Reinstate memdisk.asm

1 files changed, 418 insertions, 0 deletions

diff --git a/memdisk/memdisk.asm b/memdisk/memdisk.asm
new file mode 100644
index 00000000..b175d711
--- /dev/null
+++ b/memdisk/memdisk.asm
@@ -0,0 +1,418 @@
+; -*- fundamental -*- (asm-mode sucks)
+; $Id$
+; ****************************************************************************
+;
+;  memdisk.asm
+;
+;  A program to emulate an INT 13h disk BIOS from a "disk" in extended
+;  memory.
+;
+;   Copyright (C) 2001  H. Peter Anvin
+;
+;  This program is free software; you can redistribute it and/or modify
+;  it under the terms of the GNU General Public License as published by
+;  the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,
+;  USA; either version 2 of the License, or (at your option) any later
+;  version; incorporated herein by reference.
+; 
+; ****************************************************************************
+
+		org 0h
+
+%define SECTORSIZE_LG2	9		; log2(sector size)
+%define	SECTORSIZE	(1 << SECTORSIZE_LG2)
+
+MyStack		equ 1024
+
+		; Parameter registers definition; this is the definition
+		; of the stack frame.
+%define		P_DS		word [bp+34]
+%define		P_ES		word [bp+32]
+%define		P_EAX		dword [bp+28]
+%define		P_AX		word [bp+28]
+%define		P_AL		byte [bp+28]
+%define		P_AH		byte [bp+29]
+%define		P_ECX		dword [bp+24]
+%define		P_CX		word [bp+24]
+%define		P_CL		byte [bp+24]
+%define		P_CH		byte [bp+25]
+%define		P_EDX		dword [bp+20]
+%define		P_DX		word [bp+20]
+%define		P_DL		byte [bp+20]
+%define		P_DH		byte [bp+21]
+%define		P_EBX		dword [bp+16]
+%define		P_BX		word [bp+16]
+%define		P_BL		byte [bp+16]
+%define		P_BH		byte [bp+17]
+%define		P_EBP		dword [bp+8]
+%define		P_BP		word [bp+8]
+%define		P_ESI		dword [bp+4]
+%define		P_SI		word [bp+4]
+%define		P_EDI		dword [bp]
+%define		P_DI		word [bp]
+
+		section .text
+Int13Start:
+		; See if DL points to our class of device (FD, HD)
+		push dx
+		xor dl,[cs:DriveNo]
+		pop dx
+		js .nomatch		; If SF=0, we have a match here
+		cmp dl,[cs:DriveNo]
+		je .our_drive
+		jb .nomatch		; Drive < Our drive
+		dec dl			; Drive > Our drive, adjust drive #
+.nomatch:
+		jmp far [OldInt13]
+
+.our_drive:
+		mov [cs:Stack],sp
+		mov [cs:SavedAX],ax
+		mov ax,ss
+		mov [cs:Stack+2],ax
+		mov ax,cs
+		mov ss,ax
+		mov sp,MyStack
+		push ds
+		push es
+		mov ds,ax
+		mov es,ax
+		mov ax,[SavedAX]
+		pushad
+		mov bp,sp
+		cmp ah,Int13FuncsMax
+		jae Invalid
+		xor al,al		; AL = 0 is standard entry condition
+		mov di,ax
+		shr di,7
+		call [Int13Funcs+di]
+
+Done:		; Standard routine for return
+		mov [LastStatus],ah
+		mov P_AX,ax
+		cmp ah,1
+DoneWeird:
+		setnb al		; AL <- (AH > 0) ? 1 : 0 (CF)
+		lds bx,[Stack]		; DS:BX <- Old stack pointer
+		mov [bx+4],al		; Low byte of old FLAGS -> arithmetric flags
+		popad
+		pop es
+		pop ds
+		lss sp,[cs:Stack]
+		iret
+
+Reset:
+		; Reset affects multiple drives, so we need to pass it on
+		pop ax			; Drop return address
+		mov [LastStatus], byte 0
+		popad
+		pop es
+		pop ds
+		lss sp,[cs:Stack]
+		and dl,80h		; Clear all but the type bit
+		jmp far [OldInt13]
+
+Invalid:
+		mov ax,0100h		; Unsupported function
+		ret
+
+GetDriveType:
+		pop ax			; Drop return address
