+/*
+ * 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"
+
+__xdata struct ao_fifo ao_spi_slave_rx_fifo;
+__xdata struct ao_fifo ao_spi_slave_tx_fifo;
+
+static volatile uint8_t ao_spi_slave_tx_started;
+
+static void
+ao_spi_slave_tx_start(void)
+{
+ if (!ao_spi_slave_tx_started && !ao_fifo_empty(ao_spi_slave_tx_fifo)) {
+ ao_spi_slave_tx_started = 1;
+ ao_fifo_remove(ao_spi_slave_tx_fifo, SPDR);
+ }
+}
+
+ISR(SPI_STC_vect)
+{
+ uint8_t spsr;
+
+ spsr = SPSR;
+ if (SPIF & (1 << SPIF)) {
+ uint8_t byte = SPDR;
+ if (!ao_fifo_full(ao_spi_slave_rx_fifo))
+ ao_fifo_insert(ao_spi_slave_rx_fifo, byte);
+ ao_spi_slave_tx_started = 0;
+ ao_spi_slave_tx_start();
+ ao_wakeup(&ao_spi_slave_rx_fifo);
+ ao_wakeup(&ao_spi_slave_tx_fifo);
+ }
+}
+
+static void
+ao_spi_slave_put(uint8_t b) __critical
+{
+ cli();
+ while (ao_fifo_full(ao_spi_slave_tx_fifo))
+ ao_sleep(&ao_spi_slave_tx_fifo);
+ ao_fifo_insert(ao_spi_slave_tx_fifo, b);
+ ao_spi_slave_tx_start();
+ sei();
+}
+
+static uint8_t
+ao_spi_slave_get(void) __critical
+{
+ uint8_t b;
+
+ cli();
+ while (ao_fifo_empty(ao_spi_slave_rx_fifo))
+ ao_sleep(&ao_spi_slave_rx_fifo);
+ ao_fifo_remove(ao_spi_slave_rx_fifo, b);
+ sei();
+ return b;
+}
+
+void
+ao_spi_slave_read(uint8_t *data, int len)
+{
+ while (len--) {
+ ao_spi_slave_put(0);
+ *data++ = ao_spi_slave_get();
+ }
+}
+
+void
+ao_spi_slave_write(uint8_t *data, int len)
+{
+ while (len--) {
+ ao_spi_slave_put(*data++);
+ (void) ao_spi_slave_get();
+ }
+}
+
+void
+ao_spi_slave_init(void)
+{
+ SPCR = (1 << SPIE) | /* Enable 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 */
+}