ProfitPress Mega CDROM2 …eeware (MSDOS)(1992)(Eng)/ProfitPress-MegaCDROM2.B6I/MISC/GNU/SH164AS.ZIP/SHELL/SH0.ASM

Assembly Source File | 1992-02-28 | 29.5 KB | 1,773 lines

    TITLE   sh0.asm
    NAME    sh0
    .8087

; MS-DOS SHELL - Swapper
;
; MS-DOS SHELL - Copyright (c) 1990 Data Logic Limited
;
; This code is subject to the following copyright restrictions:
;
; 1.  Redistribution and use in source and binary forms are permitted
;     provided that the above copyright notice is duplicated in the
;     source form and the copyright notice in file sh6.c is displayed
;     on entry to the program.
;
; 2.  The sources (or parts thereof) or objects generated from the sources
;     (or parts of sources) cannot be sold under any circumstances.
;
;    $Header: D:/SRC/SHELL/RCS/sh0.asm 1.10 90/05/31 17:46:31 MS_user Exp $
;
;    $Log:    sh0.asm $
;    Revision 1.10  90/05/31  17:46:31  MS_user
;    Enasure that correct block zero is written for partial write
;
;    Revision 1.9  90/05/31  10:04:56  MS_user
;    Implement partial write on disk swapping
;
;    Revision 1.8  90/04/25  22:32:31  MS_user
;    Fix missing disk full check on writing swap file
;
;    Revision 1.7  90/04/11  12:54:38  MS_user
;    Fix non-disk device name print in CEH
;
;    Revision 1.6  90/03/26  04:31:01  MS_user
;    Remove original Interrupt 24 save address
;
;    Revision 1.5  90/03/26  04:12:38  MS_user
;    Add Full Interrupt 24 handler
;
;    Revision 1.4  90/03/05  13:47:05  MS_user
;    Add XMS driver
;
;    Revision 1.3  90/02/22  16:50:23  MS_user
;    Add XMS Driver support
;
;    Revision 1.2  90/02/14  04:45:58  MS_user
;    Add Interrupt 24 processing and clean up interrupt 0 and 23 processing
;
;    Revision 1.1  90/01/25  13:43:36  MS_user
;    Initial revision
;
;

;
; Segment declarations
;

SH0_TEXT    segment word public 'CODE'
SH0_TEXT    ends

_DATA        segment word public 'DATA'
_DATA        ends

CONST        segment word public 'CONST'
CONST        ends

_BSS        segment word public 'BSS'
_BSS        ends

DGROUP        group    CONST, _BSS, _DATA

C_ETEXT        segment word public 'ENDCODE'
C_ETEXT        ends

;
; Declare external functions and data
;
    extrn    _raise:far
    extrn    __maperror:far
    extrn    _errno:word
    extrn    __psp:word

;
; Declare end of text variable.  The ENDCODE segment appears to be the last
; code segment loaded by the Microsoft loader
;

C_ETEXT        segment word public 'ENDCODE'
        public    cetext
cetext        equ    $
C_ETEXT        ends

;
; Start of the spawn function
;

SH0_TEXT    segment
        assume  cs: SH0_TEXT, ds: NOTHING, ss: DGROUP

;
; For this function, all the code and data space are in the code space
;
        public    _cmd_line
        public    _path_line
        public    _SW_intr
        public    _SW_Blocks
        public    _SW_SBlocks
        public    _SW_fp
        public    _SW_I0_V
        public    _SW_I23_V
        public    _SW_EMstart
        public    _SW_Mode
        public    _SW_EMSFrame
        public    _SW_Int24
        public    _SW_XMS_Driver
        public    _SW_XMS_Gversion
        public    _SW_XMS_Allocate
        public    _SW_XMS_Free
        public    _etext
        public    _SW_Pwrite


_cmd_line    db    129 dup (?)    ; Command line
_path_line    db    80 dup (?)    ; Path line
_etext        dw    seg cetext    ; End of text segment
_SW_Blocks    dw    0        ; Number of blocks to read/write
_SW_SBlocks    dw    0        ; Short Number of blocks to read/write
_SW_fp        dw    0        ; File ID
_SW_Pwrite    dw    0        ; Partial write to disk?
_SW_I0_V    dd    0        ; Our Interrupt Zero address
_SW_I23_V    dd    0        ; Our Interrupt 23 address
_SW_EMstart    dd    0100000H    ; Default Extended Mem start
_SW_Mode    dw    0        ; Type of swapping to do
                    ;   1 - disk
                    ;   2 - Extended memory
                    ;   3 - EMS driver
                    ;   4 - XMS driver
_SW_EMSFrame    dw    0        ; EMS Frame segment
_SW_intr    dw    0        ; Interrupt 23 detected.
_SW_XMS_Driver    dd    0        ; XMS Driver Interface

;
; Some addition variables
;

SW_LMstart    dd    0        ; Low Mem start for Extended Mem swap
N_mcb        dw    0        ; Start write address
Result        dw    0        ; Return value
InShell        db    0        ; In shell flag for Interrupt 23

;
; Stack save pointers
;

S_ss        dw    0            ; Save Stack pointers
S_sp        dw    0
S_di        dw    0            ; Save DI, SI
S_si        dw    0
S_ds        dw    0            ; Save the original DS

;
; Two blank FCB
;

FCB1        dw    16    dup (?)
FCB2        dw    16    dup (?)