+		mov ah,[DriveNo]
+		shr ah,7
+		or ah,02h		; CF = 0
+		mov P_AH,ah
+		mov [LastStatus],byte 0	; Success, but AH returns a value
+		jmp short DoneWeird
+
+GetStatus:
+		mov ah,[LastStatus]	; Copy last status
+		ret
+
+CheckIfReady:				; These are always-successful noop functions
+Recalibrate:
+InitWithParms:
+DetectChange:
+success:
+		xor ax,ax		; Always successful
+		ret
+
+Read:
+		call setup_regs
+do_copy:
+		call bcopy
+		movzx ax,P_AL		; AH = 0, AL = transfer count
+		ret
+
+Write:
+		call setup_regs
+		xchg esi,edi
+		jmp short do_copy
+
+		; These verify one sector only
+Seek:
+		mov P_AL,1
+
+		; Verify integrity; just bounds-check
+Verify:
+		call setup_regs		; Returns error if appropriate
+		jmp short success	
+
+GetParms:
+		; We need to get the "number of drives" from the BIOS
+		mov dl,P_DL
+		inc dl			; The drive whose number we're stealing
+		mov ah,08h
+		int 13h
+		inc dl			; Add ourselves to the count
+		mov P_DL,dl		; Drive count
+		mov P_DI,di		; Steal the diskette parameter table if applicable
+		mov ax,es
+		mov P_ES,ax
+		mov bl,[DriveType]
+		mov P_BL,bl
+		mov ax,[Cylinders]
+		dec ax			; We report the highest #, not the count
+		or ah,[Sectors]
+		xchg al,ah
+		mov P_CX,ax
+		mov al,[Heads]
+		dec al
+		mov P_DH,al
+		xor ax,ax
+		ret
+
+		; Convert a CHS address in CX/DH into an LBA in EAX
+chstolba:
+		xor ebx,ebx
+		mov bl,cl		; Sector number
+		and bl,3Fh
+		dec bx
+		mov si,dx
+		mov ax,[Heads]
+		shr cl,6
+		xchg cl,ch		; Now CX <- cylinder number
+		mul cx			; DX:AX <- AX*CX
+		shr si,8		; SI <- head number
+		add ax,si
+		adc dx,byte 0
+		shl edx,16
+		or eax,edx
+		mul dword [Sectors]
+		add eax,ebx
+		ret
+
+		; Set up registers as for a "Read", and compares against disk size
+setup_regs:
+		call chstolba
+		movzx edi,P_BX		; Get linear address of target buffer
+		movzx ecx,P_ES
+		shr ecx,4
+		add edi,ecx
+		movzx ecx,P_AL
+		lea ebx,[eax+ecx]
+		mov esi,eax
+		shr esi,SECTORSIZE_LG2
+		add esi,[DiskBuf]
+		cmp ebx,[DiskSize]
+		jae .overrun
+		shr ecx,SECTORSIZE_LG2-1
+		ret
+
+.overrun:	pop ax			; Drop return address
+		mov ax,0400h		; Sector not found
+		ret
+
+int15_e820:
+		cmp edx,534D4150h
+		jne near oldint15
+		cmp ecx,20		; Need 20 bytes
+		jb err86
+		push edx		; "SMAP"
+		push esi
+		push edi
+		and ebx,ebx
+		jne .renew
+		mov ebx,[E820Table]
+.renew:		mov esi,ebx
+		xor edi,edi
+		mov di,cs
+		shr di,4
+		add edi,E820Buf
+		mov ecx,24/2
+		call bcopy
+		add ebx, byte 12
+		pop edi
+		pop esi
+		mov eax,[cs:E820Buf]
+		mov [es:di],eax
+		mov eax,[cs:E820Buf+4]
+		mov [es:di+4],eax
+		mov eax,[cs:E820Buf+12]
+		mov [es:di+8],eax
+		mov eax,[cs:E820Buf+16]
+		mov [es:di+12],eax
+		mov eax,[cs:E820Buf+8]
+		mov [es:di+16],eax
+		cmp dword [cs:E820Buf+20], byte -1
+		jne .notdone
+		xor ebx,ebx		; Done with table
+.notdone:
+		pop eax			; "SMAP"
+		mov ecx,20		; Bytes loaded
+int15_success:
+		mov byte [bp+12], 02h	; Clear CF
+		pop bp
+		iret
+
+err86:
+		mov byte [bp+12], 03h	; Set CF
+		mov ah,86h
+		pop bp
+		iret
+
+Int15Start:
+		push bp
+		mov bp,sp
+		cmp ax,0E820h
+		je near int15_e820
+		cmp ax,0E801h
+		je int15_e801
+		cmp ax,0E881h
+		je int15_e881
+		cmp ah,88h
+		je int15_88
+oldint15:	pop bp
