--- /dev/null
+/*
+ * Copyright © 2012 Keith Packard <keithp@keithp.com>
+ *
+ * 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; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
+ */
+
+#include <ao.h>
+#include <ao_async.h>
+
+#define AO_ASYNC_BAUD 38400l
+#define AO_ASYNC_DELAY (uint8_t) (1000000l / AO_ASYNC_BAUD)
+
+#define LED_PORT PORTB
+
+void
+ao_async_start(void)
+{
+ LED_PORT |= (1 << AO_LED_SERIAL);
+}
+
+void
+ao_async_stop(void)
+{
+ LED_PORT &= ~(1 << AO_LED_SERIAL);
+}
+
+void
+ao_async_byte(uint8_t byte)
+{
+ uint8_t b;
+ uint16_t w;
+
+ /* start data stop */
+ w = (0x000 << 0) | (byte << 1) | (0x001 << 9);
+
+ ao_arch_block_interrupts();
+ for (b = 0; b < 10; b++) {
+ uint8_t v = LED_PORT & ~(1 << AO_LED_SERIAL);
+ v |= (w & 1) << AO_LED_SERIAL;
+ LED_PORT = v;
+ w >>= 1;
+
+ /* Carefully timed to hit around 9600 baud */
+ asm volatile ("nop");
+ asm volatile ("nop");
+
+ asm volatile ("nop");
+ asm volatile ("nop");
+ asm volatile ("nop");
+ asm volatile ("nop");
+ asm volatile ("nop");
+
+ asm volatile ("nop");
+ asm volatile ("nop");
+ asm volatile ("nop");
+ asm volatile ("nop");
+ asm volatile ("nop");
+ }
+ ao_arch_release_interrupts();
+}