a476ba06d5
o Remove All Rights Reserved from my notices o imp@FreeBSD.org everywhere o regularize punctiation, eliminate date ranges o Make sure that it's clear that I don't claim All Rights reserved by listing All Rights Reserved on same line as other copyright holders (but not me). Other such holders are also listed last where it's clear.
260 lines
6.9 KiB
Groff
260 lines
6.9 KiB
Groff
.\" Copyright (c) 1998, Nicolas Souchu All rights reserved.
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.\" Copyright (c) 2006 M. Warner Losh <imp@FreeBSD.org>
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 15, 2015
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.Dt IIC 4
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.Os
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.Sh NAME
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.Nm iic
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.Nd I2C generic I/O device driver
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.Sh SYNOPSIS
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.Cd "device iic"
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.Pp
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.In dev/iicbus/iic.h
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.Sh DESCRIPTION
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The
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.Nm
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device driver provides generic I/O to any
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.Xr iicbus 4
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instance.
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In order to control I2C devices, use
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.Pa /dev/iic?
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with the
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following ioctls:
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.Bl -tag -width ".Dv I2CRPTSTART"
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.It Dv I2CSTART
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.Pq Vt "struct iiccmd"
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Sends the start condition to the slave specified by the
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.Va slave
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element to the bus.
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The
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.Va slave
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element consists of a 7-bit address and a read/write bit
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(that is, a 7-bit address << 1 | r/w).
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A read operation is initiated when the read/write bit is set, or a write
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operation when it is cleared.
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All other elements are ignored.
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If successful, the file descriptor receives exclusive
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ownership of the underlying iicbus instance.
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.It Dv I2CRPTSTART
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.Pq Vt "struct iiccmd"
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Sends the repeated start condition to the slave specified by the
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.Va slave
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element to the bus.
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The slave address should be specified as in
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.Dv I2CSTART .
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All other elements are ignored.
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.Dv I2CSTART
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must have previously been issued on the same file descriptor.
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.It Dv I2CSTOP
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No argument is passed.
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Sends the stop condition to the bus.
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If
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.Dv I2CSTART
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was previously issued on the file descriptor, the current transaction is
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terminated and exclusive ownership of the underlying iicbus instance is
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released.
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Otherwise, no action is performed.
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.It Dv I2CRSTCARD
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.Pq Vt "struct iiccmd"
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Resets the bus.
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The argument is completely ignored.
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This command does not require
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.Dv I2CSTART
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to have been previously issued on the file descriptor.
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If it was previously issued, exclusive ownership of the underlying iicbus
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instance is released.
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.It Dv I2CWRITE
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.Pq Vt "struct iiccmd"
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Writes data to the
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.Xr iicbus 4 .
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The bus must already be started by a previous
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.Dv I2CSTART
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on the file descriptor.
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The
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.Va slave
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element is ignored.
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The
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.Va count
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element is the number of bytes to write.
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The
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.Va last
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element is a boolean flag.
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It must be zero when additional read commands will follow, or non-zero if this
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is the last command.
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The
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.Va buf
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element is a pointer to the data to write to the bus.
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.It Dv I2CREAD
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.Pq Vt "struct iiccmd"
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Reads data from the
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.Xr iicbus 4 .
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The bus must already be started by a previous
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.Dv I2CSTART
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on the file descriptor.
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The
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.Va slave
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element is ignored.
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The
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.Va count
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element is the number of bytes to read.
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The
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.Va last
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element is a boolean flag.
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It must be zero when additional read commands will follow, or non-zero if this
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is the last command.
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The
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.Va buf
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element is a pointer to where to store the data read from the bus.
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Short reads on the bus produce undefined results.
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.It Dv I2CRDWR
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.Pq Vt "struct iic_rdwr_data"
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Generic read/write interface.
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Allows for an arbitrary number of commands to be sent to
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an arbitrary number of devices on the bus.
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Any previous transaction started by
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.Dv I2CSTART
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must be terminated by
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.Dv I2CSTOP
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or
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.Dv I2CRSTCARD
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before
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.Dv I2CRDWR
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can be issued on the same file descriptor.
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A read transfer is specified if
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.Dv IIC_M_RD
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is set in
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.Va flags .
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Otherwise the transfer is a write transfer.
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The
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.Va slave
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element specifies the 7-bit address with the read/write bit for the transfer.
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The read/write bit will be handled by the iicbus stack based on the specified
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transfer operation.
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The
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.Va len
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element is the number of
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.Pq Vt "struct iic_msg"
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messages encoded on
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.Pq Vt "struct iic_rdwr_data" .
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The
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.Va buf
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element is a buffer for that data.
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This ioctl is intended to be
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.Tn Linux
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compatible.
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.It Dv I2CSADDR
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.Pq Vt "uint8_t"
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Associate the specified address with the file descriptor for use by
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subsequent
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.Xr read 2
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or
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.Xr write 2
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calls.
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The argument is an 8-bit address (that is, a 7-bit address << 1).
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The read/write bit in the least-significant position is ignored.
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Any subsequent read or write operation will set or clear that bit as needed.
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.El
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.Pp
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The following data structures are defined in
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.In dev/iicbus/iic.h
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and referenced above:
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.Bd -literal -offset indent
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struct iiccmd {
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u_char slave;
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int count;
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int last;
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char *buf;
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};
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/* Designed to be compatible with linux's struct i2c_msg */
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struct iic_msg
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{
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uint16_t slave;
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uint16_t flags;
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#define IIC_M_WR 0 /* Fake flag for write */
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#define IIC_M_RD 0x0001 /* read vs write */
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#define IIC_M_NOSTOP 0x0002 /* do not send a I2C stop after message */
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#define IIC_M_NOSTART 0x0004 /* do not send a I2C start before message */
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uint16_t len; /* msg length */
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uint8_t * buf;
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};
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struct iic_rdwr_data {
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struct iic_msg *msgs;
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uint32_t nmsgs;
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};
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.Ed
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.Pp
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It is also possible to use
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.Xr read 2
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or
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.Xr write 2 ,
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in which case the I2C start/stop handshake is managed by
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.Xr iicbus 4 .
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The address used for the read/write operation is the one passed to the most
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recent
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.Dv I2CSTART
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.Xr ioctl 2
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or
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.Dv I2CSADDR
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.Xr ioctl 2
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on the open
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.Pa /dev/iic?
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file descriptor.
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Closing the file descriptor clears any addressing state established by a
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previous
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.Dv I2CSTART
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or
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.Dv I2CSADDR ,
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stops any transaction established by a not-yet-terminated
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.Dv I2CSTART ,
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and releases iicbus ownership.
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Because addressing state is stored on a per-file-descriptor basis, it is
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permissible for multiple file descriptors to be simultaneously open on the
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same
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.Pa /dev/iic?
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device.
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Concurrent transactions on those descriptors are synchronized by the
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exclusive-ownership requests issued to the underlying iicbus instance.
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.Sh SEE ALSO
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.Xr ioctl 2 ,
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.Xr read 2 ,
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.Xr write 2 ,
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.Xr iicbus 4
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.Sh HISTORY
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The
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.Nm
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manual page first appeared in
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.Fx 3.0 .
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.Sh AUTHORS
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.An -nosplit
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This
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manual page was written by
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.An Nicolas Souchu
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and
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.An M. Warner Losh .
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