scoutos / scout_avr / bom / tiny-twi.c @ b3a1dae4
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#include <avr/io.h> |
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#include <avr/interrupt.h> |
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#include <util/delay.h> |
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#include "tiny-twi.h" |
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#define SDA PB0
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#define SCL PB2
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#define RECV_BUF_SIZE 2 |
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#define SEND_BUF_SIZE 100 |
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uint8_t address; |
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typedef enum { |
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IDLE, |
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ADDRESS, |
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SEND_READ_ACK, |
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SEND_WRITE_ACK, |
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SEND_DATA, |
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RECV_DATA, |
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RECV_ACK |
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} state_t; |
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state_t state; |
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uint8_t recv_idx; |
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uint8_t recv_data[RECV_BUF_SIZE]; |
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slave_rx_t onDataRecieved; |
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struct {
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uint8_t start; |
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uint8_t end; |
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uint8_t data[SEND_BUF_SIZE]; |
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bool full;
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} send_queue; |
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static void twi_set_ctr(char n) { |
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USISR = n; |
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} |
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static void twi_ready() { |
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USISR = _BV(USISIF) | _BV(USIOIF) | _BV(USIPF) | _BV(USIDC); |
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DDRB |= _BV(SCL); //SCL output
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DDRB &= ~_BV(SDA); //SDA input
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// enable start condition interrupt
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USICR |= _BV(USISIE); |
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// disable counter overflow interrupt
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USICR &= ~_BV(USIOIE); |
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state = IDLE; |
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} |
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static void twi_start() { |
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// enable counter overflow interrupt (fires after 8 bits)
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USICR |= _BV(USIOIE); |
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USISR = _BV(USISIF); |
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// zero counter
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twi_set_ctr(0);
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state = ADDRESS; |
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recv_idx = 0;
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} |
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static void twi_send_ack(char is_read) { |
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// set counter to 14
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twi_set_ctr(14);
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// set SDA low
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USIDR = 0;
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DDRB |= _BV(SDA); |
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// set state
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state = is_read? SEND_READ_ACK : SEND_WRITE_ACK; |
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} |
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static void twi_send_data() { |
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twi_set_ctr(0);
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if (send_queue.start == send_queue.end && !send_queue.full) {
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USIDR = 0;
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} else {
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USIDR = send_queue.data[send_queue.start++]; |
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if (send_queue.start == SEND_BUF_SIZE)
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send_queue.start = 0;
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send_queue.full = 0;
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} |
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DDRB |= _BV(SDA); |
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state = SEND_DATA; |
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} |
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static void twi_recv_ack() { |
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twi_set_ctr(14);
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DDRB &= ~_BV(SDA); |
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state = RECV_ACK; |
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} |
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ISR(USI_START_vect) { |
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twi_start(); |
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} |
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ISR(USI_OVF_vect) { |
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uint8_t input = USIDR; // TODO make sure this is correct
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switch (state) {
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case IDLE:
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// shouldn't reach here
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twi_ready(); |
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break;
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case ADDRESS:
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if (input >> 1 == address) { |
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// send ack
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twi_send_ack(input & 1);
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} else {
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// go back to listening for start condition
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twi_ready(); |
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} |
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break;
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case SEND_WRITE_ACK:
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if (recv_idx == RECV_BUF_SIZE) {
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twi_ready(); |
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onDataRecieved(recv_data, RECV_BUF_SIZE); |
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} else {
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DDRB &= ~_BV(SDA); |
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state = RECV_DATA; |
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} |
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break;
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case RECV_DATA:
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twi_send_ack(0);
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recv_data[recv_idx] = input; |
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recv_idx++; |
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break;
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case SEND_READ_ACK:
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twi_send_data(); |
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break;
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case SEND_DATA:
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twi_recv_ack(); |
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break;
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case RECV_ACK:
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if (input & 1) { |
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// received nak
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twi_ready(); |
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} else {
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// received ack
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twi_send_data(); |
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} |
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break;
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} |
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USISR = _BV(USIOIF) | (USISR & 0xF);
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} |
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void smb_init(slave_rx_t callback) {
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// TODO do we want USICS0 (3)?
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USICR = _BV(USIWM1) | _BV(USIWM0) | _BV(USICS1); |
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PORTB |= _BV(SDA) | _BV(SCL); |
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twi_ready(); |
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onDataRecieved = callback; |
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} |
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void smb_set_address(uint8_t addr) {
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address = addr; |
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} |
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void send_data(uint8_t* data, uint8_t length) {
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uint8_t i; |
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for (i=0; i<length && !send_queue.full; i++) { |
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send_queue.data[send_queue.end++] = data[i]; |
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if (send_queue.end == SEND_BUF_SIZE)
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send_queue.end = 0;
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if (send_queue.end == send_queue.start)
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send_queue.full = 1;
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} |
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} |
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void testCB(uint8_t* data, int length) { |
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send_data(data, length); |
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} |
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int main() {
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sei(); |
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smb_set_address(5);
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DDRB |= _BV(DDB4); |
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smb_init(testCB); |
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while(1); |
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} |