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Article 5187 of comp.sys.ibm.pc: Path: cgh!vu-vlsi!cbmvax!rutgers!ames!ucbcad!ucbvax!hoptoad!pozar From: pozar@hoptoad.uucp (Tim Pozar) Newsgroups: comp.lang.c,comp.sys.ibm.pc Subject: Re: C code for opening a communications file Message-ID: <3731@hoptoad.uucp> Date: 25 Dec 87 16:39:42 GMT References: <621@umbc3.UMD.EDU> Reply-To: pozar@hoptoad.UUCP (Tim Pozar) Organization: Syncstream/Widget Systems (San Francisco) Lines: 704 Xref: cgh comp.lang.c:2667 comp.sys.ibm.pc:5187 In article <621@umbc3.UMD.EDU> dipto@umbc3.umd.edu (Dipto Chakravarty) writes: > >Expertise needed to open a communications file (COM1) on an IBM PC !!!!!! > >My fellow C-pals, I need your help to get an equivalent of the following >BASICA code. This code in BASICA works fine as an experiment. However, in >real life, I am required to implement the following in Microsoft C 4.0, >for a communications program. > >100 OPEN "COM1:9600, N, 8, 1, RS, CS, DS, CD" AS #1 > >Above given is the line which opens COM1. The IBM BASIC manual will have >the detailed descriptions of the options used. For my friends who aren't >in touch with the finer details of BASIC syntax here is a short summary >of the options used in the above statement. > >OPEN opens an asynchronous communications file >COM1 communications port 1 >9600 speed; specifying the transmit/receive bit rate in bits/sec (bps) >N specifies that there is no Xmit parity; no receive parity checks >8 specifies the number of transmit/receive data bits >1 specifies the number of stop bits >RS suppreses RTS (Request To Send) >CS this option allows user to ignore this line >DS this option allows user to ignore this line >CD this option allows user to ignore the Carrier Detect checks > Ok, folks here it is. I've been holding off on posting this for more than a year for fear of riticule for the sloppy code. This is an asm source communications functions to be linked in with MSC 3.0 to 5.0. This is only here to see how asm is linked in with MSC and to see how interupt handlers work. If anyone is planning to seriously get into communications routines, I would suggest the FOSSIL drivers, NOT this code. Also look carfully at the code before using it. This is an old version and I think the resettty() is not fully functional... --- /* * Comport.h * * defines the bit masking for the get_mcr() * * Copyright (C) Tim M. Pozar 1987 * */ /* * get_msr() * Function to read (get) the byte located in the Modem Status * Register (3FEh). The table below describes the byte returned. * bit description * 0 Delta Clear to Send (DCTS) * Indicates that the !CTS input to the chip has changed state * since the last time it was read by the processor. * 1 Delta Data Set Ready (DDSR) * Indicates that the !DRS input to the chip has changed since * last time it was read by the processor. * 2 Trailing Edge Ring Indicator (TERI) * Indicates that the !RI input to the chip has changed from * an on (logical 1) to an off (logical 0) condition. * 3 Delta Rx Line Signal detect (DRLSD) * Indicates that the !RLSD input to the chip has changed