I2C wrapper functions for Linux userspace i2c-dev devices.
#include <periphery/i2c.h>
/* Primary Functions */
i2c_t *i2c_new(void);
int i2c_open(i2c_t *i2c, const char *device);
int i2c_transfer(i2c_t *i2c, struct i2c_msg *msgs, size_t count);
int i2c_close(i2c_t *i2c);
void i2c_free(i2c_t *i2c);
/* Miscellaneous */
int i2c_fd(i2c_t *i2c);
int i2c_tostring(i2c_t *i2c, char *str, size_t len);
/* Error Handling */
int i2c_errno(i2c_t *i2c);
const char *i2c_errmsg(i2c_t *i2c);
/* struct i2c_msg from <linux/i2c.h>:
struct i2c_msg {
__u16 addr;
__u16 flags;
#define I2C_M_TEN 0x0010
#define I2C_M_RD 0x0001
#define I2C_M_STOP 0x8000
#define I2C_M_NOSTART 0x4000
#define I2C_M_REV_DIR_ADDR 0x2000
#define I2C_M_IGNORE_NAK 0x1000
#define I2C_M_NO_RD_ACK 0x0800
#define I2C_M_RECV_LEN 0x0400
__u16 len;
__u8 *buf;
};
*/i2c_t *i2c_new(void);Allocate an I2C handle.
Returns a valid handle on success, or NULL on failure.
int i2c_open(i2c_t *i2c, const char *device);Open the i2c-dev device at the specified path (e.g. "/dev/i2c-1").
i2c should be a valid pointer to an allocated I2C handle structure.
Returns 0 on success, or a negative I2C error code on failure.
int i2c_transfer(i2c_t *i2c, struct i2c_msg *msgs, size_t count);Transfer count number of struct i2c_msg I2C messages.
i2c should be a valid pointer to an I2C handle opened with i2c_open(). msgs should be a pointer to an array of struct i2c_msg (defined in linux/i2c.h).
Each I2C message structure (see above) specifies the transfer of a consecutive number of bytes to a slave address. The slave address, message flags, buffer length, and pointer to a byte buffer should be specified in each message. The message flags specify whether the message is a read (I2C_M_RD) or write (0) transaction, as well as additional options selected by the bitwise OR of their bitmasks.
Returns 0 on success, or a negative I2C error code on failure.
int i2c_close(i2c_t *i2c);Close the i2c-dev device.
i2c should be a valid pointer to an I2C handle opened with i2c_open().
Returns 0 on success, or a negative I2C error code on failure.
void i2c_free(i2c_t *i2c);Free an I2C handle.
int i2c_fd(i2c_t *i2c);Return the file descriptor (for the underlying i2c-dev device) of the I2C handle.
i2c should be a valid pointer to an I2C handle opened with i2c_open().
This function is a simple accessor to the I2C handle structure and always succeeds.
int i2c_tostring(i2c_t *i2c, char *str, size_t len);Return a string representation of the I2C handle.
i2c should be a valid pointer to an I2C handle opened with i2c_open().
This function behaves and returns like snprintf().
int i2c_errno(i2c_t *i2c);Return the libc errno of the last failure that occurred.
i2c should be a valid pointer to an I2C handle opened with i2c_open().
const char *i2c_errmsg(i2c_t *i2c);Return a human readable error message of the last failure that occurred.
i2c should be a valid pointer to an I2C handle opened with i2c_open().
The periphery I2C functions return 0 on success or one of the negative error codes below on failure.
The libc errno of the failure in an underlying libc library call can be obtained with the i2c_errno() helper function. A human readable error message can be obtained with the i2c_errmsg() helper function.
| Error Code | Description |
|---|---|
I2C_ERROR_ARG |
Invalid arguments |
I2C_ERROR_OPEN |
Opening I2C device |
I2C_ERROR_QUERY |
Querying I2C device attribtues |
I2C_ERROR_NOT_SUPPORTED |
I2C not supported on this device |
I2C_ERROR_TRANSFER |
I2C transfer |
I2C_ERROR_CLOSE |
Closing I2C device |
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include "i2c.h"
#define EEPROM_I2C_ADDR 0x50
int main(void) {
i2c_t *i2c;
i2c = i2c_new();
/* Open the i2c-0 bus */
if (i2c_open(i2c, "/dev/i2c-0") < 0) {
fprintf(stderr, "i2c_open(): %s\n", i2c_errmsg(i2c));
exit(1);
}
/* Read byte at address 0x100 of EEPROM */
uint8_t msg_addr[2] = { 0x01, 0x00 };
uint8_t msg_data[1] = { 0xff, };
struct i2c_msg msgs[2] =
{
/* Write 16-bit address */
{ .addr = EEPROM_I2C_ADDR, .flags = 0, .len = 2, .buf = msg_addr },
/* Read 8-bit data */
{ .addr = EEPROM_I2C_ADDR, .flags = I2C_M_RD, .len = 1, .buf = msg_data},
};
/* Transfer a transaction with two I2C messages */
if (i2c_transfer(i2c, msgs, 2) < 0) {
fprintf(stderr, "i2c_transfer(): %s\n", i2c_errmsg(i2c));
exit(1);
}
printf("0x%02x%02x: %02x\n", msg_addr[0], msg_addr[1], msg_data[0]);
i2c_close(i2c);
i2c_free(i2c);
return 0;
}