From db9445ceba9830b0d36c3a0d20c6dc2a4d6b1083 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?King=20K=C3=A9vin?= <kingkevin@cuvoodoo.info>
Date: Thu, 26 Feb 2015 13:49:58 +0100
Subject: [PATCH] add TWI library

---
 lib/twi.c | 239 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/twi.h |  42 ++++++++++
 2 files changed, 281 insertions(+)
 create mode 100644 lib/twi.c
 create mode 100644 lib/twi.h

diff --git a/lib/twi.c b/lib/twi.c
new file mode 100644
index 0000000..d0a540c
--- /dev/null
+++ b/lib/twi.c
@@ -0,0 +1,239 @@
+/* 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, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ *
+ */
+/* This library handles the Two-Wire Interface (TWI)/Inter-Integrated Circuit (I²C) configuration
+ * based on demo by Ruwan Jayanetti from AVR libc examples
+ * http://www.nongnu.org/avr-libc/user-manual/group__twi__demo.html
+ */
+#include <stdint.h> // Standard Integer Types
+#include <stdlib.h> // General utilities
+#include <stdbool.h> // Boolean
+
+#include <avr/io.h>  // AVR device-specific IO definitions
+#include <util/twi.h> // 2-wire TWSR values
+
+#include <twi.h> // definitions
+
+/* initialize 2-wire interface */
+void twi_init(void)
+{
+	TWSR &= ~((1<<TWPS0)|(1<<TWPS1)); // set TWI prescaler to 1X
+#if F_CPU < 3600000UL
+	TWBR = 10; // smallest TWBR value
+#else
+	TWBR = (uint8_t)((F_CPU/F_TWI-16)/2); // set TWI clock speed
+#endif
+}
+
+/* read <len> bytes inyo <buf> using 2-wire interface, starting at <addr>
+ * returns if it succeeded
+ * 16 bits address is not supported
+ */
+bool twi_read_bytes(uint8_t addr, uint8_t len, uint8_t *buf)
+{
+	uint16_t retry = 0; // number of retries
+	bool rc = false; // return code
+
+	/* number of times to retry */
+restart:
+	if (retry++ >= MAX_ITER) {
+		return false;
+	}
+
+	/* first cycle: master transmitter mode */
+start:
+
+	/* send start */
+	TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN); // send start condition
+	while ((TWCR & (1<<TWINT)) == 0); // wait for transmission
+	switch (TW_STATUS) {
+		case TW_REP_START: // OK, but should not happen
+		case TW_START:
+			break;
+		case TW_MT_ARB_LOST: // re-arbitrate
+			goto start;
+		default:
+			return -1;
+	}
+
+	/* send SLA+W */
+	TWDR = SLA | TW_WRITE;
+	TWCR = (1<<TWINT) | (1<<TWEN); // clear interrupt to start transmission
+	while ((TWCR & (1<<TWINT)) == 0); // wait for transmission
+	switch (TW_STATUS) {
+		case TW_MT_SLA_ACK:
+			break;
+		case TW_MT_SLA_NACK: // nack during select: device busy writing
+			goto restart;
+		case TW_MT_ARB_LOST: // re-arbitrate
+			goto start;
+		default:
+			goto stop; // must send stop condition
+	}
+
+	/* send memory address */
+	TWDR = addr;
+	TWCR = (1<<TWINT) | (1<<TWEN); // clear interrupt to start transmission
+	while ((TWCR & (1<<TWINT)) == 0); // wait for transmission
+	switch (TW_STATUS) {
+		case TW_MT_DATA_ACK:
+			break;
+		case TW_MT_DATA_NACK:
+			goto stop;
+		case TW_MT_ARB_LOST:
+			goto start;
+		default:
+			goto stop; // must send stop condition
+	}
+
+	/* next cycle(s): master receiver mode */
+
+	/* repeat start */
+	TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN); // send start condition
+	while ((TWCR & (1<<TWINT)) == 0); // wait for transmission
+	switch (TW_STATUS) {
+		case TW_START: // OK, but should not happen
+		case TW_REP_START:
+			break;
+		case TW_MT_ARB_LOST:
+			goto start;
+		default:
+			goto stop;
+	}
+
+	/* send SLA+R */
+	TWDR = SLA | TW_READ;
+	TWCR = (1<<TWINT) | (1<<TWEN); // clear interrupt to start transmission
+	while ((TWCR & (1<<TWINT)) == 0); // wait for transmission
+	switch (TW_STATUS) {
+		case TW_MR_SLA_ACK:
+			break;
+		case TW_MR_SLA_NACK:
+			goto stop;
+		case TW_MR_ARB_LOST:
+			goto start;
+		default:
+			goto stop;
+	}
+
+	/* read bytes */
+	while (len > 0) {
+		if (len > 1) {
+			TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWEA); // send ACK
+		} else { // last byte
+			TWCR = (1<<TWINT) | (1<<TWEN); // send NACK
+		}
+		while ((TWCR & (1<<TWINT)) == 0); // wait for transmission