;
; XMS Driver Move structure
;

XMS_DIF        equ    $
XMS_Length    dd    0            ; Number of bytes
XMS_SHandle    dw    0            ; Source Handler
XMS_Soffset    dd    0            ; Source Offset
XMS_DHandle    dw    0            ; Destination Handler
XMS_Doffset    dd    0            ; Destination Offset

;
; Extended Memory Global Descriptor tables
;
        org    XMS_DIF
GD_table    equ    $
GDT_Dummy    dw    4    dup (0)        ; Dummy
GDT_self    dw    4    dup (0)        ; For self
GDT_src        equ    $            ; Source
        dw    04000H            ; Length - 16K bytes
GDT_src_low    dw    0            ;     Low Order address
GDT_src_high    db    0            ;     High Order address
        db    093h            ;     Access Rights
        dw    0            ;     Reserved
GDT_dest    equ    $            ; Destination
        dw    04000H            ;     Length - 16K bytes
GDT_dest_low    dw    0            ;     Low Order address
GDT_dest_high    db    0            ;     High Order address
        db    093h            ;     Access Rights
        dw    0            ;     Reserved
GDT_bios    dw    4    dup (0)        ; Bios
GDT_stack    dw    4    dup (0)        ; Stack

;
; Execute interrupt structure
;

exec_parms    equ    $
exec_env    dw    0
        dw    offset _cmd_line    ; Command line address
exec_cseg    dw    ?
        dw    offset FCB1        ; FCB1 address
exec_f1seg    dw    ?
        dw    offset FCB2        ; FCB1 address
exec_f2seg    dw    ?

Swap_PANIC    db    'PANIC: Swap file re-load error - REBOOT', 0aH, 0dH
        db    '$'

Swap_DZERO    db    'PANIC: Divide by zero', 0aH, 0dH
        db    '$'

;
; OK - exec requires a local stack, cause some programs overwrite it
;
        even
        db    398 dup (0)
Local_Stack:
        dw    0

;
; Code starts
;
    public    _SA_spawn

_SA_spawn    proc    far

    push    bp
    mov    bp, sp

;
; Entry Offsets
;
;    Environment      = 6
;

    mov    word ptr cs:S_di, di        ; Save registers
    mov    word ptr cs:S_si, si
    mov    word ptr cs:S_ds, ds

;
; Set up to ingnore Control C interrupts
;

    push    ds
    mov    ax, 02523H        ; Set Control C Interrupt
    mov    dx, offset SA_IRET
    push    cs
    pop    ds
    mov    byte ptr cs:InShell, 0    ; Set In shell flag for Interrupt 23
    int    021H

    mov    ax, 02500H        ; Set Divide Zero Interrupt
    mov    dx, offset SA_DZERO
    push    cs
    pop    ds
    int    021H

    pop    ds

;
; Save the length of the current MCB block;
;

    mov    ax, word ptr ds:__psp
    dec    ax
    mov    word ptr cs:N_mcb, ax        ; Save MCB address for swap out

; Calculate low mem start for extended memory

    mov    bx, ax                ; Save copy
    mov    cl, 4                ; mult low order by 16
    shl    ax, cl
    mov    word ptr cs:SW_LMstart, ax    ; Save low order
    mov    cl, 12                ; div by 16 ** 3
    shr    bx, cl
    mov    byte ptr cs:SW_LMstart + 2, bl    ; Save low order

;
; Set up Environment segment in execute structure
;

    mov    bx, cs
    mov    ax, offset Env_OWrite
    mov    cl, 4
    shr    ax, cl
    add    ax, bx
    mov    word ptr cs:exec_env, ax    ; Save Env seg.

;
; Set up rest of execute structure
;

    mov    word ptr cs:exec_cseg, cs    ; Command line address
    mov    word ptr cs:exec_f1seg, cs    ; FCB 1 address
    mov    word ptr cs:exec_f2seg, cs    ; FCB 2 address

;
; Generate the FCBs
;

    mov    ax, cs        ; Set up segments
    mov    ds, ax
    mov    es, ax

    mov    ax, 02901H    ; Set up FCB interrupt
    mov    si, offset _cmd_line + 1
    mov    di, offset FCB1    ; FCB 1;

    int    021H        ; Execute the interrupt

    mov    ax, cs        ; Set up segment
    mov    es, ax

    mov    ax, 02901H    ; Reset AX cause errors are ignored
    mov    di, offset FCB2    ; FCB 2;

    int    021H        ; Execute the interrupt

;
; Copy out to the swap file
;

    mov    bx, word ptr cs:_SW_fp        ; Load file handler
    mov    si, word ptr cs:_SW_Blocks    ; Load Number of blocks to read
    mov    ax, word ptr cs:N_mcb        ; Load the start address

;
;  Check for Partial write on disk swap file
;

    cmp    word ptr cs: _SW_Mode, 1    ; Partial disk write ?
    jnz    SPart_Write
    cmp    word ptr cs: _SW_Pwrite, 0
    jz    SPart_Write

    mov    si, word ptr cs:_SW_SBlocks    ; Load Number of blocks to read
    mov    ax, word ptr cs:_etext        ; Load the start address

SPart_Write:
    push    ax

; load up extended memory GDT for destination

    mov    ax, word ptr cs:_SW_EMstart
    mov    dl, byte ptr cs:_SW_EMstart + 2
    call    $GDT_dest_load

;
; set up DS register with start of start copy
;

    pop    ax
    mov    ds, ax
    mov    ax, word ptr cs:SW_LMstart     ; Load Full start address
    mov    dl, byte ptr cs:SW_LMstart + 2
    call    $GDT_src_load

;
; Check for end of copy - BX contains the file handler for disk write
;