state. * NOTE: Whenever bit 0, 1, 2, or 3 is set to a logical 1, a modem status * interrupt is generated. * * 4 Clear to Send (CTS) * This bit is the complement of the clear to send (!CTS) input. * If bit 4 (LOOP) of the MCR is set to a logical 1, this is * equivalent to RTS in the MCR. * 5 Data Set Ready (DSR) * This bit is the complement of the data set ready (!DSR) input. * If bit 4 (LOOP) of the MCR is set to a logical 1, this is * equivalent to DTR in the MCR. * 6 Ring Indicator (RI) * This bit is the complement of the ring indicator (!RI) input. * If bit 4 (LOOP) of the MCR is set to a logical 1, this is * equivalent to OUT 1 in the MCR. * 7 Receive Line Signal Detect (RLSD) or Carrier Detect (CD). * This bit is the complement of the received line signal detect * (!RLSD) input. If bit 4 (LOOP) of the MCR is set to a logical 1, * this is equivalent to OUT 2 in the MCR. */ #define DCTS 1 #define DDSR 2 #define TERI 4 #define DRLSD 8 #define CTS 16 #define DST 32 #define RI 64 #define RLSD 128 /* Also know as ... */ #define CD 128 --- ... and the asm code... --- title IBM PC Communications I/O Routines ; ; Orginal code -- Curt Klinsing ; ; Changes and updates -- Copyright (c) 1987 Tim Pozar ; ; ver: 0 ; rev: 2 ; March 13th 1987 ; This code is in a very early stage and should not be let out. ; Several other extensive functions are planned as well as changes ; to the current code. ; ; 2/20/87 ; Changed segment declarations and function names (eg. _function) ; to fit Microsoft C 4.0 and linker requirements. ; ; FUNCTIONS CHANGED/ADDED -- ; set_tty(port_number) ; Function to find current settings of the port and set up serial ; port for 'baud' and 'lcbyte', and enable DTR. This will set up the ; port number base addressed passed to it (eg. 3F8h) and all functions ; will use this port until the function is used again. (NOT READY FOR USE) ; ; reset_tty() ; Function to put the port back into the state it was when it was ; first found by set_tty(). If set_tty() was not called it will not ; change the settings of the port. (NOT READY FOR USE) ; ; 3/13/87 ; get_msr() ; Function to read (get) the byte located in the Modem Status ; Register (3FEh). The table below describes the byte returned. ; bit description ; 0 Delta Clear to Send (DCTS) ; Indicates that the !CTS input to the chip has changed state ; since the last time it was read by the processor. ; 1 Delta Data Set Ready (DDSR) ; Indicates that the !DRS input to the chip has changed since ; last time it was read by the processor. ; 2 Trailing Edge Ring Indicator (TERI) ; Indicates that the !RI input to the chip has changed from ; an on (logical 1) to an off (logical 0) condition. ; 3 Delta Rx Line Signal detect (DRLSD) ; Indicates that the !RLSD input to the chip has changed state. ; NOTE: Whenever bit 0, 1, 2, or 3 is set to a logical 1, a modem status ; interrupt is generated. ; ; 4 Clear to Send (CTS) ; This bit is the complement of the clear to send (!CTS) input. ; If bit 4 (LOOP) of the MCR is set to a logical 1, this is ; equivalent to RTS in the MCR. ; 5 Data Set Ready (DSR) ; This bit is the complement of the