+		switch (TW_STATUS) {
+			case TW_MR_DATA_NACK: // last byte received
+				len = 1; // force end of loop (save as in next case)
+			case TW_MR_DATA_ACK:
+				*buf++ = TWDR;
+				len--;
+				break;
+			default:
+				goto stop;
+		}
+	}
+	rc = true;
+
+	/* send stop */
+stop:
+	TWCR = (1<<TWINT) | (1<<TWSTO) | (1<<TWEN); // send stop condition
+	return rc;
+}
+
+/* write <len> bytes from <buf> on 2-wire interface starting at <addr>
+ * returns if it successed
+ * 16 bits address is not supported
+ * ensure yourself the size of pages to be written
+ */
+bool twi_write_bytes(uint8_t addr, uint8_t len, uint8_t *buf)
+{
+	uint16_t retry = 0; // number of retries
+	bool rc = false; // return code
+
+	/* number of times to retry */
+restart:
+	if (retry++ >= MAX_ITER) {
+		return false;
+	}
+
+	/* master transmit mode */
+start:
+
+	/* start */
+	TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN); // send start condition
+	while ((TWCR & (1<<TWINT)) == 0); // wait for transmission
+	switch (TW_STATUS) {
+		case TW_REP_START: // OK, but should not happen
+		case TW_START:
+			break;
+		case TW_MT_ARB_LOST:
+			goto start;
+		default:
+			return false; // error: not in start condition
+	}
+
+	/* send SLA+W */
+	TWDR = SLA | TW_WRITE;
+	TWCR = (1<<TWINT) | (1<<TWEN); // clear interrupt to start transmission
+	while ((TWCR & (1<<TWINT)) == 0); // wait for transmission
+	switch (TW_STATUS) {
+		case TW_MT_SLA_ACK:
+			break;
+		case TW_MT_SLA_NACK: // nack during select: device busy writing
+			goto restart;
+		case TW_MT_ARB_LOST: // re-arbitrate
+			goto start;
+		default:
+			goto stop; // must send stop condition
+	}
+
+	/* send address */
+	TWDR = addr;
+	TWCR = (1<<TWINT) | (1<<TWEN); // clear interrupt to start transmission
+	while ((TWCR & (1<<TWINT)) == 0); // wait for transmission
+	switch (TW_STATUS) {
+		case TW_MT_DATA_ACK:
+			break;
+		case TW_MT_DATA_NACK:
+			goto stop;
+		case TW_MT_ARB_LOST:
+			goto start;
+		default:
+			goto stop;
+	}
+
+	/* write bytes */
+	for (; len > 0; len--) {
+		TWDR = *buf++;
+		TWCR = (1<<TWINT) | (1<<TWEN); // start transmission
+		while ((TWCR & (1<<TWINT)) == 0); // wait for transmission
+		switch (TW_STATUS) {
+			case TW_MT_DATA_NACK:  // device write protected
+				goto stop;
+			case TW_MT_DATA_ACK:
+				break;
+			default:
+				goto stop;
+		}
+	}
+	rc = true;
+
+	/* send stop */
+stop:
+	TWCR = (1<<TWINT) | (1<<TWSTO) | (1<<TWEN); // send stop condition
+	return rc;
+}
diff --git a/lib/twi.h b/lib/twi.h
new file mode 100644
index 0000000..05e4be6
--- /dev/null
+++ b/lib/twi.h
@@ -0,0 +1,42 @@
+/* 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, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ *
+ */
+/* This library handles the Two-Wire Interface (TWI)/Inter-Integrated Circuit (I²C) configuration */
+
+/* TWI/I2C clock speed, in Hz */
+#define F_TWI 100000UL
+/*
+ * Maximal number of iterations to wait for a device to respond for a selection
+ * Should be large enough to allow for a pending write to* complete, but low enough to properly abort an infinite loop in case a slave is broken or not present at all. 
+ * With 100 kHz TWI clock, transfering the start condition and SLA+R/W packet takes about 10 µs.
+ * The longest write period is supposed to not exceed ~ 10 ms.
+ * Thus, normal operation should not require more than 100 iterations to get the device to respond to a selection.
+ */
+#define MAX_ITER 400
+/* card (slave) address (7 MSB) */
+#define SLA 0xA0
+
+/* initialize 2-wire interface */
+void twi_init(void);
+/* read <len> bytes inyo <buf> using 2-wire interface, starting at <addr>
+ * returns if it succeeded
+ * 16 bits address is not supported
+ */
+bool twi_read_bytes(uint8_t addr, uint8_t len, uint8_t *buf);
+/* write <len> bytes from <buf> on 2-wire interface starting at <addr>
+ * returns if it successed
+ * 16 bits address is not supported
+ * ensure yourself the size of pages to be written
+ */
+bool twi_write_bytes(uint8_t addr, uint8_t len, uint8_t *buf);