$Write_loop:
    or    si, si
    jnz    $Write_L1
    jmp    $Write_Complete

; OK - Copy next 0x4000 bytes - switch on device

$Write_L1:
    mov    ax, word ptr cs: _SW_Mode
    dec    ax
    jz    $W_disk
    dec    ax
    jnz    $Write_L2
    jmp    $W_extend
$Write_L2:
    dec    ax
    jnz    $W_xms
    jmp    $W_expand

;
; Write to XMS driver.  In this case, we do one write and let the driver
; sort out the blocking
;
$W_xms:
    xor    ax, ax
    mov    word ptr cs:XMS_SHandle, ax    ; Source - normal memory
    mov    word ptr cs:XMS_DHandle, bx    ; Dest - XMS

    mov    word ptr cs:XMS_Doffset, ax    ; Dest offset - zero
    mov    word ptr cs:XMS_Doffset + 2, ax

    mov    word ptr cs:XMS_Soffset, ax    ; Source offset DS:0
    mov    ax, ds
    mov    word ptr cs:XMS_Soffset + 2, ax

;
; Set up number of bytes SW_Block * 16 * 1024
;

    mov    ax, si
    mov    dx, si
    mov    cl, 14
    shl    ax, cl
    mov    cl, 2
    shr    dx, cl
    mov    word ptr cs:XMS_Length, ax    ; Load number of bytes
    mov    word ptr cs:XMS_Length + 2, dx

    mov    ah, 0BH                ; Set up parameters
    mov    dx, cs
    mov    ds, dx
    mov    si, offset XMS_DIF
    call    cs:[_SW_XMS_Driver]
    or    ax, ax
    jnz     $Write_Complete

; XMS error - abort

    mov    ah, bl
    jmp    $Write_error

;
; Write to disk
;
$W_disk:
    call    $Write_disk

; Increment counter

$Write_Incr:
    dec    si            ; Decrement block count
    mov    ax, ds            ; Increment offset
    add    ax, 0400H
    mov    ds, ax
    jmp    $Write_loop

; Write to extended memory

$W_extend:
    call    $Write_extend
    jc    $Write_error        ; NO - abort

    dec    si            ; Decrement block count
    call    $Inc_Extend
    jmp    $Write_loop

; Write to expanded memory
;    BX - handler
;    SI - count
;    DS - source segment
;
$W_expand:
    call    $map_ems_page        ; Map in the current EMS page
    jnz    $Write_error

    push    ds            ; Save DS and SI
    push    si
    mov    es, word ptr cs:_SW_EMSFrame    ; Set Dest Seg
    xor    si, si            ; Clear start
    xor    di, di
    mov    cx, 02000H        ; move 16K
    pushf                ; Save direction flag
    cld
    rep movsw
    popf                ; Restore direction flag
    pop    si            ; And DS, SI
    pop    ds
    jmp    $Write_Incr        ; Increment DS and dec SI

;
; Error - abort.  The error code is in AH.
;

$Write_error:
    mov    ds, word ptr cs:S_ds    ; Restore DS
    mov    al, ah
    xor    ah, ah
    mov    word ptr ds:_errno, ax    ; Save error code

$Write_Error1:
    mov    ax, 0FFFEH
    jmp    $SA_spawn_Exit        ; Exit

;
; Swap file is now written, set up environment.  If this was a partial
; write, we need to write the first 4K.
;

$Write_Complete:
    cmp    word ptr cs: _SW_Mode, 1    ; Partial disk write ?
    jnz    S1Part_Write
    cmp    word ptr cs: _SW_Pwrite, 0
    jz    S1Part_Write

    mov    ax, 04200H            ; Set seek
    xor    dx, dx
    xor    cx, cx
    int    021H
    jnc    $Write_C1            ; Abort - swap file error
    jmp    $Map_error

$Write_C1:
    mov    ax, word ptr cs:N_mcb        ; Load the start address
    mov    ds, ax
    call    $Write_disk

S1Part_Write:
    mov    ds, word ptr cs:exec_env    ; Load Env seg.
    xor    si, si                ; Clear start offset

;
; Copy into Env Seg
;

$Copy_Env:
    les    bx, dword ptr ss:[bp + 6]    ; Check for end of loop
    mov    ax, word ptr es:[bx + 0]
    or    ax, word ptr es:[bx + 2]
    je    $Copy_End

;
; Save start address
;
    add    word ptr ss:[bp + 6], 4        ; Increment environment by 4

    mov    cx, word ptr es:[bx + 0]    ; Load address of cur Env string
    mov    ax, word ptr es:[bx + 2]    ; into es:bx
    mov    es, ax
    mov    bx, cx

;
; Copy this value
;

$Copy_Val:
    mov    al, byte ptr es:[bx]    ; Copy across
    mov    byte ptr ds:[si], al
    inc    bx            ; Increment pointers
    inc    si
    or    al, al
    jne    $Copy_Val
    jmp    $Copy_Env

;
; Set up exec parameter block     - DS is on stack
;
$Copy_End:
    xor    ax, ax
    mov    word ptr ds:[si], ax    ; Terminate environment
    add    si, 2

;
; Set up new program length
;
    add    si, 16            ; Round up paras
    mov    dx, si            ; Save end offset in DX
    mov    bx, ds

    mov    cl, 4
    shr    si, cl            ; # paras used by Env
    add    si, bx            ; End para number

    mov    bx, word ptr cs:N_mcb    ; Load our MCB address in BX
    mov    ax, bx
    inc    ax
    sub    si, ax
    mov    cx, si            ; Save new max paras in CX

;
; Use interrupt 4a to shrink memory.  First release all memory above us.
;
    push    ax
    push    cx            ; Save Max paras and location
    mov    ds, bx            ; Set up the segement for MCB
    mov    cx, word ptr ds:3    ; Get the MCB length

