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/display.cc |  2 +-
 src/i2c.cc     | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/i2c.h      | 14 ++++++++++++++
 src/main.cc    | 14 ++++++++++++++
 4 files changed, 86 insertions(+), 1 deletion(-)
 create mode 100644 src/i2c.cc
 create mode 100644 src/i2c.h

diff --git a/src/display.cc b/src/display.cc
index 3bffacd..1cdc0a2 100644
--- a/src/display.cc
+++ b/src/display.cc
@@ -102,11 +102,11 @@ void Display::setString(const char *new_str)
 void Display::setString(char *new_str)
 {
 	int i;
-	reset();
 	for (i = 0; new_str[i] != 0; i++) {
 		string[i] = new_str[i];
 	}
 	string[i] = 0; // trailing null byte
+	reset();
 }
 
 /*
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);
+}
diff --git a/src/i2c.h b/src/i2c.h
new file mode 100644
index 0000000..818db23
--- /dev/null
+++ b/src/i2c.h
@@ -0,0 +1,14 @@
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <stdlib.h>
+
+#define I2C_EEPROM_ADDR 0x50
+
+class I2C {
+	public:
+		I2C() {};
+		void enable();
+		void xmit(int num_tx, int num_rx, uint8_t *txbuf, uint8_t *rxbuf);
+};
+
+extern I2C i2c;
diff --git a/src/main.cc b/src/main.cc
index 4398d02..0fb68ff 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -6,11 +6,16 @@
 
 #include "display.h"
 #include "font.h"
+#include "i2c.h"
 #include "modem.h"
 #include "system.h"
 
 int main (void)
 {
+	char testbuf[] = "..Olol I2C extra lang bla foo wololo moep   ";
+	char testbuf2[32];
+	testbuf[0] = 1;
+	testbuf[1] = 0;
 	// disable ADC to save power
 	PRR |= _BV(PRADC);
 
@@ -24,8 +29,17 @@ int main (void)
 
 	display.enable();
 	modem.enable();
+	i2c.enable();
 
 	sei();
+	//display.setString("tx");
+
+	i2c.xmit(64, 0, (uint8_t *)testbuf, (uint8_t *)testbuf);
+
+	//display.setString("rx");
+
+	i2c.xmit(2, 64, (uint8_t *)testbuf, (uint8_t *)testbuf2);
+	display.setString(testbuf2);
 
 	while (1) {
 		// nothing to do here, go to idle to save power
-- 
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