scoutos / scout_avr / bom / tiny-twi.c @ 90e5f3dd
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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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#define RECV_BUF_SIZE 2 |
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uint8_t address; |
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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; |
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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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static void twi_set_ctr(char n) { |
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USISR &= ~0x0F;
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USISR |= n; |
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} |
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static void twi_release_scl() { |
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DDRB &= ~_BV(DDB2); |
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} |
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static void twi_sink_sda() { |
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DDRB |= _BV(DDB0); |
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} |
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static void twi_release_sda() { |
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DDRB &= ~_BV(DDB0); |
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} |
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static void twi_ready() { |
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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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// zero counter
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twi_set_ctr(0);
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// enable counter overflow interrupt (fires after 8 bits)
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USICR |= _BV(USIOIE); |
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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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twi_sink_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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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 = USIBR; |
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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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twi_release_sda(); |
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state = RECV_DATA; |
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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] = USIBR; |
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recv_idx++; |
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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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} |
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break;
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case SEND_READ_ACK:
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twi_release_sda(); |
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// TODO write to USIDR
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state = SEND_DATA; |
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break;
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case SEND_DATA:
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break;
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case RECV_ACK:
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break;
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} |
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twi_release_scl(); |
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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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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 testCB(uint8_t* data, int length) { |
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PORTB |= _BV(PB4); |
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if (data[0]) |
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_delay_ms(1000);
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else
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_delay_ms(500);
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PORTB &= ~_BV(PB4); |
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} |
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int main() {
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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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} |