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/* @file i2c.c
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* @brief
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* In the case where you have master sends and then a master request to the same
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* address, you will not give up control of the line because the send and
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* request addresses are seen as different addresses. In between it will send a
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* restart but will not give up the line.
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*
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* @author CMU Robotics Club, Kevin Woo, Sursh Nidhiry
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* @bug Not tested.
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*/
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#include <avr/interrupt.h> |
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#include <util/twi.h> |
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#include "i2c.h" |
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#include "ring_buffer.h" |
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/**
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* @defgroup i2c I2C
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*
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* @brief Provides Inter-Interconnected-Communications (I2C)
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*
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* Initiates I2C functions on an ATMega128 which has a fully hardware Two Wire
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* Interface (TWI) module. Any Atmel chip with this hardware should be able to
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* use the software.
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*
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* This code will operate in a multi-master enviornment and can be either a
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* slave or a master at any time (as long as they are not one or the other at
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* the moment. You can queue up multiple transmission modes in the buffer up to
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* the buffer size. The buffer is implemented as a ring buffer.
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*
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* It is implemented using callback functions. Whenever you want to send a packet
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* you can call the built in send function (as a master) and it will send an array
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* of bytes. Master recieve and slave send/receive are all handled by the call back
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* functions. It is up to the end user to create functions that will handle the
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* receiving of packets. Their functions will be called with every byte recieved
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* so you must either buffer the inputs or handle each one separately.
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*
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* On errors we will simply flush the entire buffer.
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*
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* For information on how I2C operates, read the wikipedia article
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* http://en.wikipedia.org/wiki/I2c
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* for a good explanation of how it works.
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* @{
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*/
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/**
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* @brief Set bit rate 12 = 100kbit/s (max speed setting is 10 for an
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* 8 MHz clock). It is a divider, so the lower the number the faster the speed.
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*/
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#define I2C_BIT_RATE_DIVIDER 0x0C |
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static int start_flag; |
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static fun_mrecv_t master_recv_function;
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static fun_srecv_t slave_recv_function;
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static fun_send_t slave_send_function;
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RING_BUFFER_NEW(i2c_buffer, 128, char, i2c_write_buff, i2c_addr_buff); |
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/**
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* @brief Initializes the i2c module.
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*
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* Initializes the I2C module to start listening on the i2c lines. If the callback functions
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* are not set to null they will be called when that transmission mode is called. The address
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* is your address that you will listen to when you are not the master.
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*
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* @param addr Your address on the I2C bus.
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* @param master_recv The address of the function to call when you receive a byte when you are a
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* master.
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* @param slave_recv The address of the function to call when you are a slave you receive data
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* from the master
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* @param slave_send The address of the function to call when you are a slave and the master
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* requests data from you.
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**/
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int i2c_init(char addr, fun_mrecv_t master_recv, fun_srecv_t slave_recv, fun_send_t slave_send) { |
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master_recv_function = master_recv; |
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slave_recv_function = slave_recv; |
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slave_send_function = slave_send; |
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RING_BUFFER_CLEAR(i2c_write_buff); |
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RING_BUFFER_CLEAR(i2c_addr_buff); |
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/* enables twi interrupt, automatic ack sending, and all twi hardware */
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TWCR = (_BV(TWEA) | _BV(TWEN) | _BV(TWIE)); |
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/* sets the bit rate of data transmission */
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TWBR = I2C_BIT_RATE_DIVIDER; |
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/* sets the address (it is stored in the 7 most significant bits) and allows
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* global messages to be accepted */
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TWAR = (addr << 1) | 1; |
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return 0; |
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} |
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/**
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* @brief Sends a byte array over I2C as a master
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*
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* Will perform a send over I2C to the destination from data for the ammount of
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* bytes that bytes is.
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*
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* @param dest Destination address of the data on the I2C bus.
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* @param data The pointer to the byte array of data
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* @param bytes The amount of bytes long that the byte array is. This is how
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* many bytes from the array that the function will send.
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**/
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int i2c_send(char dest, char *data, size_t bytes) { |
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int i;
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/* adding data to be sent to ring buffers is not atomic,
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* so disable interrupts */
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cli(); |
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for(i = 0; i < bytes; i++) { |
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if(RING_BUFFER_FULL(i2c_write_buff)) {
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sei(); |
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return -1; |
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} |
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RING_BUFFER_ADD(i2c_write_buff, data[i]); |
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RING_BUFFER_ADD(i2c_addr_buff, dest << 1);
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} |
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/* re-enable the interrupts */
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sei(); |
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/* send the start bit, only if this device is not currently master */
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if(!start_flag) {
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start_flag = 1;
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TWCR |= _BV(TWSTA); |
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TWCR |= _BV(TWINT); |
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} |
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return 0; |
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} |
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/**
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* @brief Send a master request to the destination
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*
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* Sends a request of data from the target address and calls
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* the callback function to handle data as it comes in. This function will
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* not work if the slave has not informationt to send or has nothing implemented
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* to send it.
