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/*
* Simple wrapper for writing to a RS232 port. This file is part of the
* DOSMid project.
*
* Copyright (c) 2015, Mateusz Viste
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <conio.h> /* inp() */
#include <dos.h> /* MK_FP() */
#include "rs232.h"
/* get the I/O port for COMx (1..4) */
unsigned short rs232_getport(int x) {
unsigned short far *bioscomtable = MK_FP(0,0x400);
unsigned short res;
if (x < 1) return(0);
if (x > 4) return(0);
res = bioscomtable[x - 1];
return(res);
}
/* check if the COM port is ready for write. loops for some time waiting.
* returns 0 if port seems ready eventually, non-zero otherwise. can be used
* to verify the rs232 presence */
int rs232_check(unsigned short port) {
int i = 4096; /* cycles up to 4K times (should be enough for any UART) */
while (i-- > 0) {
if ((inp(port + 5) & 0x20) != 0) return(0);
}
/* the port wouldn't become ready - exit with error */
return(-1);
}
/* write a byte to the COM port at 'port'. this function will block if the
* UART is not ready to transmit yet. */
void rs232_write(unsigned short port, int data) {
/* wait for the UART to become ready for write */
while ((inp(port + 5) & 0x20) == 0);
/* write the data byte now */
outp(port, data);
}
/* read a byte from COM port at 'port'. returns the read byte, or -1 if
* nothing was available to read. */
int rs232_read(unsigned short port) {
/* if nothing awaits, return -1 */
if ((inp(port + 5) & 0x01) == 0) return(-1);
/* otherwise read from port and return the result */
return(inp(port));
}