iic

device iic

#include <dev/iicbus/iic.h>

The iic device driver provides generic I/O to any iicbus(4) instance. In order to control I2C devices, use /dev/iic? with the following ioctls:

I2CSTART

(struct iiccmd) Sends the start condition to the slave specified by the slave element to the bus. The slave element consists of a 7-bit address and a read/write bit (i.e., 7-bit address << 1 | r/w). If the read/write bit is set a read operation is initiated, if the read/write bit is cleared a write operation is initiated. All other elements are ignored.

I2CRPTSTART

(struct iiccmd) Sends the repeated start condition to the slave specified by the slave element to the bus. The slave address should be specified as in I2CSTART. All other elements are ignored.

I2CSTOP

No argument is passed. Sends the stop condition to the bus. This terminates the current transaction.

I2CRSTCARD

(struct iiccmd) Resets the bus. The argument is completely ignored.

I2CWRITE

(struct iiccmd) Writes data to the iicbus(4). The bus should already be started. The slave element is ignored. The count element is the number of bytes to write. The last element is a boolean flag. It is non-zero when additional write commands will follow. The buf element is a pointer to the data to write to the bus.

I2CREAD

(struct iiccmd) Reads data from the iicbus(4). The bus should already be started. The slave element is ignored. The count element is the number of bytes to write. The last element is a boolean flag. It is non-zero when additional write commands will follow. The buf element is a pointer to where to store the data read from the bus. Short reads on the bus produce undefined results.

I2CRDWR

(struct iic_rdwr_data) Generic read/write interface. Allows for an arbitrary number of commands to be sent to an arbitrary number of devices on the bus. A read transfer is specified if IIC_M_RD is set in flags. Otherwise the transfer is a write transfer. The slave element specifies the 7-bit address with the read/write bit for the transfer. The read/write bit will be handled by the iicbus stack based on the specified transfer operation. The len element is the number of (struct iic_msg) messages encoded on (struct iic_rdwr_data). The buf element is a buffer for that data. This ioctl is intended to be Linux compatible.

The following data structures are defined in <dev/iicbus/iic.h> and referenced above:

struct iiccmd {
	u_char slave;
	int count;
	int last;
	char *buf;
};

/* Designed to be compatible with linux's struct i2c_msg */
struct iic_msg
{
	uint16_t	slave;
	uint16_t	flags;
#define IIC_M_RD	0x0001	/* read vs write */
	uint16_t	len;	/* msg length */
	uint8_t *	buf;
};

struct iic_rdwr_data {
	struct iic_msg *msgs;
	uint32_t nmsgs;
};

It is also possible to use read/write routines, then I2C start/stop handshake is managed by the iicbus(4) system. However, the address used for the read/write routines is the one passed to last I2CSTART ioctl(2) to this device.

ioctl(2), read(2), write(2), iicbus(4)

The iic manual page first appeared in FreeBSD 3.0.

This manual page was written by Nicolas Souchu and M. Warner Losh.

Only the I2CRDWR ioctl(2) is thread safe. All other interfaces suffer from some kind of race.