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*
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* @param dest The destination that we want to receive information from.
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**/
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int i2c_request(char dest) { |
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if(RING_BUFFER_FULL(i2c_write_buff))
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return -1; |
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RING_BUFFER_ADD(i2c_write_buff, 0);
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RING_BUFFER_ADD(i2c_addr_buff, (dest << 1) | 1); |
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if(!start_flag) {
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start_flag = 1;
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TWCR |= _BV(TWSTA); |
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TWCR |= _BV(TWINT); |
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} |
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return 0; |
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} |
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/**
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* @brief Interrupt to handle I2C interrupts from the I2C hardware.
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*
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* Uses the status codes from the I2C register to handle the events
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* needed to advance in I2C stages. For instance, you will get a bit for
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* receiving a start ack, then a address ack, then a data ack, etc.
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* The events are handled in each switch case. The status codes are defined
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* by avr-gcc in /util/twi.h but are the same codes as the Atmel documentation.
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*
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* Bytes are sent by popping off the ring buffer. It also will keep track
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* of what modes the send is in.
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*
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* Errors are handled here as well.
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**/
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/* @} */
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ISR(TWI_vect) { |
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static char data_to_send; |
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static char addr_to_send = -1; |
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char addr, statusCode;
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//Get status code (only upper 5 bits)
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statusCode = (TWSR & 0xF8);
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switch (statusCode) {
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//Start sent successfully
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case TW_START:
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case TW_REP_START:
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/* Send address and write
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* ring_buffer will not be empty */
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RING_BUFFER_REMOVE(i2c_addr_buff, addr_to_send); |
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RING_BUFFER_REMOVE(i2c_write_buff, data_to_send); |
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/* first send the address */
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TWDR = addr_to_send; |
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//Turn off start bits
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TWCR &= ~_BV(TWSTA); |
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break;
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//Master Transmit - Address sent succesfully
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case TW_MT_SLA_ACK:
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//Send byte
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TWDR = data_to_send; |
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PORTG &= ~_BV(PG2); |
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break;
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//Master Transmit - Data sent succesfully
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case TW_MT_DATA_ACK:
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//If there is still data to send
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if(!RING_BUFFER_EMPTY(i2c_write_buff)) {
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RING_BUFFER_PEEK(i2c_addr_buff, addr); |
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//Still data for this address
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if (addr == addr_to_send) {
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RING_BUFFER_REMOVE(i2c_addr_buff, addr); |
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RING_BUFFER_REMOVE(i2c_write_buff, TWDR); |
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break;
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//No more data for this address, data for another address -> resend start
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} else {
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TWCR |= _BV(TWSTA); |
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break;
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} |
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} |
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/* there are no bytes to send */
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TWCR |= _BV(TWSTO); |
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start_flag = 0;
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break;
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//Master Transmit - Slave sends a nack, transmit is done
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case TW_MT_DATA_NACK:
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PORTG |= _BV(PG2); |
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TWCR |= _BV(TWSTO); |
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start_flag = 0;
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break;
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//Master Receive - Address sent succesfully
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case TW_MR_SLA_ACK:
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PORTG |= _BV(PG2); |
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break;
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//Master Receive - Data received succesfully
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case TW_MR_DATA_ACK:
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if(master_recv_function) {
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if(!master_recv_function(TWDR)) {
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TWCR &= ~_BV(TWEA); |
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} |
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} |
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break;
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//Master Receive - Slave sends a nack, transmission is done
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case TW_MR_DATA_NACK:
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TWCR |= _BV(TWEA); |
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//If there is still data to send
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if(!RING_BUFFER_EMPTY(i2c_write_buff)) {
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TWCR |= _BV(TWSTA); |
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break;
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} |
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/* there are no bytes to send */
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TWCR |= _BV(TWSTO); |
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start_flag = 0;
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break;
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//Slave Transmit - Address received
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case TW_ST_SLA_ACK:
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break;
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//Slave Transmit - Nack received, no data requsted
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case TW_ST_DATA_NACK:
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break;
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//Slave Transmit - Data requested, ack received
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case TW_ST_DATA_ACK:
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if (slave_send_function) {
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TWDR = slave_send_function(); |
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} |
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break;
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//Slave Receive - Address received
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case TW_SR_SLA_ACK:
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break;
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//Slave Receive - Data received, ack returned
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case TW_SR_DATA_ACK:
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if(slave_recv_function) {
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slave_recv_function(TWDR); |
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} |
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break;
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//Stop sent
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case TW_SR_STOP:
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break;
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//Problem on the bus, reset everything
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default:
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TWCR |= _BV(TWSTO); |
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start_flag = 0;
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RING_BUFFER_CLEAR(i2c_write_buff); |
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RING_BUFFER_CLEAR(i2c_addr_buff); |
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} |
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/* Toggle TWINT so that it resets and executes the commands */
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TWCR |= _BV(TWINT); |
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} |