COMMENT * CLUBware (tm) BASPRINT - Enhancement to the Basic Interpreter Print statement Copyright 1984 Rayhawk Automation N.W. Inc P.O. Box 1427 Beaverton, Oregon 97075 * SCRDSEG SEGMENT ASSUME CS:SCRDSEG,DS:NOTHING,ES:NOTHING,SS:STACK ORIG_INT10 LABEL WORD ; original int 10 DW 0 DW 0 ;______________________________________________________________________________ ; Swap the B4 interrupt used by BASIC to print strings. Swap must be made ; after BASIC has been loaded and initialized its environment. Swap takes ; place when BASIC clears the screen. ORIG_INTB4 LABEL WORD ; original int b4 DW 0 DW 0 INTSWAP PROC FAR CMP AX,0600h ; clear screen request? JE DO_SWAP JMP DWORD PTR ORIG_INT10 ; pass call to BIOS DO_SWAP: PUSH DS PUSH AX SUB AX,AX ; address low memory MOV DS,AX CLI ; disable interrupts for a moment ; vector for B4 is at 2D0 ; have we already taken over this interrupt once before? CMP WORD PTR DS:[02D0h],OFFSET PRINTER JE ALREADY_SAVED ; save the original interrupt vector for use by error message reports MOV AX,WORD PTR DS:[02D0h] MOV ORIG_INTB4,AX MOV AX,WORD PTR DS:[02D2h] MOV ORIG_INTB4+2,AX ; replace the original interrupt vector to allow us to intercept prints MOV AX,OFFSET PRINTER MOV WORD PTR DS:[02D0h],AX MOV AX,SEG PRINTER MOV WORD PTR DS:[02D2h],AX ALREADY_SAVED: STI POP AX POP DS JMP DWORD PTR ORIG_INT10 ; pass clear screen to BIOS now INTSWAP ENDP ;______________________________________________________________________________ COMMENT * PRINTER prints a character string on the screen starting at the current cursor position. After the string is written to the screen the cursor position is updated to just after the string. To use this routine, INTSWAP must have swapped the interrupt vector for intterupt B4 and redirected it to the PRINTER subroutine. The BASPRINT module will take over the INT 10h and make this module permanently resident. When the screen is cleared by BASIC, INTSWAP will swap INT B4 and point the vector to the PRINTER subroutine. Algorithm: check context for simple text to screen or possibly something more involved that basic should handle 1) store character count and mark the flag for type of i/o 2) load current page from DS:[0049] 3) load current position on page from DS:[0056] 4) load attribute for string from DS:[004E] 5) move character count to CX for use in loop 6) load type of crt display from 0000:463 7) address the screen segment 8) move string to screen while synchronizing with horizontal retrace 9) update cursor position on screen 10) update cursor position in database at DS:[0056] 11) leave registers in manner BASIC expects On entry DS:[SI] points to string to write DH contains count of characters to write DS:[CX] also points to string and must be updated on exit DS:[0049] contains the page to which we write DS:[004E] contains the attribute for the text DS:[0056] contains the current screen location and must be updated after print is complete * ;______________________________________________________________________________ ; Local data addressable through CS register CHAR_COUNT LABEL BYTE DB 0 LINE_START LABEL WORD DW 0 ; 0 DW 160 ; 1 DW 320 ; 2 DW 480 ; 3 DW 640 ; 4 DW 800 ; 5 DW 960 ; 6 DW 1120 ; 7 DW 1280 ; 8 DW 1440 ; 9 DW 1600 ; 10 DW 1760 ; 11 DW 1920 ; 12 DW 2080 ; 13 DW 2240 ; 14 DW 2400 ; 15 DW 2560 ; 16 DW 2720 ; 17 DW 2880 ; 18 DW 3040 ; 19 DW 3200 ; 20 DW 3360 ; 21 DW 3520 ; 22 DW 3680 ; 23 DW 3840 ; 24 PAGE_START LABEL WORD DW 0 DW 4000 DW 8000 DW 12000 STARTING_PAGE LABEL WORD DW 0 END_OF_PAGE LABEL WORD DW 0 STARTING_LINE LABEL WORD DW 0 RESIDUAL LABEL BYTE DB 0 ROM_SEGMENT LABEL WORD ; basic segment in ROM DW 0F600h LOCAL_FLAG LABEL BYTE DB 00000000b JUST_BLANKS EQU 