IIC_ACQUIRE_BUS(9) | Kernel Developer's Manual | IIC_ACQUIRE_BUS(9) |
iic_acquire_bus
,
iic_release_bus
, iic_exec
,
iic_smbus_write_byte
,
iic_smbus_read_byte
,
iic_smbus_receive_byte
—
Inter IC (I2C) bus
#include
<dev/i2c/i2cvar.h>
int
iic_acquire_bus
(i2c_tag_t ic,
int flags);
int
iic_release_bus
(i2c_tag_t ic,
int flags);
int
iic_exec
(i2c_tag_t ic,
i2c_op_t op, i2c_addr_t addr,
const void *cmdbuf, size_t
cmdlen, void *buf, size_t
len, int flags);
int
iic_smbus_write_byte
(i2c_tag_t
ic, i2c_addr_t addr, uint8_t
cmd, uint8_t data, int
flags);
int
iic_smbus_read_byte
(i2c_tag_t
ic, i2c_addr_t addr, uint8_t
cmd, uint8_t *datap, int
flags);
int
iic_smbus_receive_byte
(i2c_tag_t
ic, i2c_addr_t addr, uint8_t
*datap, int flags);
I2C is a two-wire bus developed by Philips used for connecting
integrated circuits. It is commonly used for connecting devices such as
EEPROMs, temperature sensors, fan controllers, real-time clocks, tuners, and
other types of integrated circuits. The iic
interface provides a means of communicating with I2C-connected devices. The
System Management Bus, or SMBus, is a variant of the I2C bus with a
simplified command protocol and some electrical differences.
Drivers for devices attached to the I2C bus will make use of the following data types:
struct i2c_attach_args { i2c_tag_t ia_tag; /* controller */ i2c_addr_t ia_addr; /* address of device */ int ia_size; /* size (for EEPROMs) */ char *ia_name; /* chip name */ void *ia_cookie; /* pass extra info from bus to dev */ };
The following functions comprise the API provided to drivers of I2C-connected devices:
iic_acquire_bus
(ic,
flags)iic_acquire_bus
() that sleeping is not
permitted.iic_release_bus
(ic,
flags)iic_acquire_bus
(), it must also be passed to
iic_release_bus
().iic_exec
(ic,
op, addr,
cmdbuf, cmdlen,
buf, len,
flags);iic_exec
() initiates the operation by sending a
START condition on the I2C bus and then transmitting the address of the
target device along with the transaction type. If
cmdlen is non-zero, the command pointed to by
cmdbuf is then sent to the device. If
buflen is non-zero,
iic_exec
() will then transmit or receive the data,
as indicated by op. If op
indicates a read operation, iic_exec
() will send a
REPEATED START before transferring the data. If op
so indicates, a STOP condition will be sent on the I2C bus at the
conclusion of the operation. Passing the I2C_F_POLL
flag indicates to iic_exec
() that sleeping is not
permitted.iic_smbus_write_byte
(ic,
addr, cmd,
data, flags)iic_smbus_read_byte
(ic,
addr, cmd,
datap, flags)iic_smbus_receive_byte
(ic,
addr, datap,
flags)The I2C controller driver must fill in the function pointers of an i2c_controller structure, which is defined as follows:
struct i2c_controller { void *ic_cookie; /* controller private */ int (*ic_acquire_bus)(void *, int); void (*ic_release_bus)(void *, int); int (*ic_exec)(void *, i2c_op_t, i2c_addr_t, const void *, size_t, void *, size_t, int); int (*ic_send_start)(void *, int); int (*ic_send_stop)(void *, int); int (*ic_initiate_xfer)(void *, i2c_addr_t, int); int (*ic_read_byte)(void *, uint8_t *, int); int (*ic_write_byte)(void *, uint8_t, int); };
The (*ic_acquire_bus)
() and
(*ic_release_bus)
() functions must always be
provided.
The controller driver may elect to provide an
(*ic_exec)
() function. This function is intended for
use by automated controllers that do not provide manual control over I2C bus
conditions such as START and STOP.
If the (*ic_exec)
() function is not
provided, the following 5 functions will be used by
iic_exec
() in order to execute the I2C bus
operation:
(*ic_send_start)
(cookie,
flags)(*ic_send_stop)
(cookie,
flags)(*ic_initiate_xfer)
(cookie,
addr, flags)ETIMEDOUT
should be
returned if a timeout that would indicate that the device is not present
occurs.(*ic_read_byte)
(cookie,
datap, flags)(*ic_write_byte)
(cookie,
data, flags)The iic
API first appeared in
NetBSD 2.0. OpenBSD support
was added in OpenBSD 3.6.
The iic
API was written by Steve C.
Woodford and Jason R. Thorpe for NetBSD and then
ported to OpenBSD by Alexander
Yurchenko
<grange@openbsd.org>.
November 23, 2015 | OpenBSD-current |