_vflat.asm

BIOS emulator and interface to Realmode X86 Emulator Library Can emulate a PCI Graphic Controller V

;****************************************************************************
;*
;*					SciTech OS Portability Manager Library
;*
;*  ========================================================================
;*
;*    The contents of this file are subject to the SciTech MGL Public
;*    License Version 1.0 (the "License"); you may not use this file
;*    except in compliance with the License. You may obtain a copy of
;*    the License at http://www.scitechsoft.com/mgl-license.txt
;*
;*    Software distributed under the License is distributed on an
;*    "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
;*    implied. See the License for the specific language governing
;*    rights and limitations under the License.
;*
;*    The Original Code is Copyright (C) 1991-1998 SciTech Software, Inc.
;*
;*    The Initial Developer of the Original Code is SciTech Software, Inc.
;*    All Rights Reserved.
;*
;*  ========================================================================
;*
;* 			  Based on original code Copyright 1994 Otto Chrons
;*
;* Language:	80386 Assembler, TASM 4.0 or later
;* Environment:	IBM PC 32 bit protected mode
;*
;* Description:	Low level page fault handler for virtual linear framebuffers.
;*
;****************************************************************************

		IDEAL
		JUMPS

include "scitech.mac"			; Memory model macros

header      _vflat              ; Set up memory model

VFLAT_START		EQU 0F0000000h
VFLAT_END		EQU 0F03FFFFFh
PAGE_PRESENT 	EQU 1
PAGE_NOTPRESENT EQU 0
PAGE_READ 		EQU 0
PAGE_WRITE		EQU 2

ifdef	DOS4GW

;----------------------------------------------------------------------------
; DOS4G/W flat linear framebuffer emulation.
;----------------------------------------------------------------------------

begdataseg  _vflat

; Near pointers to the page directory base and our page tables. All of
; this memory is always located in the first Mb of DOS memory.

PDBR            dd 	0            	; Page directory base register (CR3)
accessPageAddr  dd 	0
accessPageTable dd 	0

; CauseWay page directory & 1st page table linear addresses.

CauseWayDIRLinear dd 0
CauseWay1stLinear dd 0

; Place to store a copy of the original Page Table Directory before we
; intialised our virtual buffer code.

pageDirectory:	resd 1024   		; Saved page table directory

ValidCS			dw	0				; Valid CS for page faults
Ring0CS			dw	0				; Our ring 0 code selector
LastPage		dd	0				; Last page we mapped in
BankFuncBuf:	resb 101 			; Place to store bank switch code
BankFuncPtr		dd	offset BankFuncBuf

INT14Gate:
INT14Offset     dd      0  			; eip of original vector
INT14Selector   dw      0			; cs of original vector

		cextern	_PM_savedDS,USHORT
		cextern	VF_haveCauseWay,BOOL

enddataseg  _vflat

begcodeseg  _vflat              ; Start of code segment

		cextern	VF_malloc,FPTR

;----------------------------------------------------------------------------
; PF_handler64k - Page fault handler for 64k banks
;----------------------------------------------------------------------------
; The handler below is a 32 bit ring 0 page fault handler.  It receives
; control immediately after any page fault or after an IRQ6 (hardware
; interrupt). This provides the fastest possible handling of page faults
; since it jump directly here.  If this is a page fault, the number
; immediately on the stack will be an error code, at offset 4 will be
; the eip of the faulting instruction, at offset 8 will be the cs of the
; faulting instruction.  If it is a hardware interrupt, it will not have
; the error code and the eflags will be at offset 8.
;----------------------------------------------------------------------------
cprocfar	PF_handler64k

; Check if this is a processor exeception or a page fault

		push	eax
		mov		ax,[cs:ValidCS]		; Use CS override to access data
		cmp		[ss:esp+12],ax		; Is this a page fault?
		jne 	@@ToOldHandler		; Nope, jump to the previous handler

; Get address of page fault and check if within our handlers range

		mov     eax,cr2             ; EBX has page fault linear address
		cmp     eax,VFLAT_START		; Is the fault less than ours?
		jb 		@@ToOldHandler		; Yep, go to previous handler
		cmp     eax,VFLAT_END		; Is the fault more than ours?
		jae		@@ToOldHandler		; Yep, go to previous handler

; This is our page fault, so we need to handle it

		pushad
		push	ds
		push    es
		mov		ebx,eax				; EBX := page fault address
		and		ebx,invert 0FFFFh	; Mask to 64k bank boundary
		mov		ds,[cs:_PM_savedDS]; Load segment registers
		mov     es,[cs:_PM_savedDS]

; Map in the page table for our virtual framebuffer area for modification

		mov     edi,[PDBR]      	; EDI points to page directory
		mov     edx,ebx            	; EDX = linear address
		shr     edx,22              ; EDX = offset to page directory
		mov     edx,[edx*4+edi]     ; EDX = physical page table address
		mov     eax,edx
		mov     edx,[accessPageTable]
		or      eax,7
		mov     [edx],eax
		mov     eax,cr3
		mov     cr3,eax				; Update page table cache

; Mark all pages valid for the new page fault area

		mov		esi,ebx				; ESI := linear address for page
		shr     esi,10
		and     esi,0FFFh           ; Offset into page table
		add		esi,[accessPageAddr]
ifdef	USE_NASM
%assign off	0
%rep 16
		or    	[DWORD esi+off],0000000001h	; Enable pages
%assign off	off+4
%endrep
else
off = 0
REPT	16
		or    	[DWORD esi+off],0000000001h	; Enable pages
off = off+4
ENDM
endif