data set ready (!DSR) input. ; If bit 4 (LOOP) of the MCR is set to a logical 1, this is ; equivalent to DTR in the MCR. ; 6 Ring Indicator (RI) ; This bit is the complement of the ring indicator (!RI) input. ; If bit 4 (LOOP) of the MCR is set to a logical 1, this is ; equivalent to OUT 1 in the MCR. ; 7 Receive Line Signal Detect (RLSD). ; This bit is the complement of the received line signal detect ; (!RLSD) input. If bit 4 (LOOP) of the MCR is set to a logical 1, ; this is equivalent to OUT 2 in the MCR. ; ; Currently this driver is set up for COM1 (3f8h). ; If you are using the interupt driven buffer, take out the code ; that enables the DTR so that it doesn't get raised until the vectors ; are initilized. ; _TEXT SEGMENT BYTE PUBLIC 'CODE' _TEXT ENDS _DATA SEGMENT BYTE PUBLIC 'DATA' _DATA ENDS CONST SEGMENT BYTE PUBLIC 'CONST' CONST ENDS _BBS SEGMENT BYTE PUBLIC 'BBS' _BBS ENDS DGROUP GROUP CONST, _BBS, _DATA ASSUME CS: _TEXT, DS: DGROUP, SS: DGROUP, ES: DGROUP _TEXT SEGMENT ; ;A set of Lattice C and MSC callable functions to support ;interrupt driven character I/O on the IBM PC. Input ;is buffered, output is polled. ; ;added functions (TMP) -- public _set_tty ;find current settings, and initialize ;comm port to 8 bits and set DTR public _reset_tty ;reset to settings that set_tty() found public _get_msr ;get MSR byte from port. ; ;original functions -- public _init_comm ;initialize the comm port interupts, public _uninit_comm ;remove initialization, public _set_xoff ;enable/disable XON/XOFF, public _get_xoff ;read XON/XOFF state, public _rcvd_xoff ;returns true if XOFF rcvd, public _sent_xoff ;true if XOFF sent, public _inp_cnt ;returns count of rcv chars, public _inp_char ;get one char from buffer, public _inp_flush ;flush input buffer, public _outp_char ;output a character, ; ;A better description can be found in the comment ;block in each function. ; ; assume cs:pgroup ; FALSE EQU 0 TRUE EQU NOT FALSE ; BASE EQU 03F8H ;BASE FOR SERIAL BOARD ; LCR equ BASE+3 ; Line control register IER equ BASE+1 ; Interrup Enable Register MCR EQU BASE+4 ;modem control register MDMSTA EQU BASE+5 ;line status register MDMMSR EQU BASE+6 ;modem status register MDMBAD EQU BASE ;lsb baud resgister EnblDRdy equ 01H ; enable 'data-ready' interrupt bit IntCtlr EQU 21H ;OCW 1 FOR 8259 CONTROLLER EnblIRQ4 EQU 0EFH ;Enable COMMUNICATIONS (IRQ4) dataport EQU BASE ;transmit/receive data port MaskIRQ4 EQU 10H ;BIT TO DISABLE COMM INTERRUPT (IRQ4) MDMCD EQU 80H ;mask for carrier dectect SETBAU EQU 80H ;code for Divisor Latch Access Bit MDMTBE EQU 20H ;8250 tbe flag MDMBRK EQU 40H ;command code for 8250 break LINMOD EQU 03H ;line mode=8 bit, no parity MDMMOD EQU 0BH ;modem mode = DTR and RTS HIGH STOP2 EQU 04H ;BIT FOR TWO STOP BITS IF BAUD<300 RS8259 EQU 20H ;OCW 3 FOR 8259 RSTINT EQU 64H ;SPECIFIC EOI FOR COMM INTERRUPT XOFF EQU 13H ;XOFF character XON EQU 11H ;XON character ; ; MISCELLANEOUS EQUATES ; CR EQU 13 LF EQU 10 DosCall EQU 33 ;INTERRUPT NUMBER FOR DOS CALL CNSTAT EQU 11 ;FUNCTION NUMBER FOR CONSOLE STATUS CNIN EQU 1 ;FUNCTION NUMBER FOR CONSOLE INPUT BUFSIZ EQU 512 ;Max