00000001b ; basic wants just blanks displayed ;______________________________________________________________________________ COMMENT * New service routine for interrupt B4 Calls to routine F600:2BA5 generate B4 interrupts. These calls come from several places within the BASIC ROM. We service calls from two locations: 26CC - call to display a string 148D - call to display blanks Calls from anywhere else are serviced by the original basic code. The two labels corresponding to the two types of calls we service are STRING_IO REPEAT_BLANKS The code labeled BASIC_IO passes the interrupt back to the basic code for service. * PRINTER PROC FAR PUSH BP MOV BP,SP ; address the stack ; check context for simple text to screen or possibly something ; more involved that basic should handle CMP WORD PTR DS:[04E9h],0 JNE BASIC_IO CMP WORD PTR DS:[071Fh],0 JNE BASIC_IO CMP BYTE PTR DS:[0758h],0 JNE BASIC_IO CMP BYTE PTR DS:[071Bh],0 JNE BASIC_IO CMP BYTE PTR DS:[0029h],50h ; 80 bytes per line? JNE BASIC_IO CMP BYTE PTR DS:[0056h],25 ; on bottom line of screen? JE BASIC_IO ; if so, let basic handle it CMP WORD PTR [BP+8],26CCh ; just regular i/o? JE STRING_IO CMP WORD PTR [BP+8],148Dh ; just repeated blanks? JE REPEAT_BLANKS ; allow original B4 service routine to perform I/O BASIC_IO: POP BP JMP DWORD PTR ORIG_INTB4 ; pass control to original B4 ; ---------- ; repeated blanks sent to screen REPEAT_BLANKS: PUSH BX ; save registers used PUSH DX PUSH DI PUSH ES PUSH CX ; ... 1) store character count and mark the flag for type of i/o MOV CHAR_COUNT,CH ; save character count OR LOCAL_FLAG,JUST_BLANKS MOV RESIDUAL,DH ; dh should be untouched JMP SETUP_START ; ---------- ; write the string for basic STRING_IO: PUSH BX ; save registers used, PUSH DX PUSH DI PUSH ES ; ... 1) backup to start of string and store character count DEC SI ; backup to start of string MOV CHAR_COUNT,DH ; save character count MOV LOCAL_FLAG,0 ; clear the flag for string i/o MOV RESIDUAL,1 ; dh to contain 1 on exit ; ... 2) load current page from DS:[0049] SETUP_START: MOV BL,BYTE PTR DS:[0049h] ; load current page SUB BH,BH SHL BX,1 ; convert to a table offset MOV DI,PAGE_START[BX] ; load start of page MOV STARTING_PAGE,DI ; save the page MOV END_OF_PAGE,DI ; save ending page pointer ADD END_OF_PAGE,3840 ; ... 3) load current position on page from DS:[0056] MOV DX,WORD PTR DS:[0056h] ; load current position DEC DH ; basic counts from 1 instead of 0 DEC DL ; basic counts from 1 instead of 0 MOV BL,DL ; load row number SHL BX,1 ; two bytes per table entry ADD DI,LINE_START[BX] ; add in start of line MOV STARTING_LINE,DI ; store this for later MOV DL,DH ; bring down column number SUB DH,DH ADD DI,DX ; add in column position ADD DI,DX ; account for attribute bytes ; ... 4) load attribute for string from DS:[004E] MOV BH,BYTE PTR DS:[004Eh] ; load attribute for string ; ... 5) move character count to CX for use in loop SUB CH,CH ; clear upper byte MOV CL,CHAR_COUNT ; load the character count ; ... 6) load type of crt display from 0000:463 SUB AX,AX ; address system memory MOV ES,AX MOV DX,WORD PTR ES:[463h] ; load address of display adapter ADD DX,6 ; address crt status port ; ... 7) address the screen segment MOV AX,0B000h ; screen seg for monochrome card CMP DX,03DAh ; is this a graphic card? JNE MONOCHROME MOV AX,0B800h ; load screen seg for graphic card MONOCHROME: MOV ES,AX ; address the screen buffer ; ... 