altos: Add i2c driver for avr chip

Signed-off-by: Keith Packard <keithp@keithp.com>

diff --git a/src/avr/ao_i2c_usart.c b/src/avr/ao_i2c_usart.c
new file mode 100644 (file)
index 0000000..60e35f8
--- /dev/null
+++ b/src/avr/ao_i2c_usart.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"
+
+/*
+ * Atmega32u4 TWI master mode (I2C)
+ */
+
+__xdata uint8_t        ao_i2c_mutex;
+
+/* Send bytes over I2C.
+ *
+ * This just polls; the I2C is set to go as fast as possible,
+ * so using interrupts would take way too long
+ */
+void
+ao_i2c_send(void __xdata *block, uint16_t len) __reentrant
+{
+       uint8_t *d = block;
+
+       ao_mutex_get(&ao_i2c_mutex);
+       while (len--) {
+               while (!(UCSR1A & (1 << UDRE1)));
+               UDR1 = *d++;
+               while (!(UCSR1A & (1 << RXC1)));
+               (void) UDR1;
+       }
+       ao_mutex_put(&ao_i2c_mutex);
+}
+
+/* Receive bytes over I2C.
+ *
+ * This sets up tow DMA engines, one reading the data and another
+ * writing constant values to the I2C transmitter as that is what
+ * clocks the data coming in.
+ */
+void
+ao_i2c_recv(void __xdata *block, uint16_t len) __reentrant
+{
+       uint8_t *d = block;
+
+       ao_mutex_get(&ao_i2c_mutex);
+       while (len--) {
+               while (!(UCSR1A & (1 << UDRE1)));
+               UDR1 = 0;
+               while (!(UCSR1A & (1 << RXC1)));
+               *d++ = UDR1;
+       }
+       ao_mutex_put(&ao_i2c_mutex);
+}
+
+#define XCK1_DDR       DDRD
+#define XCK1_PORT      PORTD
+#define XCK1           PORTD5
+#define XMS1_DDR       DDRE
+#define XMS1_PORT      PORTE
+#define XMS1           PORTE6
+
+void
+ao_i2c_init(void)
+{
+       /* Ensure the TWI is powered */
+
+       /*
+        * Set pin directions
+        */
+       XCK1_DDR |= (1 << XCK1);
+
+       /* Clear chip select (which is negated) */
+       XMS1_PORT |= (1 < XMS1);
+       XMS1_DDR |= (1 << XMS1);
+
+       /* Set baud register to zero (required before turning transmitter on) */
+       UBRR1 = 0;
+
+       UCSR1C = ((0x3 << UMSEL10) |    /* Master I2C mode */
+                 (0 << UCSZ10) |       /* I2C mode 0 */
+                 (0 << UCPOL1));       /* I2C mode 0 */
+
+       /* Enable transmitter and receiver */
+       UCSR1B = ((1 << RXEN1) |
+                 (1 << TXEN1));
+
+       /* It says that 0 is a legal value; we'll see... */
+       UBRR1 = 0;
+}