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Assembly Source File | 1993-03-31 | 16.0 KB | 340 lines

;**************************************************************************** ; UMBFILES extends the system file table (SFT) that DOS uses to track ; the state of open files by creating an extension of the SFT in upper ; memory. The syntax is ; ; UMBFILES[=]nn ; ; where "nn" is the number of entries to be created in the SFT extension. ; For best results, boot your system with the statement FILES=8 in CONFIG.- ; SYS, and then allocate room for additional FILES with UMBFILES. For exam- ; ple, if you now boot with the statement FILES=40, change it to FILES=8 and ; add the statement UMBFILES=32 to your CONFIG.SYS file. The sum of FILES ; and UMBFILES may not exceed 255. ; ; NOTE: On some PCs, Windows will not start in 386 enhanced mode unless ; FILES is 10 or 12 or higher. If Windows refuses to start when UMBFILES ; is loaded, increase the FILES setting. ;**************************************************************************** code segment assume cs:code,ds:code org 100h begin: jmp main copyright db "UMBFILES 1.3 Copyright (c) 1993 Jeff Prosise",13,10 db "From: PC Magazine DOS 6 Memory Management " db "with Utilities",13,10,13,10 db "System file table extended",13,10 db "FILES is now equal to $" helpmsg db "Builds an extension to the system file table (SFT) " db "in upper memory.",13,10,13,10 db "UMBFILES[=]nn",13,10,13,10 db " nn Number of new SFT entries to create." db 13,10,13,10 db "UMBFILES requires DOS 5 or DOS 6 and a PC configured " db "to load programs and",13,10 db "device drivers high. The sum of FILES and UMBFILES " db "may not exceed 255.",13,10 crlf db 13,10,"$" errmsg1 db "Requires DOS 5 or DOS 6",13,10,"$" errmsg2 db "Syntax: UMBFILES[=]nn",13,10,"$" errmsg3 db "Invalid parameter or parameter out of range" db 13,10,"$" errmsg4 db "FILES plus UMBFILES may not exceed 255",13,10,"$" errmsg5 db "There is no upper memory available",13,10,"$" errmsg6 db "Insufficient upper memory",13,10,"$" umbfiles dw 0 ;Number of UMBFILES filecount dw 0 ;Resultant number of FILES strategy dw ? ;Memory allocation strategy linkstate dw 0 ;Upper memory link status lastblock dd ? ;Address of final SFT block sftlen dw ? ;Length of SFT extension ;**************************************************************************** ; Procedure MAIN ;**************************************************************************** main proc near cld ;Clear direction flag mov si,81h ;Point SI to command line call scanhelp ;Scan for "/?" switch jnc main1 ;Branch if not found mov ah,09h ;Display help text and exit mov dx,offset helpmsg ;with ERRORLEVEL=0 int 21h mov ax,4C00h int 21h ; ; Check the DOS version and abort if it's not DOS 5 or DOS 6. ; main1: mov ah,30h ;Get DOS version int 21h mov dx,offset errmsg1 ;Load error message address cmp al,5 ;Branch if the major version je main2 ;number is 5 or 6 cmp al,6 je main2 error: mov ah,09h ;Display error message int 21h mov ax,4C01h ;Exit with ERRORLEVEL=1 int 21h ; ; Parse the command line to determine how many SFT entries to create. ; main2: call findchar ;Advance to next character mov dx,offset errmsg2 ;Error if EOL encountered jc error call asc2bin ;Convert ASCII to binary mov dx,offset errmsg3 ;Error if carry is set on jc error ;return or al,al ;Error if number was 0 jz error mov byte ptr umbfiles,al ;Save UMBFILES number ; ; Walk the chain of SFT headers to determine how many FILES already exist. ; xor cx,cx ;Zero SFT entry count mov ah,52h ;Get address of DOS's List int 21h ;of Lists les bx,es:[bx+4] ;Get SFT address in ES:BX main3: mov word ptr lastblock,bx ;Save the header address mov word ptr lastblock[2],es add cx,es:[bx+4] ;Add entries in this block les bx,es:[bx] ;Get address of next block cmp bx,0FFFFh ;Loop if the offset address jne main3 ;is other than FFFFh mov dx,offset errmsg4 ;Verify that FILES plus add cx,umbfiles ;UMBFILES is less than cmp cx,255 ;or equal to 255 and ja error ;abort if it's not mov filecount,cx ;Save new FILES count ; ; Allocate an upper memory block to hold the SFT extension. ; call save_state ;Save the current state mov ax,5803h ;Set the UMB link mov bx,1 int 21h mov dx,offset errmsg5 ;Error if carry set jc error mov ax,5801h ;Change to high-only, best- mov bx,41h ;fit allocation strategy int 21h mov dx,offset errmsg5 ;Error if carry set jc error mov al,59 ;Compute the number of mul byte ptr umbfiles ;paragraphs of memory mov sftlen,ax ;required for the SFT add ax,21 ;extension mov cl,4 shr ax,cl mov bx,ax mov ah,48h ;Request the memory through int 21h ;DOS function 48h jnc main4 ;Branch if call succeeded call restore_state ;Restore the memory state mov dx,offset errmsg6 ;Load error message address jmp error ;Jump to error handler main4: dec ax ;Point ES to MCB preceding mov es,ax ;the memory block mov word ptr es:[01h],ax ;Change owner ID to segment inc word ptr es:[01h] ;address of the UMB mov si,offset copyright ;Copy "UMBFILES" to the MCB mov di,8 ;so that DOS will know mov cx,8 ;who the owner is rep movsb inc ax ;Point ES back to the block mov es,ax ;itself call restore_state ;Restore the memory state ; ; Initialize the new SFT block and link it into the chain. ; mov word ptr es:[00h],0FFFFh ;Initialize the mov word ptr es:[02h],0000h ;SFT header mov ax,umbfiles mov word ptr es:[04h],ax mov cx,sftlen ;Load CX with SFT length xor al,al ;Fill the new SFT with mov di,06h ;zeroes from start to rep stosb ;finish mov ax,es ;Place the address of the les di,lastblock ;new SFT header in what mov word ptr es:[di],00h ;was formerly the final mov word ptr es:[di+2],ax ;SFT block ; ; Display message verifying that the operation is completed, and then exit. ; mov ah,09h ;Display message mov dx,offset copyright int 21h mov ax,filecount ;Display FILES count call bin2asc mov ah,09h ;Next line mov dx,offset crlf int 21h mov ax,4C00h ;Exit with ERRORLEVEL=0 int 21h main endp ;**************************************************************************** ; SAVE_STATE saves the current memory allocation strategy and link state. ;**************************************************************************** save_state proc near mov ax,5800h ;Get the current memory int 21h ;allocation strategy mov strategy,ax ;code and save it mov ax,5802h ;Get the current link int 21h ;status and save it mov byte ptr linkstate,al ret save_state endp ;**************************************************************************** ; RESTORE_STATE restores the memory allocation strategy and link state ; saved earlier. ;**************************************************************************** restore_state proc near mov ax,5801h ;Restore original memory mov bx,strategy ;allocation strategy int 21h mov ax,5803h ;Restore original link mov bx,linkstate ;status int 21h ret restore_state endp ;**************************************************************************** ; SCANHELP scans the command line for a /? switch. If found, carry returns ; set and SI contains its offset. If not found, carry returns clear. ;**************************************************************************** scanhelp proc near push si ;Save SI scanloop: lodsb ;Get a character cmp al,0Dh ;Exit if end of line je scan_exit cmp al,"?" ;Loop if not "?" jne scanloop cmp byte ptr [si-2],"/" ;Loop if not "/" jne scanloop add sp,2 ;Clear the stack sub si,2 ;Adjust SI stc ;Set carry and exit ret scan_exit: pop si ;Restore SI clc ;Clear carry and exit ret scanhelp endp ;**************************************************************************** ; FINDCHAR advances SI to the next non-white-space character. On return, ; carry set indicates EOL was encountered; carry clear indicates it was not. ;**************************************************************************** findchar proc near lodsb ;Get the next character cmp al,09h ;Loop if tab je findchar cmp al,20h ;Loop if space je findchar cmp al,2Ch ;Loop if comma je findchar cmp al,3Dh ;Loop if equal sign je findchar dec si ;Point SI to the character cmp al,0Dh ;Exit with carry set if end je eol ;of line is reached clc ;Clear carry and exit ret eol: stc ;Set carry and exit ret findchar endp ;**************************************************************************** ; ASC2BIN converts a decimal number entered in ASCII form into a binary ; value in AL. Carry set on return indicates that an error occurred in ; the conversion. ;**************************************************************************** asc2bin proc near sub ax,ax ;Initialize registers sub bh,bh mov dl,10 a2b_loop: mov bl,[si] ;Get a character inc si cmp bl,20h ;Exit if space je a2b_exit cmp bl,2Ch ;Exit if comma je a2b_exit cmp bl,0Dh ;Exit if carriage return je a2b_exit cmp bl,"0" ;Error if character is not jb a2b_error ;a number cmp bl,"9" ja a2b_error mul dl ;Multiply the value in AL by jc a2b_error ;10 and exit on overflow sub bl,30h ;ASCII => binary add ax,bx ;Add latest value to AX cmp ax,255 ;Error if sum > 255 jna a2b_loop ;Loop back for more a2b_error: dec si ;Set carry and exit stc ret a2b_exit: dec si ;Clear carry and exit clc ret asc2bin endp ;**************************************************************************** ; BIN2ASC converts a binary value in AX to ASCII form and displays it. ;**************************************************************************** bin2asc proc near mov bx,10 ;Initialize divisor word and xor cx,cx ;digit counter b2a1: inc cx ;Increment digit count xor dx,dx ;Divide by 10 div bx push dx ;Save remainder on stack or ax,ax ;Loop until quotient is zero jnz b2a1 b2a2: pop dx ;Retrieve a digit from stack add dl,30h ;Convert it to ASCII mov ah,2 ;Display it int 21h loop b2a2 ;Loop until done ret bin2asc endp code ends end begin