8) move string to screen while synchronizing ; with horizontal retrace TEST LOCAL_FLAG,JUST_BLANKS JZ DISPLAY_LOOP MOV BL,20h ; load a blank BLANK_LOOP: CALL DISPLAY_CHAR ; display a line of blanks for basic LOOP BLANK_LOOP JMP UPDATE_POSITION DISPLAY_LOOP: LODSB ; load next character CMP AL,20h ; special character? JGE NOT_SPECIAL CALL SPECIAL JZ ANOTHER_CHAR ; if flag set, go for another character NOT_SPECIAL: MOV BL,AL CLI HSYNC_WAIT1: IN AL,DX ; check for horizontal retrace TEST AL,1 JNZ HSYNC_WAIT1 ; wait for retrace HSYNC_WAIT2: IN AL,DX ; check for horizontal retrace TEST AL,1 JZ HSYNC_WAIT2 ; wait for retrace MOV AX,BX STOSW ; store character and attribute ANOTHER_CHAR: STI CMP DI,END_OF_PAGE JL NOT_SCROLLED MOV AL,0Dh ; force a carriage return CALL SPECIAL NOT_SCROLLED: LOOP DISPLAY_LOOP ; repeat cx times ; ... 9) update cursor position on screen UPDATE_POSITION: MOV AX,DI SUB AX,STARTING_PAGE SHR AX,1 ; eliminate attribute bytes SUB DX,DX MOV BX,80 ; divide by bytes per line DIV BX ; quotient in AL (ROW) ; remainder in DL (COLUMN) MOV DH,AL MOV BH,BYTE PTR DS:[0049h] ; load page number MOV AH,2 ; request new position INT 10h ; ... 10) update cursor position in database at DS:[0056] XCHG DH,DL ; basic likes this reversed INC DH ; basic counts from 1 instead of 0 INC DL ; basic counts from 1 instead of 0 MOV WORD PTR DS:[0056h],DX ; ... 11) leave registers in manner BASIC expects TEST LOCAL_FLAG,JUST_BLANKS JZ STRING_DISPLAYED POP CX ; restore original blank count MOV CH,1 ; allow basic to decrement this to 0 JMP RESTORE_REGS STRING_DISPLAYED: ; for a string MOV CX,SI ; CX must point to last character DEC CX RESTORE_REGS: POP ES POP DI POP DX MOV DH,RESIDUAL ; let decrement instr take this to zero ; inside basic interpreter POP BX POP BP ADD SP,4 ; throw away offset and code segment ; from INT B4 POPF ; restore flags from interrupt POP AX ; throw away near call on stack PUSH ROM_SEGMENT ; and convert to a far call PUSH AX MOV AL,20h ; leave a character in AL for basic ; to compare against a CR (0Dh) RET ; return to ROM PRINTER ENDP ;______________________________________________________________________________ ; subroutine to handle special control characters SPECIAL PROC NEAR ; ---------- CMP AL,0Ah ; line feed? JE NEW_LINE ; ---------- CMP AL,0Bh ; home? JNE NOT_HOME MOV DI,STARTING_PAGE ; start over at top of screen MOV STARTING_LINE,DI SUB AL,AL RET NOT_HOME: ; ---------- CMP AL,0Ch ; clear screen? JNE NOT_CLEAR MOV DI,STARTING_PAGE MOV STARTING_LINE,DI MOV AL,0 ; clear whole window JMP SHORT SCROLL_SCREEN NOT_CLEAR: ; ---------- CMP AL,0Dh ; carriage return? JNE NOT_CR NEW_LINE: MOV DI,STARTING_LINE ADD DI,160 JMP SHORT TEST_RIGHT NOT_CR: ; ---------- CMP AL,1Ch ; move right? JNE NOT_RIGHT ADD DI,2 JMP SHORT TEST_RIGHT NOT_RIGHT: ; ---------- CMP AL,1Dh ; move left? JNE NOT_LEFT SUB DI,2 JMP SHORT TEST_LEFT NOT_LEFT: ; ---------- CMP AL,1Eh ; move up? JNE NOT_UP SUB DI,160 JMP SHORT TEST_LEFT NOT_UP: ; ---------- CMP AL,1Fh ; move down? JNE NOT_DOWN ADD DI,160 JMP SHORT TEST_RIGHT NOT_DOWN: JMP SHORT TEST_FOR_TAB ; ---------- TEST_RIGHT: MOV AX,DI ; are we past line 24? SUB AX,STARTING_PAGE CMP AX,3840 JL VALID_RIGHT MOV DI,STARTING_PAGE ; back at start of last line ADD DI,3680 MOV STARTING_LINE,DI MOV AL,1 ; scroll one line JMP SHORT SCROLL_SCREEN VALID_RIGHT: SUB AL,AL RET ; ---------- SCROLL_SCREEN: PUSH CX MOV CX,0 ; start in upper left corner PUSH DX MOV DX,174Fh ; end in lower right, one line up MOV AH,6 PUSHF ; simulate an INT 10 CALL DWORD PTR ORIG_INT10 POP DX POP CX SUB AL,AL RET ; ---------- TEST_LEFT: CMP DI,STARTING_PAGE JGE VALID_LEFT MOV DI,STARTING_PAGE VALID_LEFT: SUB AL,AL RET ; ---------- TEST_FOR_TAB: CMP AL,09h ; tab? JNE NOT_TAB PUSH CX PUSH DX MOV AX,DI SUB AX,STARTING_LINE SHR AX,1 ; discount attribute bytes SUB DX,DX MOV CX,8 DIV CX MOV CX,8 ; tab positions are every 8 charactes SUB CX,DX ; subtract off remainder MOV BL,' ' ; write some blanks POP DX TAB_LOOP: CALL