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