rs232.c

/*
 * GZX - George's ZX Spectrum Emulator
 * ZX Spectrum 128K RS-232 port emulation
 *
 * Copyright (c) 1999-2017 Jiri Svoboda
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - 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.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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 <stdio.h>
#include "rs232.h"

void rs232_init(rs232_t *rs, uint32_t d_clocks)
{
	rs->d_clocks = d_clocks;
	rs->state = rs232_idle;
}

void rs232_write(rs232_t *rs, uint8_t val)
{
	uint8_t b;

	/* Spectrum ROM transmits MIDI data via CTS line */
	b = (val >> rs232_cts) & 0x1;

	if (rs->state == rs232_idle && (b == 0x0)) {
		rs->state = rs232_sending;
		rs->bit_no = 0;
		rs->buf = 0x0;
	} else if (rs->state == rs232_sending) {
		rs->buf = (rs->buf >> 1) | (b << 7);
		if (++rs->bit_no >= 8) {
			rs->state = rs232_idle;
			if (rs->sendchar != NULL)
				rs->sendchar(rs->sendchar_arg, rs->buf);
		}
	}
}