NUMBER OF CHARS SetIntVect EQU 25H ;SET INTERRUPT VECTOR FUNCTION NUMBER ; ; Communication parameters -- ; baud equ 96 ; 1047 = 110 (are you kidding?) ; 384 = 300 ; 96 = 1200 ; 48 = 2400 ; 24 = 4800 ; 12 = 9600 parity equ 00000b ;00000 = none ;01000 = odd ;11000 = even stopbit equ 000b ; 000 = 1 bit ; 100 = 2 bits wordlth equ 11b ; 10 = 7 bits ; 11 = 8 bits lcbyte equ parity+stopbit+wordlth ;line control byte div_on equ 80h ;divisor latch access bit (DLAB) ; ; DUMP BUFFER, COUNT AND POINTER. ; CIRC_BUF DB BUFSIZ DUP(?) ;ALLOW 512 MaxIMUM BUFFERED CHARACTERS BUF_TOP EQU $ - 1 ;KEEP TRACK OF THE TOP OF THE BUFFER CIRC_TOP DW BUF_TOP ; ; CIRC_IN DW OFFSET CIRC_BUF ;POINTER TO LAST CHAR. PLACED IN BUFFER CIRC_CUR DW OFFSET CIRC_BUF ;POINTER TO NEXT CHAR. TO BE RETRIEVED FROM ; BUFFER CIRC_CT DW 0 ;COUNT OF CHARACTERS USED IN BUFFER SNT_XOFF DB FALSE ;FLAG TO CHECK IF AN XOFF HAS BEEN SEND GOT_XOFF DB FALSE ;FLAG TO CHECK IF AN XOFF HAS BEEN RECEIVED SEE_XOFF DB FALSE ;FLAT TO SEE IF WE ARE INTERESTED IN XON/XOFF ; ; ; set_tty() ; _set_tty proc near push bp ; mov dx,mcr ; in al,dx ; get modem parameters ; mov MCR_BYTE,al ; save them mov dx,lcr ; in al,dx ; get line parameters ; mov LCR_BYTE,al ; save them mov al,div_on out dx,al ; set 8250 for baud rate selection ; can the baud rate divisor be read to save the settings? ; if so, stick the code here. mov ax,baud mov dx,mdmbad out dx,al ; low byte divisor mov al,ah inc dx out dx,al ; high byte divisor mov dx,lcr mov al,lcbyte out dx,al ; set line control reg. mov dx,mcr in al,dx or al,mdmmod out dx,al ; set DTR high flsh: mov dx,dataport in al,dx mov dx,mdmsta in al,dx and al,1 jnz flsh pop bp ret _set_tty endp _reset_tty proc near push bp pop bp ret _reset_tty endp _get_msr proc near push bp push ds ; save data segment push cs pop ds xor ax,ax mov dx,MDMMSR in al,dx pop ds pop bp ret _get_msr endp ; ; set_xoff(flag) Enable (flag != 0) or disable ;int flag; (flag == 0) XON/ XOFF protocol ; for the character input stream. ;If enabled, an XOFF will be sent when the buffer ;reaches 3/4 full. NOTE: an XON will not be sent auto- ;matically. Your program must do it when it sees ;the _rcvd_xoff() flag, and ready for more chars. ; _set_xoff proc near push bp PUSH DS ;SAVE DATA SEGMENT mov bx,[bp+6] push cs pop ds ; move code seg addr to data seg reg. cmp bx,0 jnz to_on mov see_xoff,FALSE jmp done1 to_on: mov see_xoff,TRUE done1: pop ds pop bp ret _set_xoff endp ; ;flag = get_xoff() Returns the current setting ; of the XON/ XOFF flag set ;by set_xoff(), above. ; _get_xoff proc near push bp push ds ; save data reg push cs pop ds ; move code seg addr to data seg reg. xor ax,ax mov al,see_xoff pop ds pop bp ret _get_xoff endp ; ;flag = sent_xoff(); Returns true if an XOFF ; character was sent, indicating ;the receive buffer is 3/4 full. ; _sent_xoff proc near push bp push ds ; save data reg push cs pop ds ; move code seg addr to data seg reg. xor ax,ax mov al,snt_xoff pop ds pop bp ret _sent_xoff endp ; ; rcvd_xoff() Returns true if an XOFF was ; received; will return false as ;soon as an XON is received. Does not effect data