Revision c4f160ba
Adding partly finished attiny i2c code
scout_avr/bom/tiny-twi.c | ||
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#include <avr/io.h> |
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#include <avr/interrupt.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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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_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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// TODO somehow release SCL following the ovf interrupt |
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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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// 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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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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// TODO callback |
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} |
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break; |
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case SEND_READ_ACK: |
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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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} |
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void smb_init() { |
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state = START; |
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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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} |
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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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