; Are we the only one in the chain?

    cmp    byte ptr ds:0, 'Z'    ; End of chain ?
    jz    $Shrink_First

;
; Loop round releasing memory blocks
;
;    CX - original length of block;
;    DS - segement of the previous block
;
$Shrink_Next:
    mov    ax, ds            ; Move to the next block
    add    cx, ax
    inc    cx
    mov    ds, cx

    cmp    byte ptr ds:0, 'Z'    ; End of chain ?
    jz    $Shrink_First

    mov    cx, word ptr ds:3    ; Save the length of this block

    mov    ax, ds            ; Advance to the block itself
    inc    ax
    mov    es, ax            ; Set up Block address

    mov    ah, 049H
    int    021H
    jmp    $Shrink_Next

;
;    Shrink the PSP segment
;

$Shrink_First:
    pop    cx
    pop    ax
        mov    es, ax            ; Set PSP address
    mov    bx, cx            ; Set max length
    mov    ah, 04aH
    int    021H

;
; Execute function
;

    mov    word ptr cs: S_sp, sp    ; Save the current stack
    mov    word ptr cs: S_ss, ss

;
; Move to the local stack so that it doesn't get overwritten.
;
    mov    ax, cs
    cli
    mov    sp, offset Local_Stack
    mov    ss, ax
    sti

; Clear out Interrupts

    mov    ah, 00bH        ; Check Keyboard status
    int    021H

;
;  Check for interrupt 23 detected
;
    mov    ax, word ptr cs:_SW_intr
    or    ax, ax
    jz    $I23_Cf            ; No - continue;

;
; Interrupt 23 detected - abort
;
    mov    ax, cs            ; Set up for reload
    cli
    mov    sp, offset Local_Stack
    mov    ss, ax
    sti

    mov    ds, word ptr cs:S_ds    ; Restore DS
    xor    ax, ax
    jmp    $Exec_Complete

;
; No interrupts - continue
;
$I23_Cf:
    mov    ax, cs            ; Set up segments
    mov    es, ax
    mov    ds, ax

    mov    ax, 04b00H        ; Load and execute function
    mov    dx, offset _path_line    ; Load path
    mov    bx, offset exec_parms    ; Load the execute structure
    mov    byte ptr cs:InShell, 1    ; Set not In shell flag for Interrupt 23
    int    021H
    mov    byte ptr cs:InShell, 0    ; Set In shell flag for Interrupt 23

; Disable interrupts while we restore the stack to the local one

    mov    ax, cs
    cli
    mov    sp, offset Local_Stack
    mov    ss, ax
    sti

;
; Did an error occur?
;
    jnc    $Exec_OK

;
; Error
;

$Map_error:
    mov    ds, word ptr cs:S_ds    ; Restore DS
    mov    ah, al
    call    far ptr __maperror    ; Map the error

$Exec_Error:
    mov    ax, 0FFFFH
    jmp    $Exec_Complete

;
; No - get the exit code and check for interrupts
;

$Exec_OK:
    mov    ax, 04d00H
    int    021H
    dec    ah            ; Interrupt termination ?
    jnz    $Exec_OK1

    inc    word ptr ds:_SW_intr    ; Set Interrupt 23 detected.

$Exec_OK1:
    xor    ah, ah

;
; Save the result code
;

$Exec_Complete:
    mov    word ptr cs:Result, ax        ; Save response

;
; Very Dangerous - Restore Environment
;
;     Seek to 0x4000 in file
;
    mov    bx, word ptr cs:_SW_fp        ; Load File Handler
    mov    ax, word ptr cs: _SW_Mode    ; Skip if not disk
    dec    ax
    jnz    $Seek_OK

; Seek in file to skip 16K

    mov    dx, 04000H
    call    $Seek_Disk

;
;     Load from N_mcb:0x4000 to end of file.
;

$Seek_OK:
    mov    si, word ptr cs:_SW_Blocks    ; Load number of transfers
    dec    si                ; Skip first block

;
; set up ES register with start of load
;
    mov    ax, word ptr cs:N_mcb    ; Load the start address
    add    ax, 0400H
    mov    ds, ax

; load up extended memory GDT for destination

    call    $GDT_reload
    call    $Inc_Extend            ; Increment addresses by 16K

;
; Check for end of copy    - BX - File Handler for disk
;

$Read_loop:
    or    si, si
    je    $Read_Complete

; OK - Copy next 0x4000 bytes - switch on device

    mov    ax, word ptr cs: _SW_Mode
    dec    ax
    jz    $R_disk
    dec    ax
    jz    $R_extend
    dec    ax
    jz    $R_expand

;
; Read from XMS driver.  In this case, we do one read and let the driver
; sort out the blocking
;
    call    $Read_XMS
    jmp     $Read_Complete

; Read from disk

$R_disk:
    call    $Read_disk
    jmp    $Read_loop

; Read from extended memory

$R_extend:
    call    $Read_extend
    jmp    $Read_loop

; Read from expanded memory

$R_expand:
    call    $Read_EMS
    jmp    $Read_loop

;
; Re-load is now complete, Restore original stack which has just been
; reloaded.  BX contains FP
;

$Read_Complete:
    cli
    mov    sp, word ptr cs: S_sp        ; Save the current stack
    mov    ss, word ptr cs: S_ss
    sti

;  Save exit code

    push    word ptr cs:Result        ; Save response
    push    word ptr cs:_SW_intr        ; and interrupt flag