output, ;only indicates the above. (Obviously useless for binary ;data.) ; _rcvd_xoff proc near push bp push ds ; save data reg push cs pop ds ; move code seg addr to data seg reg. xor ax,ax mov al,got_xoff pop ds ; restore data reg pop bp ret _rcvd_xoff endp ; ;count = inp_cnt() Returns the number of characters ; available in the input buffer. ; _inp_cnt proc near push bp push ds ; save data segment push cs pop ds ; move code seg addr to data seg reg mov ax,circ_ct pop ds pop bp ret _inp_cnt endp ; ; inp_flush() Flush the input buffer. ; _inp_flush proc near push bp push ds ; save data reg push cs pop ds ; move code seg addr to data seg reg. mov bx,offset circ_buf mov circ_in,bx mov circ_cur,bx xor ax,ax mov circ_ct,ax pop ds pop bp ret _inp_flush endp ; --------- Init ----------------------------------- ; Program initialization: ; -- Set up vector for RS232 interrupt (0CH) ; -- Enbl IRQ4 ; -- Enbl RS232 interrupt on data ready ; ; --------------------------------------------------- _init_comm proc near push bp cli ; ---- Set up INT x'0C' for IRQ4 push ds push cs pop ds ;cs to ds mov dx,offset IntHdlr ;relative adddres of interrupt handler mov al,0cH ;interrupt number for comm. mov ah,SetIntVect ;function number for setting int vector int DosCall ;set interrupt in 8086 table pop ds ;restore DS ; ---- Enbl IRQ4 on 8259 interrupt controller cli in al,IntCtlr ; get current masks and al,EnblIRQ4 ; Reset IRQ4 mask out IntCtlr,al ; And restore to IMR ; --- Enbl 8250 data ready interrupt mov dx,LCR ; DX ==> LCR in al,dx ; Reset DLAB for IER access and al,7FH out dx,al mov dx,IER ; Interrupt Enbl Register mov al,EnblDRdy ; Enable 'data-ready' interrupt out dx,al ; --- Enbl OUT2 on 8250 mov dx,MCR ; modem control register in al,dx ; Enable OUT2 or al,08h ; find out what is in there and out dx,al ; enable the DTR sti pop bp ret _init_comm endp ; ; uninit_comm() Removes the interrupt structure ; installed by _init_comm(). Must be ;done before passing control to the DOS, else chars received ;will be stored into the next program loaded! ; _uninit_comm proc near push bp ; --- Disable IRQ4 on 8259 cli in al,IntCtlr ;GET OCW1 FROM 8259 or al,MaskIRQ4 ;DISABLE COMMUNICATIONS INTERRUPT out IntCtlr,al ; --- Disable 8250 data ready interrupt mov dx,LCR ; DX ==> LCR in al,dx ; Reset DLAB for IER access and al,7FH out dx,al mov dx,IER ; Interrupt Enbl Register mov al,0 ; Disable all 8250 interrupts out dx,al ; --- Disable OUT2 on 8250 mov dx,MCR ; modem control register mov al,0 ; Disable OUT2 out dx,al sti pop bp ret _uninit_comm endp ; ;char inp_char() Return a character from the input ; buffer. Assumes you have called ;inp_cnt() to see if theres any characters to get. ; _inp_char proc near push bp push ds ; save data reg push cs pop ds ; move code seg addr to data seg reg. mov bx,circ_cur xor ax,ax mov al,[bx] ;get next char from circ_buf DEC circ_ct ;decrement circ_buf COUNT CMP bx,circ_top ;ARE WE AT THE TOP OF THE circ_buf? JZ reset_cur ;JUMP IF SO INC bx ;ELSE, BUMP PTR JMP SHORT upd_cur reset_cur: mov bx,OFFSET circ_buf ;RESET circ_in TO BOTTOM OF BUF. upd_cur: mov circ_cur,bx ;SAVE