+		jmp far [cs:OldInt15]
+		
+int15_e801:
+		mov ax,[cs:Mem1MB]
+		mov cx,ax
+		mov bx,[cs:Mem16MB]
+		mov dx,ax
+		jmp short int15_success
+
+int15_e881:
+		mov eax,[cs:Mem1MB]
+		mov ecx,eax
+		mov ebx,[cs:Mem16MB]
+		mov edx,eax
+		jmp short int15_success
+
+int15_88:
+		mov ax,[cs:MemInt1588]
+		jmp short int15_success
+
+;
+; Routine to copy in/out of high memory
+; esi = linear source address
+; edi = linear target address
+; ecx = 16-bit word count 
+;
+; Assumes cs = ds = es
+;
+bcopy:
+		push eax
+		push ebx
+		push edx
+		push ebp
+		push esi
+		push edi
+.copy_loop:
+		push ecx
+		cmp ecx,8000h
+		jna .safe_size
+		mov ecx,8000h
+.safe_size:
+		push ecx
+		mov eax, esi
+		mov [Mover_src1], si
+		shr eax, 16
+		mov [Mover_src1+2], al
+		mov [Mover_src2], ah
+		mov eax, edi
+		mov [Mover_dst1], di
+		shr eax, 16
+		mov [Mover_dst1+2], al
+		mov [Mover_dst2], ah
+		mov si,Mover
+		mov ah, 87h
+		int 15h
+		pop eax
+		pop ecx
+		pop edi
+		pop esi
+		jc .error
+		lea esi,[esi+2*eax]
+		lea edi,[edi+2*eax]
+		sub ecx, eax
+		jnz .copy_loop
+		; CF = 0
+.error:
+		pop ebp
+		pop edx
+		pop ebx
+		pop eax
+		ret
+
+		section .data
+Int13Funcs	dw Reset		; 00h - RESET
+		dw GetStatus		; 01h - GET STATUS
+		dw Read			; 02h - READ
+		dw Write		; 03h - WRITE
+		dw Verify		; 04h - VERIFY
+		dw Invalid		; 05h - FORMAT TRACK
+		dw Invalid		; 06h - FORMAT TRACK AND SET BAD FLAGS
+		dw Invalid		; 07h - FORMAT DRIVE AT TRACK
+		dw GetParms		; 08h - GET PARAMETERS
+		dw InitWithParms	; 09h - INITIALIZE CONTROLLER WITH DRIVE PARAMETERS
+		dw Invalid		; 0Ah
+		dw Invalid		; 0Bh
+		dw Seek			; 0Ch - SEEK TO CYLINDER
+		dw Reset		; 0Dh - RESET HARD DISKS
+		dw Invalid		; 0Eh
+		dw Invalid		; 0Fh
+		dw CheckIfReady		; 10h - CHECK IF READY
+		dw Recalibrate		; 11h - RECALIBRATE
+		dw Invalid		; 12h
+		dw Invalid		; 13h
+		dw Invalid		; 14h
+		dw GetDriveType		; 15h - GET DRIVE TYPE
+		dw DetectChange		; 16h - DETECT DRIVE CHANGE
+Int13FuncsEnd	equ $
+Int13FuncsMax	equ (Int13FuncsEnd-Int13Funcs) >> 1
+
+DriveNo		db 0			; Our drive number
+DriveType	db 0			; Our drive type (floppies)
+LastStatus	db 0			; Last return status
+
+		alignb 4, db 0
+Cylinders	dw 0			; Cylinder count
+Heads		dw 0			; Head count
+Sectors		dd 0			; Sector count (zero-extended)
+DiskSize	dd 0			; Size of disk in blocks
+DiskBuf		dd 0			; Linear address of high memory disk
+
+E820Table	dd 0			; E820 table in high memory
+Mem1MB		dd 0			; 1MB-16MB memory amount (1K)
+Mem16MB		dd 0			; 16MB-4G memory amount (64K)
+MemInt1588	dw 0			; 1MB-65MB memory amount (1K)
+
+		alignb 8, db 0
+Mover		dd 0, 0, 0, 0		; Must be zero
+		dw 0ffffh		; 64 K segment size
+Mover_src1:	db 0, 0, 0		; Low 24 bits of source addy
+		db 93h			; Access rights
+		db 00h			; Extended access rights
+Mover_src2:	db 0			; High 8 bits of source addy
+Mover_dst1:	db 0, 0, 0		; Low 24 bits of target addy
+		db 93h			; Access rights
+		db 00h			; Extended access rights
+Mover_dst2:	db 0			; High 8 bits of source addy
+
+		section .bss
+OldInt13	resd 1			; INT 13h in chain
+OldInt15	resd 1			; INT 15h in chain
+Stack		resd 1			; Saved SS:SP on invocation
+E820Buf		resd 6			; E820 fetch buffer
+SavedAX		resw 1			; AX saved during initialization