;
; Read in the first block - BX - File Handler
;

    mov    ax, word ptr cs: _SW_Mode    ; Skip if not disk
    dec    ax
    jnz    $Seek1_OK

; Seek to 0 in file

    xor    dx, dx
    call    $Seek_Disk

;
;     Load one block at N_mcb:0x0000
;
$Seek1_OK:
    mov    ds, word ptr cs:N_mcb        ; Load the start address
    call    $GDT_reload            ; Load the GDT for extend mem

    mov    ax, word ptr cs: _SW_Mode    ; Skip if not disk
    dec    ax
    jz    $R1_Disk
    dec    ax
    jz    $R1_Extend
    dec    ax
    jz    $R1_Expand

    mov    si, 1                ; Read one block
    call    $Read_XMS
    jmp    $Read1_OK

$R1_Disk:
    call    $Read_disk
    jmp    $Read1_OK

$R1_Extend:
    call    $Read_extend
    jmp    $Read1_OK

$R1_Expand:
    mov    si, word ptr cs:_SW_Blocks    ; Read first block
    call    $Read_EMS

;
; Complete - load error code and return
;

$Read1_OK:
    pop    word ptr cs:_SW_intr        ; Restore interrupt flag
    pop    ax

;
; Exit function - Restore Control Interrupt handler
;

$SA_spawn_Exit:
    push    ax                ; Save exit code
    mov    ax, 02523H            ; Set Control C Interrupt
    mov    dx, word ptr cs:_SW_I23_V
    mov    ds, word ptr cs:_SW_I23_V + 2
    int    021H

    mov    ax, 02500H            ; Set Divide Zero Interrupt
    mov    dx, word ptr cs:_SW_I0_V
    mov    ds, word ptr cs:_SW_I0_V + 2

;

    mov    di, word ptr cs:S_di        ; Restore saved registers
    mov    si, word ptr cs:S_si
    mov    ds, word ptr cs:S_ds

; If interrupt 23 detected - raise the flag

    mov    ax, word ptr cs:_SW_intr    ; Set Interrupt 23 detected.
    or    ax, ax
    jz    $SA_Exit1

    mov    ax, 02H
    push    ax                ; Set SIGINT
    call    _raise
    add    sp, 2

$SA_Exit1:
    pop    ax                ; Restore result
    mov    sp, bp
    pop    bp
    ret

_SA_spawn    endp

;
; READ XMS DRIVER FUNCTION
;
;    BX - file handler
;    SI - Block count
;    DS - Output data segement
;
$Read_XMS    proc    near
    xor    ax, ax
    mov    word ptr cs:XMS_SHandle, bx    ; Source - XMS
    mov    word ptr cs:XMS_DHandle, ax    ; Dest - normal memory

    mov    word ptr cs:XMS_Soffset, ax    ; Source offset - zero
    mov    word ptr cs:XMS_Soffset + 2, ax

    mov    word ptr cs:XMS_Doffset, ax    ; Dest offset DS:0
    mov    ax, ds
    mov    word ptr cs:XMS_Doffset + 2, ax

    cmp    si, 1                ; If first block, the
    jz    $Read_X1            ; source offset is
                        ; 4000H
    mov    word ptr cs:XMS_Soffset, 04000H

;
; Set up number of bytes: si * 16 * 1024
;

$Read_X1:
    mov    ax, si
    mov    dx, si
    mov    cl, 14
    shl    ax, cl
    mov    cl, 2
    shr    dx, cl
    mov    word ptr cs:XMS_Length, ax    ; Load number of bytes
    mov    word ptr cs:XMS_Length + 2, dx

    mov    ah, 0BH                ; Set up parameters
    mov    dx, cs
    mov    ds, dx
    mov    si, offset XMS_DIF
    call    cs:[_SW_XMS_Driver]
    or    ax, ax
    jnz     $Read_XMS1
    jmp    Load_Error            ; XMS error - abort

$Read_XMS1:
    ret

$Read_XMS    endp

;
; WRITE DISK FUNCTION
;
;    BX - file handler
;    SI - Block count
;    DS - Output data segement
;

$Write_disk    proc    near

    mov    ax, 04000H        ; Set up to write
    mov    cx, ax            ; Load count
    xor    dx, dx            ; Clear start address
    push    bx            ; Save FP
    push    si            ; Save count and Data Segment

    int    021H            ; Write the data

    pop    si            ; Restore Regs
    pop    bx
    jnc    $Write_disk1        ; NO error - continue

;
; Error - abort
;
    mov    ds, word ptr cs:S_ds    ; Restore DS
    mov    ah, al
    call    far ptr __maperror    ; Map the error
    jmp    $Write_Error1

; Check for 16K write

$Write_disk1:
    cmp    ax, 04000H
    jnz    $Write_disk2
    ret

$Write_disk2:
    mov    ax,01c1cH        ; Set disk full
    jmp    $Write_error        ; NO - abort

$Write_disk    endp

;
; READ DISK FUNCTION
;
;    BX - file handler
;    SI - Block count
;    DS - Output data segement
;

$Read_disk    proc    near

    mov    ax, 03f00H        ; Set up to read
    mov    cx, 04000H        ; Load count
    xor    dx, dx            ; Clear start address

    int    021H            ; Read the data

    jnc    $Read_OK        ; NO - abort
    jmp    Load_Error        ; Abort - swap file error

;
; Read OK - next block
;

$Read_OK:
    dec    si            ; Decrement block count
    mov    ax, ds            ; Increment offset
    add    ax, 0400H
    mov    ds, ax
    ret

