.\" $OpenBSD: iic.9,v 1.6 2007/05/31 19:20:00 jmc Exp $ .\" .\" Copyright (c) 2003 Wasabi Systems, Inc. .\" All rights reserved. .\" .\" Written by Jason R. Thorpe for Wasabi Systems, Inc. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed for the NetBSD Project by .\" Wasabi Systems, Inc. .\" 4. The name of Wasabi Systems, Inc. may not be used to endorse .\" or promote products derived from this software without specific prior .\" written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY WASABI SYSTEMS, INC. ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED .\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL WASABI SYSTEMS, INC .\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS .\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN .\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE .\" POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: May 31 2007 $ .Dt IIC 9 .Os .Sh NAME .Nm iic_acquire_bus , .Nm iic_release_bus , .Nm iic_exec , .Nm iic_smbus_write_byte , .Nm iic_smbus_read_byte , .Nm iic_smbus_receive_byte .Nd Inter IC (I2C) bus .Sh SYNOPSIS .Fd #include .Ft int .Fo iic_acquire_bus .Fa "i2c_tag_t ic" .Fa "int flags" .Fc .Ft int .Fo iic_release_bus .Fa "i2c_tag_t ic" .Fa "int flags" .Fc .Ft int .Fo iic_exec .Fa "i2c_tag_t ic" .Fa "i2c_op_t op" .Fa "i2c_addr_t addr" .Fa "const void *cmdbuf" .Fa "size_t cmdlen" .Fa "void *buf" .Fa "size_t len" .Fa "int flags" .Fc .Ft int .Fo iic_smbus_write_byte .Fa "i2c_tag_t ic" .Fa "i2c_addr_t addr" .Fa "uint8_t cmd" .Fa "uint8_t data" .Fa "int flags" .Fc .Ft int .Fo iic_smbus_read_byte .Fa "i2c_tag_t ic" .Fa "i2c_addr_t addr" .Fa "uint8_t cmd" .Fa "uint8_t *datap" .Fa "int flags" .Fc .Ft int .Fo iic_smbus_receive_byte .Fa "i2c_tag_t ic" .Fa "i2c_addr_t addr" .Fa "uint8_t *datap" .Fa "int flags" .Fc .Sh 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 .Nm 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. .Sh DATA TYPES Drivers for devices attached to the I2C bus will make use of the following data types: .Bl -tag -width i2c_addr_t .It Fa i2c_tag_t Controller tag for the I2C bus. This is a pointer to a .Fa struct i2c_controller , consisting of function pointers filled in by the I2C controller driver. .It Fa i2c_op_t I2C bus operation. The following I2C bus operations are defined: .Bl -tag -width XXXX .It I2C_OP_READ Perform a read operation. .It I2C_OP_READ_WITH_STOP Perform a read operation and send a STOP condition on the I2C bus at the conclusion of the read. .It I2C_OP_WRITE Perform a write operation. .It I2C_OP_WRITE_WITH_STOP Perform a write operation and send a STOP condition on the I2C bus at the conclusion of the write. .El .It Fa i2c_addr_t I2C device address. .It Fa struct i2c_attach_args Devices are attached to an I2C bus using this structure. The structure is defined as follows: .Bd -literal 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 */ }; .Ed .El .Sh FUNCTIONS The following functions comprise the API provided to drivers of I2C-connected devices: .Bl -tag -width iic_exec .It Fn 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 operations necessary, and then release the bus lock. Passing the .Fa I2C_F_POLL flag indicates to .Fn iic_acquire_bus that sleeping is not permitted. .It Fn iic_release_bus "ic" "flags" Release an exclusive lock on the I2C bus. If the .Fa I2C_F_POLL flag was passed to .Fn iic_acquire_bus , it must also be passed to .Fn iic_release_bus . .It Xo .Fo iic_exec .Fa "ic" .Fa "op" .Fa "addr" .Fa "cmdbuf" .Fa "cmdlen" .Fa "buf" .Fa "len" .Fa "flags" .Fc .Xc Perform a series of I2C transactions on the bus. .Fn 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 .Fa cmdlen is non-zero, the command pointed to by .Fa cmdbuf is then sent to the device. If .Fa buflen is non-zero, .Fn iic_exec will then transmit or receive the data, as indicated by .Fa op . If .Fa op indicates a read operation, .Fn iic_exec will send a REPEATED START before transferring the data. If .Fa op so indicates, a STOP condition will be sent on the I2C bus at the conclusion of the operation. Passing the .Fa I2C_F_POLL flag indicates to .Fn iic_exec that sleeping is not permitted. .It Fn 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 .Fa cmdlen of 1 and .Fa len of 1. .It Fn 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 .Fa cmdlen of 1 and .Fa len of 1. .It Fn iic_smbus_receive_byte "ic" "addr" "datap" "flags" Perform an SMBus RECEIVE BYTE operation. This is equivalent to I2C_OP_READ_WITH_STOP with .Fa cmdlen of 0 and .Fa len of 1. .El .Sh CONTROLLER INTERFACE The I2C controller driver must fill in the function pointers of an .Fa i2c_controller structure, which is defined as follows: .Bd -literal 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); }; .Ed .Pp The .Fn (*ic_acquire_bus) and .Fn (*ic_release_bus) functions must always be provided. .Pp The controller driver may elect to provide an .Fn (*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. .Pp If the .Fn (*ic_exec) function is not provided, the following 5 functions will be used by .Fn iic_exec in order to execute the I2C bus operation: .Bl -tag -width XXXX .It Fn (*ic_send_start) "cookie" "flags" Send a START condition on the I2C bus. The .Fa I2C_F_POLL flag indicates that sleeping is not permitted. .It Fn (*ic_send_stop) "cookie" "flags" Send a STOP condition on the I2C bus. The .Fa I2C_F_POLL flag indicates that sleeping is not permitted. .It Fn (*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 .Fa I2C_F_READ flag indicates a read transfer; the lack of this flag indicates a write transfer. The .Fa I2C_F_POLL flag indicates that sleeping is not permitted. The error code .Dv ETIMEDOUT should be returned if a timeout that would indicate that the device is not present occurs. .It Fn (*ic_read_byte) "cookie" "datap" "flags" Read a byte from the I2C bus into the memory location referenced by .Fa datap . The .Fa 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 .Fa I2C_F_STOP flag indicates that a STOP condition should be sent on the I2C bus following the transfer of the byte. The .Fa I2C_F_POLL flag indicates that sleeping is not permitted. .It Fn (*ic_write_byte) "cookie" "data" "flags" Write the byte contained in .Fa data to the I2C bus. The .Fa I2C_F_STOP flag indicates that a STOP condition should be sent on the I2C bus following the transfer of the byte. The .Fa I2C_F_POLL flag indicates that sleeping is not permitted. .El .Sh SEE ALSO .Xr iic 4 .Sh HISTORY The .Nm iic API first appeared in .Nx 2.0 . .Ox support was added in .Ox 3.6 . .Sh AUTHORS The .Nm iic API was written by Steve C. Woodford and Jason R. Thorpe for .Nx and then ported to .Ox by .An Alexander Yurchenko Aq grange@openbsd.org .