | ||
| ; Of course, this means finding out whether A20 is off, both up front and after | ||
| ; each technique. How? Go to a known memory location, get its value, and compare | ||
| ; it with its high-memory "alias". If they're different, then the Gate is off. | ||
| ; If they're the same, then maybe it was a coincidence? Change the original | ||
| ; location, and check the alias again. If they're now different (they were the | ||
| ; same, but now they're different), the Gate must be off. | ||
|
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| A20.Enable EQU (BIOS.A20.Fn << 8) | BIOS.A20.Enable | ||
|
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| ; [0000h:BIOS.Entry + BIOS.Sig.Pos] holds the value BIOS.Sig.Value | ||
| ; [FFFFh:BIOS.Entry + BIOS.Sig.Pos + 10h] is its alias, if the A20 Gate is on. | ||
| Sig.Alias EQU BIOS.Entry + BIOS.Sig.Pos + 10h | ||
|
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| Boot.A20: | ||
| ; CS:BIOS.Sig.Pos has a known, safely-modifable value. | ||
| ; Prepare for testing, by comparing CS:BIOS.Sig.Pos with 0FFFFh:Sig.Alias | ||
| MOV SI,BIOS.Sig.Pos | ||
|
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| MOV AX,0FFFFh ; End of 1 MB | ||
| MOV ES,AX ; In ES | ||
| MOV DI,Sig.Alias | ||
|
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| ; First things first: has it already been done for us? | ||
| CALL .Test ; Test if A20 already on | ||
| JE .End ; Yep! Nothing to do | ||
|
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||
| ; No. OK, maybe the BIOS can help. | ||
| MOV AX,A20.Enable | ||
| INT BIOS.A20.Int ; Using BIOS | ||
|
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| CALL .Test ; Did it work? | ||
| JE .End ; Yep! Nothing more to do | ||
|
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| ; No. OK: the traditional ways are always the best? | ||
| CALL Boot.A20.Switch ; Switch A20 myself | ||
| ; JNZ $ ; Uh oh! ***STOP!*** | ||
|
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| CALL .Test ; Did it work? | ||
| JE .End ; Yep! Nothing more to do | ||
|
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| ; No. Maybe it's a PS/2? | ||
| IN AL,Dev.A20.Fast.Port ; Try Fast A20 | ||
| TEST AL,Dev.A20.Fast.A20 ; Enabled? | ||
| JNZ $ ; Uh oh! Isn't working! ***STOP!*** | ||
| OR AL,Dev.A20.Fast.A20 ; Enable it | ||
| AND AL,~Dev.A20.Fast.Reset ; But NOT Fast Reset! | ||
| OUT Dev.A20.Fast.Port,AL | ||
|
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| CALL .Test ; Did it work? | ||
| JE .End ; Yep! Finally! | ||
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| JMP $ ; No reaction! ***STOP!*** | ||
| Boot.A20.Test: | ||
| MOV DX,[CS:SI] ; Get current value | ||
| CMP DX,[ES:DI] ; Same at end of RAM? | ||
| JNE .Good ; No, so no problem! | ||
|
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| NOT WORD [CS:SI] ; Change current value | ||
| CMP DX,[ES:DI] ; Still same as old? | ||
| JMP .Bad ; No, so problem! | ||
| .Good: | ||
| XOR AX,AX ; Set Z flag | ||
| .Bad: | ||
| RET | ||
|
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| ;------------------------------------------------------------------------------- | ||
|
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| Boot.A20.Switch: | ||
| CALL .Wait ; Wait for 8042 to be ready | ||
| JNZ .Dead ; Uh oh... | ||
|
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| MOV AL,Dev.A20.Ctrl.Write | ||
| OUT Dev.A20.Ctrl.Port,AL ; Tell 8042 we're writing to it | ||
| CALL .Wait ; Wait for acknowledge | ||
| JNZ .Dead ; Uh oh... | ||
|
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| MOV AL,Dev.A20.Data.Enable | ||
| OUT Dev.A20.Data.Port,AL ; Tell 8042 to Enable A20 | ||
| ;............................................................................... | ||
| .Wait: | ||
| XOR CX,CX ; Try a LARGE number of times! | ||
| .Loop: | ||
| IN AL,Dev.A20.Stat.Port ; Wait to write | ||
| TEST AL,Dev.A20.Stat.InFull ; YES, In! It's backwards | ||
| LOOPNZ .Loop ; Nope. Still full | ||
| .Dead: | ||
| RET | ||
|
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| ;------------------------------------------------------------------------------- | ||
|
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||
| Boot.A20.End: |
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| ; | ||
| ; Boot/Boot.inc | ||