$Read_disk    endp

;
; READ EMS FUNCTION
;
;    BX - file handler
;    SI - Block count - counts from max
;    DS - Output data segement
;

$Read_EMS    proc    near

    call    $map_ems_page        ; Map in the current EMS page
    jnz    Load_Error

    push    ds            ; Save DS and SI
    push    si
    mov    ax, ds
    mov    es, ax
    mov    ds, word ptr cs:_SW_EMSFrame    ; Set Dest Seg
    xor    si, si            ; Clear start
    xor    di, di
    mov    cx, 02000H        ; move 16K
    pushf                ; Save direction flag
    cld
    rep movsw
    popf                ; Restore direction flag
    pop    si            ; And DS, SI
    pop    ds
    jmp    $Read_OK        ; Increment DS and dec SI

$Read_EMS    endp

;
; MAP IN THE CURRENT EMS PAGE
;
;    BX - file handler
;    SI - Block count - counts from max
;    DS - Output data segement
;

$map_ems_page    proc    near

    push    bx            ; Need to save BX
    mov    ax, 04400h        ; Map into physical page zero
    mov    dx, bx            ; Set up handler
    mov    bx, word ptr cs: _SW_Blocks
    sub    bx, si

    int    067H
    pop    bx

    or    ah, ah
    ret

$map_ems_page    endp

;
; DISK SEEK FUNCTION
;
;    BX - file handler
;    DX - offset
;
$Seek_Disk    proc    near

    mov    ax, 04200H        ; Set seek
    xor    cx, cx
    int    021H
    jc    Load_Error        ; Abort - swap file error
    ret

$Seek_Disk    endp

;
; PANIC - Abort
;

Load_Error    proc    near

    mov    di, offset Swap_PANIC
    mov    bx, cs
    mov    ds, bx
    call    I24_Display
$Wait_L:
    sti
    hlt
    jmp    $Wait_L

Load_Error    endp

;
;  WRITE EXTENDED MEMORY
;
;    SI - Block count
;
$Write_extend    proc    near

    push    si            ; Save SI (block counter)
    mov    cx, 02000H        ; Copy a 16K block
    mov    ax, cs            ; Set up GDT address
    mov    es, ax
    mov    si, offset GD_table

    mov    ah, 087H        ; EMS function
    int    015H
    pop    si
    ret

$Write_extend    endp

;
;  READ FROM EXTENDED MEMORY
;
;    SI - Block count
;

$Read_extend    proc    near

    call    $Write_extend
    jc    Load_Error        ; NO - abort

    dec    si            ; Decrement block count

$Read_extend    endp

;
; INCREMENT Extended MEMORY GDT
;
;    AX - used
;
$Inc_Extend    proc    near

    mov    ax, 04000H        ; Increment address by 16K
    add    word ptr cs:GDT_dest_low, ax
    adc    byte ptr cs:GDT_dest_high, 0
    add    word ptr cs:GDT_src_low, ax
    adc    byte ptr cs:GDT_src_high, 0
    ret

$Inc_Extend    endp

;
; LOAD SOURCE GDT ADDRESS
;
;    AX - low order
;    DL - high order
;
$GDT_src_load    proc    near


    mov    word ptr cs:GDT_src_low, ax
    mov    byte ptr cs:GDT_src_high, dl
    ret

$GDT_src_load    endp

;
; LOAD DESTINATION GDT ADDRESS
;
;    AX - low order
;    DL - high order
;
$GDT_dest_load    proc    near

    mov    word ptr cs:GDT_dest_low, ax
    mov    byte ptr cs:GDT_dest_high, dl
    ret

$GDT_dest_load    endp

;
; LOAD the GDT for reloading
;

$GDT_reload    proc    near
    mov    ax, word ptr cs:_SW_EMstart     ; Load Full start address
    mov    dl, byte ptr cs:_SW_EMstart + 2
    call    $GDT_src_load

    mov    ax, word ptr cs:SW_LMstart     ; Load Full start address
    mov    dl, byte ptr cs:SW_LMstart + 2
    call    $GDT_dest_load
    ret
$GDT_reload    endp

;
; CONTROL C INTERRUPT HANDLER - IGNORE
;

SA_IRET        proc    far
    inc    word ptr cs:_SW_intr    ; Set Interrupt 23 detected.
    cmp    byte ptr cs:InShell, 0    ; Are we in the shell ?
    jz    $SA_Ins

; In another program - move the stack around

    stc
    ret


; In shell - ignore interrupt 23 for the moment

$SA_Ins:
    iret

SA_IRET        endp

;
; DIVIDE BY ZERO INTERRUPT HANDLER - Output message
;

SA_DZERO    proc    far

    mov    ax, 00900H
    mov    dx, offset Swap_DZERO
    mov    bx, cs
    mov    ds, bx
    int    021H

    mov    ax, 04CFFh        ; Exit
    int    021H

SA_DZERO    endp

;
; INTERRUPT 24 - ERROR HANDLER - Output message
;
;    AH - Bit  7    = 0 Disk error
;            = 1 FAT error if block device
;                Error code in DI if character device
;      Bit  6    UNUSED
;      Bit  5    = 1 Ignore allowed
;      Bit  4    = 1 Retry allowed
;      Bit  3    = 1 Fail allowed
;      Bits 2 & 1    = Disk Area
;      Bit  0    = 1 Writing error
;    AL         = Disk drive number
;    DI            = Error code
;    BP:SI        = Header of device driver for which error occured
;
;
; Return
;    AL            = 0 Ignore Error
;            = 1 Retry operation
;            = 2 Abort program
;            = 3 Fail system call
;

