NAME¶
iic
—
I2C generic I/O device driver
SYNOPSIS¶
device iic
#include
<dev/iicbus/iic.h>
DESCRIPTION¶
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.
SEE ALSO¶
ioctl(2),
read(2),
write(2),
iicbus(4)
HISTORY¶
The
iic
manual page first appeared in
FreeBSD 3.0.
AUTHORS¶
This manual page was written by
Nicolas
Souchu and
M. Warner Losh.
BUGS¶
Only the
I2CRDWR
ioctl(2) is thread safe. All other interfaces
suffer from some kind of race.