IIC(9) BSD Kernel Developer's Manual IIC(9)NAME
iic_acquire_bus, iic_release_bus, iic_exec, iic_smbus_write_byte,
iic_smbus_read_byte, iic_smbus_receive_byte — Inter IC (I2C) bus
SYNOPSIS
#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 buflen, 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);
DESCRIPTION
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 com‐
municating 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.
DATA TYPES
Drivers for devices attached to the I2C bus will make use of the follow‐
ing data types:
i2c_tag_t Controller tag for the I2C bus. This is a pointer to a
struct i2c_controller, consisting of function pointers filled
in by the I2C controller driver.
i2c_op_t I2C bus operation. The following I2C bus operations are
defined:
I2C_OP_READ
Perform a read operation.
I2C_OP_READ_WITH_STOP
Perform a read operation and send a STOP condition on
the I2C bus at the conclusion of the read.
I2C_OP_WRITE
Perform a write operation.
I2C_OP_WRITE_WITH_STOP
Perform a write operation and send a STOP condition on
the I2C bus at the conclusion of the write.
i2c_addr_t I2C device address.
struct i2c_attach_args
Devices are attached to an I2C bus using this structure. The
structure is defined as follows:
struct i2c_attach_args {
i2c_tag_t ia_tag; /* controller */
i2c_addr_t ia_addr; /* address of device */
int ia_size; /* size (for EEPROMs) */
};
FUNCTIONS
The following functions comprise the API provided to drivers of I2C-con‐
nected devices:
iic_acquire_bus(ic, flags)
Acquire an exclusive lock on the I2C bus. This is required
since only one device may communicate on the I2C bus at a time.
Drivers should acquire the bus lock, perform the I2C bus opera‐
tions necessary, and then release the bus lock. Passing the
I2C_F_POLL flag indicates to iic_acquire_bus() that sleeping is
not permitted.
iic_release_bus(ic, flags)
Release an exclusive lock on the I2C bus. If the I2C_F_POLL
flag was passed to iic_acquire_bus(), it must also be passed to
iic_release_bus().
iic_exec(ic, op, addr, cmdbuf, cmdlen, buf, buflen, flags)
Perform a series of I2C transactions on the bus. 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 opera‐
tion, 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)
Perform an SMBus WRITE BYTE operation. This is equivalent to
I2C_OP_WRITE_WITH_STOP with cmdlen of 1 and buflen of 1.
iic_smbus_read_byte(ic, addr, cmd, datap, flags)
Perform an SMBus READ BYTE operation. This is equivalent to
I2C_OP_READ_WITH_STOP with cmdlen of 1 and buflen of 1.
iic_smbus_receive_byte(ic, addr, datap, flags)
Perform an SMBus RECEIVE BYTE operation. This is equivalent to
I2C_OP_READ_WITH_STOP with cmdlen of 0 and buflen of 1.
CONTROLLER INTERFACE
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)
Send a START condition on the I2C bus. The I2C_F_POLL flag indi‐
cates that sleeping is not permitted.
(*ic_send_stop)(cookie, flags)
Send a STOP condition on the I2C bus. The I2C_F_POLL flag indi‐
cates that sleeping is not permitted.
(*ic_initiate_xfer)(cookie, addr, flags)
Initiate a transfer on the I2C bus by sending a START condition and
then transmitting the I2C device address and transfer type. The
I2C_F_READ flag indicates a read transfer; the lack of this flag
indicates a write transfer. The I2C_F_POLL flag indicates that
sleeping is not permitted. The error code ETIMEDOUT should be
returned if a timeout that would indicate that the device is not
present occurs.
(*ic_read_byte)(cookie, datap, flags)
Read a byte from the I2C bus into the memory location referenced by
datap. The I2C_F_LAST flag indicates that this is the final byte
of the transfer, and that a NACK condition should be sent on the
I2C bus following the transfer of the byte. The I2C_F_STOP flag
indicates that a STOP condition should be sent on the I2C bus fol‐
lowing the transfer of the byte. The I2C_F_POLL flag indicates
that sleeping is not permitted.
(*ic_write_byte)(cookie, data, flags)
Write the byte contained in data to the I2C bus. The I2C_F_STOP
flag indicates that a STOP condition should be sent on the I2C bus
following the transfer of the byte. The I2C_F_POLL flag indicates
that sleeping is not permitted.
SEE ALSOiic(4), i2cscan(8)
NXP Semiconductors, I2C-bus Specification and User Manual, Revision 03,
http://www.ics.nxp.com/support/documents/i2c/pdf/i2c.bus.specification.pdf,
June 19, 2007.
Duracell Inc. et. al., System Management Bus (SMBus) Specification,
Version 2.0, http://smbus.org/specs/smbus20.pdf, August 3, 2000.
HISTORY
The iic API first appeared in NetBSD 2.0. OpenBSD support was added in
OpenBSD 3.6.
AUTHORS
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⟩.
BSD October 15, 2011 BSD
