1 files changed, 115 insertions, 0 deletions
diff --git a/src/avr/ao_spi_slave.c b/src/avr/ao_spi_slave.c
new file mode 100644
index 00000000..b742d29a
--- /dev/null
+++ b/src/avr/ao_spi_slave.c
@@ -0,0 +1,115 @@
+/*
+ * Copyright © 2011 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"
+
+uint8_t
+ao_spi_slave_recv(uint8_t *buf, uint8_t len)
+{
+	while (len--) {
+		while (!(SPSR & (1 << SPIF)))
+			if ((PINB & (1 << PINB0)))
+				return 0;
+		*buf++ = SPDR;
+	}
+	return 1;
+}
+
+void
+ao_spi_slave_send(uint8_t *buf, uint8_t len)
+{
+	while (len--) {
+		SPDR = *buf++;
+		while (!(SPSR & (1 << SPIF)))
+			if ((PINB & (1 << PINB0)))
+				return;
+	}
+	/* Clear pending SPIF bit by reading */
+	(void) SPDR;
+}
+
+static uint8_t ao_spi_slave_running;
+
+ISR(PCINT0_vect)
+{
+	cli();
+#if SPI_SLAVE_PIN_0_3
+	if ((PINB & (1 << PORTB0)) == 0)
+#endif
+#if SPI_SLAVE_PIN_2_5
+	if ((PINB & (1 << PORTB2)) == 0)
+#endif
+	{
+		if (!ao_spi_slave_running) {
+			ao_spi_slave_running = 1;
+			ao_spi_slave();
+		}
+	} else {
+		ao_spi_slave_running = 0;
+	}
+	sei();
+}
+
+void
+ao_spi_slave_init(void)
+{
+	/* We'd like to have a pull-up on SS so that disconnecting the
+	 * TM would cause any SPI transaction to abort. However, when
+	 * I tried that, SPI transactions would spontaneously abort,
+	 * making me assume that we needed a less aggressive pull-up
+	 * than is offered inside the AVR
+	 */
+#if SPI_SLAVE_PIN_0_3
+	PCMSK0 |= (1 << PCINT0);	/* Enable PCINT0 pin change */
+	PCICR |= (1 << PCIE0);		/* Enable pin change interrupt */
+
+	DDRB = ((DDRB & 0xf0) |
+		(1 << 3) |		/* MISO, output */
+		(0 << 2) |		/* MOSI, input */
+		(0 << 1) |		/* SCK, input */
+		(0 << 0));		/* SS, input */
+
+	PORTB = ((PORTB & 0xf0) |
+		 (1 << 3) |		/* MISO, output */
+		 (0 << 2) |		/* MOSI, no pull-up */
+		 (0 << 1) |		/* SCK, no pull-up */
+		 (1 << 0));		/* SS, pull-up */
+#endif
+#if SPI_SLAVE_PIN_2_5
+	PCMSK0 |= (1 << PCINT2);	/* Enable PCINT2 pin change */
+	PCICR |= (1 << PCIE0);		/* Enable pin change interrupt */
+
+	DDRB = ((DDRB & 0xf0) |
+		(0 << 5) |		/* SCK, input */
+		(1 << 4) |		/* MISO, output */
+		(0 << 3) |		/* MOSI, input */
+		(0 << 2));		/* SS, input */
+
+	PORTB = ((PORTB & 0xf0) |
+		 (0 << 5) |		/* SCK, no pull-up */
+		 (1 << 4) |		/* MISO, output */
+		 (0 << 3) |		/* MOSI, no pull-up */
+		 (1 << 2));		/* SS, pull-up */
+#endif	
+
+	SPCR = (0 << SPIE) |		/* Disable SPI interrupts */
+		(1 << SPE) |		/* Enable SPI */
+		(0 << DORD) |		/* MSB first */
+		(0 << MSTR) |		/* Slave mode */
+		(0 << CPOL) |		/* Clock low when idle */
+		(0 << CPHA);		/* Sample at leading clock edge */
+}