altos-avr: Add SPI-slave companion support

[fw/altos] / src-avr / ao_spi_slave.c

diff --git a/src-avr/ao_spi_slave.c b/src-avr/ao_spi_slave.c
new file mode 100644 (file)
index 0000000..5f1990d
--- /dev/null
+++ b/src-avr/ao_spi_slave.c
@@ -0,0 +1,101 @@
+/*
+ * 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 */
+}