1 files changed, 146 insertions, 0 deletions
diff --git a/src/arch/arduino-nano/driver/i2c.cc b/src/arch/arduino-nano/driver/i2c.cc
new file mode 100644
index 0000000..a644ca9
--- /dev/null
+++ b/src/arch/arduino-nano/driver/i2c.cc
@@ -0,0 +1,146 @@
+#include "driver/i2c.h"
+#include <avr/io.h>
+
+/*
+ * Send an I2C (re)start condition and the EEPROM address in read mode. Returns
+ * after it has been transmitted successfully.
+ */
+static signed char i2c_start_read(unsigned char addr)
+{
+	TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN);
+	while (!(TWCR & _BV(TWINT)));
+	if (!(TWSR & 0x18)) // 0x08 == START ok, 0x10 == RESTART ok
+		return -1;
+
+	// Note: The R byte ("... | 1") causes the TWI momodule to switch to
+	// Master Receive mode
+	TWDR = (addr << 1) | 1;
+	TWCR = _BV(TWINT) | _BV(TWEN);
+	while (!(TWCR & _BV(TWINT)));
+	if (TWSR != 0x40) // 0x40 == SLA+R transmitted, ACK receveid
+		return -2;
+
+	return 0;
+}
+
+/*
+ * Send an I2C (re)start condition and the EEPROM address in write mode.
+ * Returns after it has been transmitted successfully.
+ */
+static signed char i2c_start_write(unsigned char addr)
+{
+	TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN);
+	while (!(TWCR & _BV(TWINT)));
+	if (!(TWSR & 0x18)) // 0x08 == START ok, 0x10 == RESTART ok
+		return -1;
+
+	TWDR = (addr<< 1) | 0;
+	TWCR = _BV(TWINT) | _BV(TWEN);
+	while (!(TWCR & _BV(TWINT)));
+	if (TWSR != 0x18) // 0x18 == SLA+W transmitted, ACK received
+		return -2;
+
+	return 0;
+}
+
+/*
+ * Send an I2C stop condition.
+ */
+static signed char i2c_stop()
+{
+	TWCR = _BV(TWINT) | _BV(TWSTO) | _BV(TWEN);
+}
+
+/*
+ * Sends len bytes to the EEPROM. Note that this method does NOT
+ * send I2C start or stop conditions.
+ */
+static signed char i2c_send(uint8_t len, uint8_t *data)
+{
+	uint8_t pos = 0;
+
+	for (pos = 0; pos < len; pos++) {
+		TWDR = data[pos];
+		TWCR = _BV(TWINT) | _BV(TWEN);
+		while (!(TWCR & _BV(TWINT)));
+		if (TWSR != 0x28) // 0x28 == byte transmitted, ACK received
+			return pos;
+	}
+
+	return pos;
+}
+
+/*
+ * Receives len bytes from the EEPROM into data. Note that this method does
+ * NOT send I2C start or stop conditions.
+ */
+static signed char i2c_receive(uint8_t len, uint8_t *data)
+{
+	uint8_t pos = 0;
+
+	for (pos = 0; pos < len; pos++) {
+		if (pos == len-1) {
+			// Don't ACK the last byte
+			TWCR = _BV(TWINT) | _BV(TWEN);
+		} else {
+			// Automatically send ACK
+			TWCR = _BV(TWINT) | _BV(TWEN) | _BV(TWEA);
+		}
+		while (!(TWCR & _BV(TWINT)));
+		data[pos] = TWDR;
+		/*
+		 * No error handling here -- We send the acks, the EEPROM only
+		 * supplies raw data, so there's no way of knowing whether it's still
+		 * talking to us or we're just reading garbage.
+		 */
+	}
+
+	return pos;
+}
+
+signed char I2C::setup()
+{
+	TWSR = 0;
+	TWBR = ((F_CPU / 100000UL) - 16) / 2;
+
+	return 0;
+}
+
+void I2C::scan(unsigned int *results)
+{
+	for (unsigned char address = 0; address < 128; address++) {
+		if (i2c_start_read(address) == 0) {
+			results[address / (8 * sizeof(unsigned int))] |= 1 << (address % (8 * sizeof(unsigned int)));
+		}
+	}
+	i2c_stop();
+}
+
+signed char I2C::xmit(unsigned char address,
+		unsigned char tx_len, unsigned char *tx_buf,
+		unsigned char rx_len, unsigned char *rx_buf)
+{
+	unsigned char i;
+
+	if (tx_len) {
+		if (i2c_start_write(address) < 0) {
+			return -1;
+		}
+		if (i2c_send(tx_len, tx_buf) < 0) {
+			return -1;
+		}
+	}
+	if (rx_len) {
+		if (i2c_start_read(address) < 0) {
+			return -1;
+		}
+		if (i2c_receive(rx_len, rx_buf) < 0) {
+			return -1;
+		}
+	}
+
+	i2c_stop();
+	return 0;
+}
+
+I2C i2c;