.TH I2C 3
.SH NAME
i2c \- basic I2C interface
.SH SYNOPSIS
.B bind -a
.BI #J n
.B /dev
.PP
.BI /dev/i2c. n .ctl
. br
.BI /dev/i2c. n .data
.fi
.SH DESCRIPTION
.I I2c
serves a one-level directory with two files
that give access to the target device with address
.I n
(given in hexadecimal)
on the system's I2C bus.
.I N
is usually determined by the I2C device manufacturer.
I2C gives address 0 special meaning as the `general call' address.
See an I2C specification for details.
.PP
The control file
.BI i2c. n .ctl
accepts commands to set the valid address range and
subaddressing mode for the corresponding data file.
The following control messages can be written to it:
.TP
.B a10
Force 10-bit addressing instead of 7-bit addressing.
Otherwise 10-bit addressing is used only if the device address
.I n
is bigger than 255.
.TP
.BI size " nbytes"
.br
Set the logical size of the target device to
.IR nbytes .
(By default when opened, it is 256 bytes, enough for most small I2C devices.)
IO requests will be kept within this limit.
This value is also returned by
.B Sys->stat
as the length of the data file.
.TP
.BI subaddress " \fR[\fP n \fR]\fP"
.br
Cause subsequent reads and writes
on the data file to use I2C subaddressing
with
.I n
byte subaddresses (default: 1 byte).
.I N
must be no larger than 4.
The target device must support subaddressing.
By default, the device is not subaddressed.
Setting
.I n
to zero switches off subaddressing.
.PP
When read,
the control file displays the current settings.
.PP
The data file
.BI i2c. n .data
can be read or written to
exchange data with the slave device with address
.I n
(where
.I n
is given in hexadecimal).
Each write request transmits the given data
to the device.
Each read request sends a receive
request to the device and returns the resulting data.
If the I2C target is subaddressed, the current file offset
is used as the subaddress;
otherwise the file offset is ignored, and the device typically starts at 0 for each transfer request.
Read and write requests are trimmed to the declared
size of the device.
.SH SOURCE
.B /sys/src/9/bcm/devi2c.c
.br
.B /sys/src/9/bcm/i2c.c