USB-I2C/firmware/i2c.h

/* Bit-banged open-drain I2C master: SCL=PD3, SDA=PD2 (external pull-ups required) */
#ifndef I2C_H
#define I2C_H

#include <stdint.h>
#include <stdbool.h>

enum { I2C_OK = 0, I2C_NACK_ADDR = 1, I2C_NACK_DATA = 2, I2C_BUS_ERR = 3 };

void    i2c_init(void);
void    i2c_set_delay(uint8_t d);   /* 0 = fastest, each step adds ~0.375 us per SCL period */
uint8_t i2c_lines(uint8_t pullup);  /* diag: bit0=SCL, bit1=SDA level; pullup=1 enables weak internal pull-ups */
uint8_t i2c_recover(void);         /* clock out stuck slave, then STOP */
/* wlen>0: write phase; rlen>0: read phase (repeated START if both);
 * wlen==0 && rlen==0: address probe. addr is the 7-bit address. */
uint8_t i2c_xfer(uint8_t addr, const uint8_t *w, uint8_t wlen, uint8_t *r, uint8_t rlen);

/* Split-phase access. i2c_start(): START (or repeated START) + address byte
 * (addr_rw = addr << 1 | R/W). A non-repeated start clears the error flag and
 * runs bus recovery if a line is stuck. Returns I2C_OK / I2C_NACK_ADDR / I2C_BUS_ERR. */
uint8_t i2c_start(uint8_t addr_rw, bool repeated);
uint8_t i2c_write(uint8_t b);      /* I2C_OK / I2C_NACK_DATA / I2C_BUS_ERR */
uint8_t i2c_read(bool ack);        /* ack=false on the last byte */
bool    i2c_bus_error(void);       /* clock-stretch timeout since last non-repeated start */
void    i2c_stop(void);

#endif