/*
 * swuart/swuart.c - Software-implemented half-duplex UART for UBB
 *
 * Written 2012 by Werner Almesberger
 * Copyright 2012 Werner Almesberger
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */


#include <stdlib.h>
#include <unistd.h>

#include <ubb/ubb.h>
#include <ubb/regs4740.h>


#define	TX	UBB_DAT2



static uint32_t tx_mask, rx_mask;
static int loops;


/*
 * TX bit timing:
 *
 * bps		loops	nominal		estimated	measured	error
 * 1152200	 202	  8.696 us	   8.673 us	   8.67 us	-0.3%
 *   38400	 619	 26.042 us	  26.062 us	  26.04 us	n/a
 *    9600	2494	104.167 us	 104.250 us	 104.16 us	n/a
 *
 * Estimated loop timing: 0.25+0.0417*loops
 */

int swuart_open(uint32_t tx, uint32_t rx, int bps)
{
	if (ubb_open(0))
		return -1;

	loops = 24000000/bps-6;
	tx_mask = tx;
	rx_mask = rx;

	ubb_power(1);
	OUT(tx);
	CLR(tx);
	IN(rx);

	return 0;
}


static void send(uint8_t *out, int out_size)
{
	const uint8_t *end = out+out_size;
	unsigned pattern;
	int i, j;

	while (out != end) {
		pattern = 0x200 | (*out++ << 1);
		for (i = 0; i != 10; i++) {
			if (pattern & 1)
				SET(tx_mask);
			else
				CLR(tx_mask);
			pattern >>= 1;
			for (j = 0; j != loops; j++);
		}
	}
}


int swuart_trx(void *out, int out_size, void *in, int in_size, int bit_wait)
{
	uint32_t icmr;

	icmr = ICMR;
	ICMSR = 0xffffffff;

	send(out, out_size);

	ICMCR = ~icmr;

	return 0;
}


int main(int argc, char **argv)
{
	swuart_open(TX, 0, atoi(argv[1]));
	while (1) {
		swuart_trx("U ", 2, NULL, 0, 0);
		usleep(100);
	}
	ubb_close(0);
}