; Mark all pages invalid for the previously mapped area

		xchg	esi,[LastPage]		; Save last page for next page fault
		test	esi,esi
		jz		@@DoneMapping		; Dont update if first time round
ifdef	USE_NASM
%assign off	0
%rep 16
		or    	[DWORD esi+off],0FFFFFFFEh	; Disable pages
%assign off	off+4
%endrep
else
off = 0
REPT	16
		and		[DWORD esi+off],0FFFFFFFEh	; Disable pages
off = off+4
ENDM
endif

@@DoneMapping:
		mov     eax,cr3
		mov     cr3,eax           	; Flush the TLB

; Now program the new SuperVGA starting bank address

		mov		eax,ebx				; EAX := page fault address
		shr     eax,16
		and		eax,0FFh			; Mask to 0-255
		call    [BankFuncPtr]		; Call the bank switch function

		pop     es
		pop     ds
		popad
		pop		eax
		add     esp,4             	; Pop the error code from stack
		iretd                      	; Return to faulting instruction

@@ToOldHandler:
		pop		eax
ifdef	USE_NASM
		jmp far dword [cs:INT14Gate]; Chain to previous handler
else
		jmp		[FWORD cs:INT14Gate]; Chain to previous handler
endif

cprocend

;----------------------------------------------------------------------------
; PF_handler4k  - Page fault handler for 4k banks
;----------------------------------------------------------------------------
; The handler below is a 32 bit ring 0 page fault handler.  It receives
; control immediately after any page fault or after an IRQ6 (hardware
; interrupt). This provides the fastest possible handling of page faults
; since it jump directly here.  If this is a page fault, the number
; immediately on the stack will be an error code, at offset 4 will be
; the eip of the faulting instruction, at offset 8 will be the cs of the
; faulting instruction.  If it is a hardware interrupt, it will not have
; the error code and the eflags will be at offset 8.
;----------------------------------------------------------------------------
cprocfar	PF_handler4k

; Fill in when we have tested all the 64Kb code

ifdef	USE_NASM
		jmp far dword [cs:INT14Gate]; Chain to previous handler
else
		jmp		[FWORD cs:INT14Gate]; Chain to previous handler
endif

cprocend

;----------------------------------------------------------------------------
; void InstallFaultHandler(void *baseAddr,int bankSize)
;----------------------------------------------------------------------------
; Installes the page fault handler directly int the interrupt descriptor
; table for maximum performance. This of course requires ring 0 access,
; but none of this stuff will run without ring 0!
;----------------------------------------------------------------------------
cprocstart	InstallFaultHandler

		ARG     baseAddr:ULONG, bankSize:UINT

		enter_c

		mov		[DWORD LastPage],0	; No pages have been mapped
		mov		ax,cs
		mov		[ValidCS],ax		; Save CS value for page faults

; Put address of our page fault handler into the IDT directly

		sub		esp,6               ; Allocate space on stack
ifdef	USE_NASM
		sidt 	[ss:esp]			; Store pointer to IDT
else
		sidt	[FWORD ss:esp]		; Store pointer to IDT
endif
		pop     ax               	; add esp,2
		pop     eax                 ; Absolute address of IDT
		add     eax,14*8          	; Point to Int #14

; Note that Interrupt gates do not have the high and low word of the
; offset in adjacent words in memory, there are 4 bytes separating them.

		mov     ecx,[eax]   		; Get cs and low 16 bits of offset
		mov     edx,[eax+6]         ; Get high 16 bits of offset in dx
		shl     edx,16
		mov     dx,cx             	; edx has offset
		mov     [INT14Offset],edx	; Save offset
		shr     ecx,16
		mov     [INT14Selector],cx	; Save original cs
		mov     [eax+2],cs          ; Install new cs
		mov     edx,offset PF_handler64k
		cmp		[UINT bankSize],4
		jne		@@1
		mov		edx,offset PF_handler4k
@@1:	mov     [eax],dx          	; Install low word of offset
		shr     edx,16
		mov     [eax+6],dx          ; Install high word of offset

		leave_c
		ret

cprocend

;----------------------------------------------------------------------------
; void RemoveFaultHandler(void)
;----------------------------------------------------------------------------
; Closes down the virtual framebuffer services and restores the previous
; page fault handler.
;----------------------------------------------------------------------------
cprocstart	RemoveFaultHandler

		enter_c

; Remove page fault handler from IDT

		sub		esp,6               ; Allocate space on stack
ifdef	USE_NASM
		sidt 	[ss:esp]			; Store pointer to IDT
else
		sidt	[FWORD ss:esp]		; Store pointer to IDT
endif

		pop     ax               	; add esp,2
		pop     eax                 ; Absolute address of IDT
		add     eax,14*8          	; Point to Int #14
		mov     cx,[INT14Selector]
		mov     [eax+2],cx          ; Restore original CS
		mov     edx,[INT14Offset]
		mov     [eax],dx          	; Install low word of offset
		shr     edx,16
		mov     [eax+6],dx          ; Install high word of offset

		leave_c
		ret

cprocend

;----------------------------------------------------------------------------
; void InstallBankFunc(int codeLen,void *bankFunc)
;----------------------------------------------------------------------------
; Installs the bank switch function by relocating it into our data segment
; and making it into a callable function. We do it this way to make the
; code identical to the way that the VflatD devices work under Windows.
;----------------------------------------------------------------------------