I24_Errors    equ    $
I24_EC00:    db    'Write protect error$'
I24_EC01:    db    'Unknown unit$'
I24_EC02:    db    'Drive not ready$'
I24_EC03:    db    'Unknown command$'
I24_EC04:    db    'Data error$'
I24_EC05:    db    'Bad request$'
I24_EC06:    db    'Seek error$'
I24_EC07:    db    'Unknown media type$'
I24_EC08:    db    'Sector not found$'
I24_EC09:    db    'Paper out$'
I24_EC0A:    db    'Write fault$'
I24_EC0B:    db    'Read fault$'
I24_EC0C:    db    'General failure$'
I24_EC0D:    db    'Unknown code$'
I24_EC0F:    db    'Invalid disk change$'
I24_EC10:    db    'FCB unavailable$'
I24_EC11:    db    'Sharing buffer overflow$'

;
; Error message address table
;

I24_ECTABLE:    dw    offset I24_EC00
        dw    offset I24_EC01
        dw    offset I24_EC02
        dw    offset I24_EC03
        dw    offset I24_EC04
        dw    offset I24_EC05
        dw    offset I24_EC06
        dw    offset I24_EC07
        dw    offset I24_EC08
        dw    offset I24_EC09
        dw    offset I24_EC0A
        dw    offset I24_EC0B
        dw    offset I24_EC0C
        dw    offset I24_EC0D
        dw    offset I24_EC0D        ; 0E - no message
        dw    offset I24_EC0F
        dw    offset I24_EC10
        dw    offset I24_EC11

I24_ECON:    db    ' when $'
I24_ECREAD:    db    'reading $'
I24_ECWRITE:    db    'writing $'
I24_ECDEVICE:    db    'device $'
I24_ECDISK:    db    'disk $'
I24_EABORT:    db    'Abort$'
I24_EFAIL:    db    ', Fail$'
I24_EIGNORE:    db    ', Ignore$'
I24_ERETRY:    db    ', Retry$'
I24_EDRIVE:    db    '?$'
I24_EQUESTION    db    '? $'
I24_RESPONSE:    db    ' '
I24_ENL:    db    0dH, 0aH, '$'
I24_EBELL:    db    07H, '$'
I24_EDNAME:    db    '12345678$'
I24_EXTECODE:    db    0dH, 0aH, '(Extended Code: '
I24_E_AL:    db    '  '
        db    ' Class: '
I24_E_BH:    db    '  '
        db    ' Action: '
I24_E_BL:    db    '  '
        db    ' Locus: '
I24_E_CH:    db    '  )', 0dH, 0aH, '$'

;
; Save DS, ES, BX, CX, DX
;
_SW_Int24    proc    far
    push    ds        ; Save registers
    push    es
    push    bx
    push    cx
    push    dx

    push    cs        ; Set up data segment
    pop    ds

    mov    cx, ax        ; Save the error information in CX

    push    di
    mov    di, offset I24_ENL
    call    I24_Display
    pop    di

;
;  Check inside message range
;
    cmp    di, 012H
    jb    SWI24a
    mov    di, 0dH

;
; Write the error message
;

SWI24a:
    add    di, di

    mov    di, word ptr ds:I24_ECTABLE[di]
    call    I24_Display

;
; Output on message
;

    mov    di, offset I24_ECON
    call    I24_Display

;
; Output reading or write message
;

    mov    di, offset I24_ECWRITE
    test    ch, 01H
    jnz    SWI24b
    mov    di, offset I24_ECREAD

SWI24b:
    call    I24_Display

;
; Output device message
;

    test    ch, 080H
    jz    SWI24c

    mov    di, offset I24_ECDEVICE
    call    I24_Display

;
; Output device name - up to eight characters
;

    add    si, 0aH            ; Move to device name
    push    ds
    mov    ds, bp
    xor    di, di            ; Set counter

SWI24b1:
    mov    dl, byte ptr ds:[si]    ; Get next character in name
    cmp    dl, ' '
    jz    SWI24d

    mov    byte ptr cs:[I24_EDNAME + di], dl

    inc    si
    inc    di
    cmp    di, 8
    jnz    SWI24b1
;
; Append a $
;

SWI24d:
    pop    ds
    mov    byte ptr cs:[I24_EDNAME + di], '$'
    mov    di, offset I24_EDNAME
    jmp    SWI24e

;
; Write disk error
;
SWI24c:
    mov    di, offset I24_ECDISK
    call    I24_Display

    mov    dl, cl
    add    dl, 'A'
    mov    byte ptr cs:I24_EDRIVE, dl

    mov    di, offset I24_EDRIVE
SWI24e:
    call    I24_Display

;
; Get extended error codes
;
    push    cx
    push    ds
    mov    ah, 059H
    xor    bx, bx
    int    021H

;
; Save responses
;

    mov    byte ptr cs:I24_E_AL, al
    mov    byte ptr cs:I24_E_BL, bl
    mov    byte ptr cs:I24_E_BH, bh
    mov    byte ptr cs:I24_E_CH, ch
    pop    ds
    pop    cx

; Convert to display Hex.

    mov    di, offset I24_E_AL
    call    I24_Convert
    mov    di, offset I24_E_BL
    call    I24_Convert
    mov    di, offset I24_E_BH
    call    I24_Convert
    mov    di, offset I24_E_CH
    call    I24_Convert
    mov    di, offset I24_EXTECODE
    call    I24_Display
;
; Output Options
;
    mov    di, offset I24_EABORT
    call    I24_Display

    test    ch, 020H        ; Ignore allowed ?
    jz    SWI24f
    mov    di, offset I24_EIGNORE
    call    I24_Display

