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+/*
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+ twi.c - Stripped-down TWI/I2C library
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+ Copyright (c) 2006 Nicholas Zambetti. All right reserved.
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+
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+ This library is free software; you can redistribute it and/or
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+ modify it under the terms of the GNU Lesser General Public
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+ License as published by the Free Software Foundation; either
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+ version 2.1 of the License, or (at your option) any later version.
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+
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+ This library is distributed in the hope that it will be useful,
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+ but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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+ Lesser General Public License for more details.
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+
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+ You should have received a copy of the GNU Lesser General Public
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+ License along with this library; if not, write to the Free Software
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+ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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+
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+ Modified 2012 by Todd Krein (todd@krein.org) to implement repeated starts
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+*/
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+
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+
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+#include <math.h>
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+#include "config.h"
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+#include "fastio.h"
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+#include "twi.h"
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+
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+
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+void twi_init(void)
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+{
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+ // activate internal pullups for twi.
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+ WRITE(SDA_PIN, 1);
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+ WRITE(SCL_PIN, 1);
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+
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+ // initialize twi prescaler and bit rate
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+ TWSR &= ~(_BV(TWPS0) | _BV(TWPS1));
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+ TWBR = ((F_CPU / TWI_FREQ) - 16) / 2;
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+
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+ /* twi bit rate formula from atmega128 manual pg 204
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+ SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
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+ note: TWBR should be 10 or higher for master mode
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+ It is 72 for a 16mhz Wiring board with 100kHz TWI */
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+}
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+
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+void twi_disable(void)
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+{
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+ // deactivate internal pullups for twi.
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+ WRITE(SDA_PIN, 0);
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+ WRITE(SCL_PIN, 0);
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+}
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+
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+
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+static void twi_stop()
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+{
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+ TWCR = _BV(TWEN) | _BV(TWINT) | _BV(TWSTO);
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+}
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+
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+
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+static uint8_t twi_wait(uint8_t status)
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+{
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+ while(!(TWCR & _BV(TWINT)));
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+ if(TW_STATUS != status)
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+ {
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+ twi_stop();
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+ return 1;
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+ }
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+ return 0;
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+}
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+
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+
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+static uint8_t twi_start(uint8_t address, uint8_t reg)
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+{
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+ // send start condition
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+ TWCR = _BV(TWEN) | _BV(TWINT) | _BV(TWSTA);
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+ if(twi_wait(TW_START))
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+ return 1;
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+
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+ // send address
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+ TWDR = TW_WRITE | (address << 1);
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+ TWCR = _BV(TWEN) | _BV(TWINT);
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+ if(twi_wait(TW_MT_SLA_ACK))
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+ return 2;
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+
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+ // send register
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+ TWDR = reg;
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+ TWCR = _BV(TWEN) | _BV(TWINT);
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+ if(twi_wait(TW_MT_DATA_ACK))
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+ return 3;
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+
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+ return 0;
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+}
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+
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+
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+uint8_t twi_r8(uint8_t address, uint8_t reg, uint8_t* data)
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+{
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+ if(twi_start(address, reg))
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+ return 1;
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+
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+ // repeat start
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+ TWCR = _BV(TWEN) | _BV(TWINT) | _BV(TWSTA);
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+ if(twi_wait(TW_REP_START))
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+ return 2;
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+
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+ // start receiving
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+ TWDR = TW_READ | (address << 1);
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+ TWCR = _BV(TWEN) | _BV(TWINT);
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+ if(twi_wait(TW_MR_SLA_ACK))
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+ return 3;
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+
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+ // receive data
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+ TWCR = _BV(TWEN) | _BV(TWINT);
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+ if(twi_wait(TW_MR_DATA_NACK))
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+ return 4;
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+
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+ *data = TWDR;
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+
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+ // send stop
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+ twi_stop();
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+ return 0;
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+}
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+
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+
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+uint8_t twi_w8(uint8_t address, uint8_t reg, uint8_t data)
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+{
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+ if(twi_start(address, reg))
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+ return 1;
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+
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+ // send data
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+ TWDR = data;
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+ TWCR = _BV(TWEN) | _BV(TWINT);
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+ if(twi_wait(TW_MT_DATA_ACK))
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+ return 2;
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+
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+ // send stop
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+ twi_stop();
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+ return 0;
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+}
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