DISPLAY_CHAR LOOP TAB_LOOP POP CX SUB AL,AL RET NOT_TAB: ; ---------- CMP AL,08h ; backspace? JNE NOT_BACKSPACE CMP DI,STARTING_LINE JE AT_START SUB DI,2 ; back up a space AT_START: MOV BL,' ' ; write a blank CALL DISPLAY_CHAR SUB DI,2 ; back up a space SUB AL,AL RET NOT_BACKSPACE: ; ---------- MOV AH,2 SUB AH,1 ; set flag to display the char RET SPECIAL ENDP ;______________________________________________________________________________ ; routine to display a character in BL - used only for special characters ; attribute is in BH DISPLAY_CHAR PROC NEAR CLI HSYNC_WAIT3: IN AL,DX ; check for horizontal retrace TEST AL,1 JNZ HSYNC_WAIT3 ; wait for retrace HSYNC_WAIT4: IN AL,DX ; check for horizontal retrace TEST AL,1 JZ HSYNC_WAIT4 ; wait for retrace MOV AX,BX STOSW ; store character and attribute STI RET DISPLAY_CHAR ENDP ;______________________________________________________________________________ LASTADDR LABEL BYTE COPYRIGHT LABEL BYTE DB 10,13 DB ' CLUBware (tm)',10,13,10,13 DB 'BASPRINT - Enhancement to the Basic Interpreter Print statement' DB 10,13,10,13 DB ' Copyright 1984 Rayhawk Automation N.W. Inc',10,13 DB ' P.O. Box 1427',10,13 DB ' Beaverton, Oregon 97075',10,13,'$' ;______________________________________________________________________________ BASPRINT PROC FAR PUSH DS ; Push addr of Program Segment Prefix SUB AX,AX ; Zero AX PUSH AX ; Push zero onto stack ; (offset of INT 20 within PSP) ; | - - - - - - - - - - - - - - - - - - - - - - - - -| ; | | ; | take over the INT 10h | ; | interrupt if not already done | ; | | ; | - - - - - - - - - - - - - - - - - - - - - - - - -| MOV DS,AX ; address low memory LDS BX,DWORD PTR DS:[02D0h] ; load interrupt vector for int B4 MOV AX,WORD PTR PRINTER CMP AX,WORD PTR DS:[BX] JNE NOT_HERE_YET MOV AX,WORD PTR PRINTER+2 CMP AX,WORD PTR DS:[BX+2] JNE NOT_HERE_YET MOV AX,WORD PTR PRINTER+4 CMP AX,WORD PTR DS:[BX+4] JNE NOT_HERE_YET MOV AX,WORD PTR PRINTER+6 CMP AX,WORD PTR DS:[BX+6] JNE NOT_HERE_YET JMP ALREADY_RESIDENT NOT_HERE_YET: SUB AX,AX MOV DS,AX MOV AX,WORD PTR DS:[40h] ; save original int10 MOV ORIG_INT10,AX MOV AX,WORD PTR DS:[42h] MOV ORIG_INT10+2,AX MOV AX,SEG BASPRINT MOV DS,AX MOV DX,OFFSET INTSWAP ; Load offset of interrupt service mod MOV AX,2510h ; Prepare for DOS service call type 25 ; to establish service for INT 10 INT 21h ; Ask DOS to establish service ; | - - - - - - - - - - - - - - - - - - - - - - - - -| ; | | ; | issue copyright message | ; | | ; | - - - - - - - - - - - - - - - - - - - - - - - - -| MOV DX,OFFSET COPYRIGHT MOV AH,9 INT 21h ; | - - - - - - - - - - - - - - - - - - - - - - - - -| ; | | ; | modify INT 20 into INT 27 in the | ; | program segment prefix | ; | | ; | - - - - - - - - - - - - - - - - - - - - - - - - -| MOV BYTE PTR ES:[01],27h ; Change INT 20h to INT 27h ; | - - - - - - - - - - - - - - - - - - - - - - - - -| ; | | ; | 6) load address of ending tag into DX | ; | | ; | - - - - - - - - - - - - - - - - - - - - - - - - -| MOV AX,SEG LASTADDR SUB AX,SEG BASPRINT MOV CL,4 ; prepare for 4 bit shift SHL AX,CL ; shift up (convert from seg to abs) ADD AX,OFFSET LASTADDR ; add address of bottom location ADD AX,0103h ; Pad offset because DOS measures ; offset relative to Program ; Segment Prefix MOV DX,AX ; leave where DOS will find it ; | - - - - - - - - - - - - - - - - - - - - - - - - -| ; | | ; | 7) use RET FAR to return to DOS and | ; | leave service routine resident | ; | | ; | - - - - - - - - - - - - - - - - - - - - - - - - -| ALREADY_RESIDENT: RET BASPRINT ENDP SCRDSEG ENDS ;______________________________________________________________________________ STACK SEGMENT PARA STACK 'STACK' DB 24 DUP('STACK***') TOPSTACK DB 0 STACK ENDS END BASPRINT