SWI24f:
    test    ch, 010H        ; Retry allowed ?
    jz    SWI24g
    mov    di, offset I24_ERETRY
    call    I24_Display

SWI24g:
    test    ch, 08H            ; Fail allowed ?
    jz    SWI24h
    mov    di, offset I24_EFAIL
    call    I24_Display

;
; Append a question mark.
;

SWI24h:
    mov    di, offset I24_EQUESTION
    call    I24_Display

;
; Get the valid key codes
;
SWI24j:
    xor    ax, ax            ; Read a keyboard character
    int    16H
    and    al, 05fH        ; Upper case

    xor    ah, ah            ; Clear counter
    cmp    al, 'I'            ; Ignore ?
    jnz    SWI24k
    test    ch, 020H
    jnz    SWI24n
SWI24k:
    inc    ah
    cmp    al, 'R'            ; Retry ?
    jnz    SWI24l
    test    ch, 010H
    jnz    SWI24n
SWI24l:
    inc    ah
    cmp    al, 'A'            ; Abort ?
    jz    SWI24n

    inc    ah
    cmp    al, 'F'            ; Fail ?
    jnz    SWI24m
    test    ch, 08H
    jnz    SWI24n
SWI24m:
    mov    di, offset I24_EBELL
    call    I24_Display
    jmp    SWI24j

;
; OK - got code
;
SWI24n:
    mov    cl, ah
    mov    byte ptr ds:I24_RESPONSE, al
    mov    di, offset I24_RESPONSE
    call    I24_Display
    mov    ax, cx

;
; Are we in the shell ?
;
    cmp    byte ptr cs:InShell, 0    ; Are we in the shell ?
    jnz    $SW_int24a        ; No - no processing

    cmp    al, 02H            ; Abort?
    jnz    $SW_int24a        ; No - exit

    test    ah, 008h        ; If fail allowed - convert to fail
    jz    $SW_int24a

    mov    al, 003h        ; Fail system call

$SW_int24a:
    pop    dx            ; Restore registers
    pop    cx
    pop    bx
    pop    es
    pop    ds
    iret
_SW_Int24    endp

;
; Convert Hex code to display code
;
; ds:di Offset of code to replace
; ax is available
;
I24_Convert    proc    near
    push    cx
    mov    al, byte ptr ds:[di]    ; Get the code
    mov    ah, al
    mov    cl, 4
    shr    ah, cl
    and    ah, 0fh

    cmp    ah, 10
    jb    I24_C1
    add    ah, 'A' - 10
    jmp    I24_C2
I24_C1:
    add    ah, '0'
I24_C2:
    mov    byte ptr ds:[di], ah

; Now LSB

    and    al, 0fh
    cmp    al, 10
    jb    I24_C3
    add    al, 'A' - 10
    jmp    I24_C4
I24_C3:
    add    al, '0'
I24_C4:
    mov    byte ptr ds:[di + 1], al
    pop    cx
    ret
I24_Convert    endp
;
;  Display message function for Interrupt 24 processing
;
;  DS:DI message
;  AX is available
;

I24_Display    proc    near
    mov    ah, 08H            ; Get foreground colour
    xor    bx, bx
    int    10H
    mov    bl, ah
    and    bl, 07h

;
; Loop until a $ is hit, outputting the characters
;
I24D:
    mov    al, byte ptr ds:[di]
    cmp    al, '$'
    jnz    I24Da
    ret

I24Da:
    push    di
    mov    ah, 0EH
    int    10H
    pop    di
    inc    di
    jmp    I24D

I24_Display    endp

;
;  Start of overwrite area for environment.  Align on a paragraph
;
;  Also the XMS driver functions used by SH3.C live here
;
        ALIGN    16
Env_OWrite:

;
; XMS INTERFACE
;
; Get Version number.  Return the release number in AX
;

_SW_XMS_Gversion    proc    far

    push    bp            ; Save stack info
    mov    bp, sp

    xor    ax, ax
    call    cs:[_SW_XMS_Driver]

    mov    sp, bp
    pop    bp
    ret

_SW_XMS_Gversion    endp

;
; Allocate N kbytes.  Return the Handler in AX or -1 and error code in
; errno.
;
; Size will be in bp + 6.
;

_SW_XMS_Allocate    proc    far

    push    bp            ; Save stack info
    mov    bp, sp

    mov    dx, word ptr ss:[bp + 6]
    mov    ah, 09H
    call    cs:[_SW_XMS_Driver]
    or    ax, ax
    jnz    $SW_A1

;
; Allocate Failed - return error code
;
    xor    ax, ax
    neg    ax
    xor    bh, bh
    mov    word ptr ds:_errno, bx    ; Save error code
    jmp    $SW_F2

;
; Allocate OK - return handler
;

$SW_A1:
    mov    ax, dx

$SW_A2:
    mov    sp, bp
    pop    bp
    ret

_SW_XMS_Allocate    endp

;
; Release handler.  Return 0 or error code.
;
; Handler will be in bp + 6.
;

_SW_XMS_Free         proc    far

    push    bp            ; Save stack info
    mov    bp, sp

    mov    dx, word ptr ss:[bp + 6]
    mov    ah, 0AH
    call    cs:[_SW_XMS_Driver]
    or    ax, ax
    jnz    $SW_F1
;
; Free Failed - return error code
;
    mov    al, bl
    jmp    $SW_F2

;
; Free OK - return zero
;
$SW_F1:
    xor    ax, ax

$SW_F2:
    mov    sp, bp
    pop    bp
    ret

_SW_XMS_Free         endp
SH0_TEXT    ends
        end