.. SPDX-License-Identifier: GPL-2.0
|
|
================================
|
Linux I2C slave testunit backend
|
================================
|
|
by Wolfram Sang <wsa@sang-engineering.com> in 2020
|
|
This backend can be used to trigger test cases for I2C bus masters which
|
require a remote device with certain capabilities (and which are usually not so
|
easy to obtain). Examples include multi-master testing, and SMBus Host Notify
|
testing. For some tests, the I2C slave controller must be able to switch
|
between master and slave mode because it needs to send data, too.
|
|
Note that this is a device for testing and debugging. It should not be enabled
|
in a production build. And while there is some versioning and we try hard to
|
keep backward compatibility, there is no stable ABI guaranteed!
|
|
Instantiating the device is regular. Example for bus 0, address 0x30:
|
|
# echo "slave-testunit 0x1030" > /sys/bus/i2c/devices/i2c-0/new_device
|
|
After that, you will have a write-only device listening. Reads will just return
|
an 8-bit version number of the testunit. When writing, the device consists of 4
|
8-bit registers and all must be written to start a testcase, i.e. you must
|
always write 4 bytes to the device. The registers are:
|
|
0x00 CMD - which test to trigger
|
0x01 DATAL - configuration byte 1 for the test
|
0x02 DATAH - configuration byte 2 for the test
|
0x03 DELAY - delay in n * 10ms until test is started
|
|
Using 'i2cset' from the i2c-tools package, the generic command looks like:
|
|
# i2cset -y <bus_num> <testunit_address> <CMD> <DATAL> <DATAH> <DELAY> i
|
|
DELAY is a generic parameter which will delay the execution of the test in CMD.
|
While a command is running (including the delay), new commands will not be
|
acknowledged. You need to wait until the old one is completed.
|
|
The commands are described in the following section. An invalid command will
|
result in the transfer not being acknowledged.
|
|
Commands
|
--------
|
|
0x00 NOOP (reserved for future use)
|
|
0x01 READ_BYTES (also needs master mode)
|
DATAL - address to read data from (lower 7 bits, highest bit currently unused)
|
DATAH - number of bytes to read
|
|
This is useful to test if your bus master driver is handling multi-master
|
correctly. You can trigger the testunit to read bytes from another device on
|
the bus. If the bus master under test also wants to access the bus at the same
|
time, the bus will be busy. Example to read 128 bytes from device 0x50 after
|
50ms of delay:
|
|
# i2cset -y 0 0x30 0x01 0x50 0x80 0x05 i
|
|
0x02 SMBUS_HOST_NOTIFY (also needs master mode)
|
DATAL - low byte of the status word to send
|
DATAH - high byte of the status word to send
|
|
This test will send an SMBUS_HOST_NOTIFY message to the host. Note that the
|
status word is currently ignored in the Linux Kernel. Example to send a
|
notification after 10ms:
|
|
# i2cset -y 0 0x30 0x02 0x42 0x64 0x01 i
|
