From d6b2c7707b92f6daada2577dac51ba226f7b5046 Mon Sep 17 00:00:00 2001
From: Daniel Friesel <derf@finalrewind.org>
Date: Sun, 24 Jan 2016 16:42:58 +0100
Subject: I2C proof of concept: works!

---
 src/i2c.cc | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 src/i2c.cc

(limited to 'src/i2c.cc')

diff --git a/src/i2c.cc b/src/i2c.cc
new file mode 100644
index 0000000..37af104
--- /dev/null
+++ b/src/i2c.cc
@@ -0,0 +1,57 @@
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <util/delay.h>
+#include <stdlib.h>
+
+#include "i2c.h"
+
+I2C i2c;
+
+void I2C::enable()
+{
+	/*
+	 * Set I2C clock frequency to 100kHz.
+	 * freq = F_CPU / (16 + (2 * TWBR * TWPS) )
+	 * let TWPS = "00" = 1
+	 * -> TWBR = (F_CPU / 100000) - 16 / 2
+	 */
+	TWSR = 0; // the lower two bits control TWPS
+	TWBR = ((F_CPU / 100000UL) - 16) / 2;
+}
+
+// TODO Everything[tm] (error handling and generic code)
+// Also TODO: Use interrupts instead of polling
+void I2C::xmit(int num_tx, int num_rx, uint8_t *txbuf, uint8_t *rxbuf)
+{
+	int i;
+
+	if (num_tx) {
+		TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN);
+		while (!(TWCR & _BV(TWINT)));
+		TWDR = (I2C_EEPROM_ADDR << 1) | 0;
+		TWCR = _BV(TWINT) | _BV(TWEN);
+		while (!(TWCR & _BV(TWINT)));
+		for (i = 0; i < num_tx; i++) {
+			TWDR = txbuf[i];
+			TWCR = _BV(TWINT) | _BV(TWEN);
+			while (!(TWCR & _BV(TWINT)));
+		}
+	}
+	if (num_rx) {
+		TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN);
+		while (!(TWCR & _BV(TWINT)));
+		TWDR = (I2C_EEPROM_ADDR << 1) | 1;
+		TWCR = _BV(TWINT) | _BV(TWEN);
+		while (!(TWCR & _BV(TWINT)));
+		for (i = 0; i < num_rx; i++) {
+			if (i == num_rx-1) {
+				TWCR = _BV(TWINT) | _BV(TWEN);
+			} else {
+				TWCR = _BV(TWINT) | _BV(TWEN) | _BV(TWEA);
+			}
+			while (!(TWCR & _BV(TWINT)));
+			rxbuf[i] = TWDR;
+		}
+	}
+	TWCR = _BV(TWINT) | _BV(TWSTO) | _BV(TWEN);
+}
-- 
cgit v1.2.3