NEW PTR xor cx,cx mov cl,see_xoff ;check if interested in xon/xoff cmp cl,TRUE jnz clnup2 ;not interested, so goto return cmp snt_xoff,TRUE ;have we sent an xoff? jnz clnup2 ;no, so return cmp circ_ct,80h ;yes, so see in buf is now emptying jg clnup2 ;not empty enuf to send xon, jump to ret mov snt_xoff,FALSE mov cl,XON push ax ; save char call comout pop ax clnup2: pop DS ;GET BACK ENTERING DS pop bp ret _inp_char endp ; ; outp_char(c) Output the character to the ;char c; serial port. This is not buffered ; or interrupt driven. ; _outp_char proc near push bp mov bp,sp mov cl,[bp+4] sti call comout pop bp ret _outp_char endp ; ;Local subroutine: output CL to the port. ; comout: mov dx,MDMSTA in al,dx ; get 8250 status and al,MDMTBE ; check for transmitter ready jz comout ; jump if not to wait mov al,cl ; get char to al mov dx,dataport out dx,al ; output char to 8251 ret ; ; RECEIVE INTERRUPT HANDLER (CHANGED TO PLACE CHARACTERS IN A ; CIRCULAR circ_buf AND TO SEND AN XOFF IF THE circ_buf IS MORE THAN ; 3/4 FULL - S.G.) ; IntHdlr: CLI push cx push dx push bx push ax push ds mov ax,cs ;get cur code segment mov ds,ax ;and set it as data segment mov bx,circ_in ;GET circ_buf IN PTR mov DX,dataport ;GET DATA PORT NUMBER IN AL,DX ;GET RECEIVED CHARACTER ; push ax ; push dx ; xor ax,ax ; xor dx,dx ; mov dl,al ; mov ah,2 ; int DosCall ; pop dx ; pop ax xor cx,cx mov cl,see_xoff ;check if interested in xon/xoff cmp cl,TRUE jnz ck_full ;not interested goto ck if buf full mov cl,al ;put char in cl for testing and cl,7fh ;turn off any parity bits cmp cl,XOFF ;see if we got an xoff jnz ck_xon mov got_Xoff,TRUE ; code for handling xon/xoff from remote jmp clnup ck_xon: cmp cl,XON jnz reg_ch mov got_Xoff,FALSE jmp clnup ; ;Normal character; not XON/XOFF, or XON/XOFF disabled. ; reg_ch: test snt_Xoff,TRUE ;SEE IF sentXoff IS SET jnz ck_full ;IF SO, DON'T SEND ANOTHER XOFF CMP circ_ct,(BUFSIZ * 3)/4 ;ALLOW BUF TO BECOME 3/4 FULL BEFORE ; SENDING XOFF jb savch ;IF IT'S OK, CONTINUE push ax ;SAVE CHARACTER mov CL,XOFF ;GET XOFF CHARACTER mov snt_Xoff,TRUE ;RESET sentXoff call comout ; AND SEND IT pop ax ;RETRIEVE CHARACTER JMP SHORT savch ;IF WE'RE HERE, THE circ_buf HAS BUFSIZ-80H ; CHARACTERS ck_full: CMP circ_ct,BUFSIZ ;SEE IF circ_buf ALREADY FULL JZ clnup ; JUMP IF SO, DO NOT PLACE CHARACTER IN BFR savch: mov [bx],AL ;SAVE NEW CHARACTER IN circ_buf inc circ_ct ;BUMP circ_buf COUNT CMP bx,circ_top ;ARE WE AT THE TOP OF THE circ_buf? JZ reset_in ;JUMP IF SO inc bx ;ELSE, BUMP PTR JMP SHORT into_buf reset_in: mov bx,OFFSET circ_buf ;RESET circ_in TO BOTTOM OF BUF. into_buf: mov circ_in,bx ;SAVE NEW PTR clnup: mov AL,RSTINT OUT RS8259,AL ;ISSUE SPECIFIC EOI FOR 8259 pop ds ;GET BACK ENTERING DS pop ax pop bx pop dx pop cx sti iret _TEXT ENDS end --- And that's all folks!!! -- ======================================================================= | ...sun!hoptoad!\ Tim Pozar | | >fidogate!pozar Fido: 1:125/406 | | ...lll-winken!/ PaBell: (415) 788-3904 | | USNail: KKSF 77 Maiden Lane San Francisco CA 94108 | =======================================================================