| ; | ||
|
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| ; This is the BIOS Boot entry point. It runs in Real Mode, and assumes the | ||
| ; standard BIOS Boot Specification 1.01. | ||
| ; | ||
| ; It performs the following actions: | ||
| ; 1) Loads the rest of the code into RAM; | ||
| ; 2) Gets some information from the soon-to-be-unusable BIOS; | ||
| ; 3) Sets up the PC for Protected Mode; | ||
| ; 4) JMPs to the freshly-loaded Protected Mode code | ||
| ; After that, the memory used to hold this code is avaiable to the system. | ||
| ; | ||
| ; Note that one of the goals of the Boot sector is to jettison itself: | ||
| ; 7C00h is such an awkward location, so ideally after doing all the Real Mode | ||
| ; initialisation, we can JMP to Protected Mode and simply leave this code behind. | ||
|
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| ; To save space, I take advantage of some HORRIBLE things you can do with | ||
| ; assembly language: PUSHing values to fake CALLs, or worse, SELF-MODIFYING CODE! | ||
| ; In Protected Mode, this last is very difficult to organise - and unreliable | ||
| ; with later processors that have on-board caches - so not worth it. | ||
| ; In Real Mode, this can be very useful as a register- and code-saving device! | ||
|
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||
| ; To save space, I've done away with byte-wasting CALLs and RETs for "modular" | ||
| ; programming. Not that modules aren't in and of themselves useful - indeed, | ||
| ; they're still modularised within their own little files - but the result is | ||
| ; simply a stream of bytes to execute. Where I have defined subroutines to be | ||
| ; CALLed, the stream of code has to either JMP over the subroutine's RET, or | ||
| ; a CALL is faked by PUSHing the desired continuation address onto the stack. | ||
|
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| ;------------------------------------------------------------------------------- | ||
| SEGMENT Real VSTART=0 ALIGN=1 | ||
|
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| USE16 ; Real Mode? 16 bits! | ||
|
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||
| ; At this point, DL is probably the drive number of the Boot Drive. | ||
| ; ES:SI is possibly a pointer to the MBR Partition table entry (See Load.inc). | ||
| ; In any case: don't clobber DL, ES or SI before Load.inc! | ||
|
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| %include "Boot/Entry.inc" ; Entry code to initialise important registers | ||
| ;------------------------------------------------------------------------------- | ||
| %include "Boot/CPU.inc" ; Check CPU is (at least) a '386 | ||
| ;------------------------------------------------------------------------------- | ||
| %include "Boot/Load.inc" ; Load Protected Mode code | ||
| ;------------------------------------------------------------------------------- | ||
| %include "Boot/IDT.inc" ; Move IDT to final location | ||
| ;------------------------------------------------------------------------------- | ||
| %include "Boot/RAM.inc" ; Get RAM size | ||
| ;------------------------------------------------------------------------------- | ||
| %include "Boot/A20.inc" ; Enable A20 gate | ||
| ;------------------------------------------------------------------------------- | ||
| %include "Boot/Key.inc" ; Speed up keyboard | ||
| ;------------------------------------------------------------------------------- | ||
| %include "Boot/VGA.inc" ; Switch Video mode | ||
| ;------------------------------------------------------------------------------- | ||
| %include "Boot/PM.inc" ; Switch to Protected Mode | ||
| ;------------------------------------------------------------------------------- | ||
|
|
||
| ; At this point, we still must be inside the first 512-byte Boot sector. | ||
| ; We need to confirm to the BIOS that this sector is a valid Boot sector by | ||
| ; having BIOS.Sig.Value at the correct place. | ||
| ; Note that if the previous code was too large, the following Pad calculation | ||
| ; will underflow and generate an error. | ||
|
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||
| Real.Padding EQU BIOS.Sig.Pos - ($ - $$) | ||
| TIMES Real.Padding DB 00h | ||
|
|
||
| DW BIOS.Sig.Value |
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