Plan 9 /sys/man/3/i2c

NAME

i2c – basic I2C interface

SYNOPSIS

bind –a #Jn /dev
/dev/i2c.n.ctl /dev/i2c.n.data

DESCRIPTION

I2c serves a one–level directory with two files that give access to the target device with address n (given in hexadecimal) on the system's I2C bus. 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.
The control file 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:
a10 Force 10–bit addressing instead of 7–bit addressing. Otherwise 10–bit addressing is used only if the device address n is bigger than 255.
size nbytes

Set the logical size of the target device to 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 Sys–>stat as the length of the data file.

subaddress [ n ]

Cause subsequent reads and writes on the data file to use I2C subaddressing with n byte subaddresses (default: 1 byte). N must be no larger than 4. The target device must support subaddressing. By default, the device is not subaddressed. Setting n to zero switches off subaddressing.

When read, the control file displays the current settings.
The data file i2c.n.data can be read or written to exchange data with the slave device with address n (where 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.


	`/sys/src/9/bcm/devi2c.c /sys/src/9/bcm/i2c.c`