From 468988249754c9196b10cd6f7e29d390f0fdf413 Mon Sep 17 00:00:00 2001
From: Werner Almesberger <werner@almesberger.net>
Date: Mon, 17 Dec 2012 00:45:21 -0300
Subject: [PATCH] swuart/: half-duplex software UART for UBB (WIP)

---
 swuart/Makefile |  19 +++++++++
 swuart/swuart.c | 101 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 120 insertions(+)
 create mode 100644 swuart/Makefile
 create mode 100644 swuart/swuart.c

diff --git a/swuart/Makefile b/swuart/Makefile
new file mode 100644
index 0000000..bd56ff6
--- /dev/null
+++ b/swuart/Makefile
@@ -0,0 +1,19 @@
+CC = mipsel-openwrt-linux-gcc
+CFLAGS = -g -Wall -I../libubb/include
+LDFLAGS = -static
+LDLIBS = -L../libubb -lubb
+
+MAIN = swuart
+OBJS = swuart.o
+
+.PHONY:		all clean spotless
+
+all:		$(MAIN)
+
+$(MAIN):	$(OBJS)
+
+clean:
+		rm -f $(OBJS)
+
+spotless:	clean
+		rm -f $(MAIN)
diff --git a/swuart/swuart.c b/swuart/swuart.c
new file mode 100644
index 0000000..4310be1
--- /dev/null
+++ b/swuart/swuart.c
@@ -0,0 +1,101 @@
+/*
+ * 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);
+}