_vflat.asm

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;****************************************************************************
;*
;*                  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.
;----------------------------------------------------------------------------