IIO Dummy Experiment Three: Play with IIO Generic Buffers and Trigger

26 Feb 2017

This experiment is the last part of the series that uses Daniel’s tasks [1] as a study guide for IIO subsystem. We provided the following posts:

The experiment described in this here aims to accomplish the following tasks:

Load the hrtimer software trigger;
Create a trigger using configfs;
Inspect /sys/bus/iio/;
Compile and use iio_generic_buffer;

At this moment, I suppose that you are comfortable with compile, load/unload, and know a little about /sys/bus/iio. This post intends to be straightforward because I presume you already read the previous post or have a good experience with this kind of tasks.

Load and unload `hrtimer`

We begin this experiment with the load of the required modules. Before you try to load the iio-trig-hrtimer module, check if you have the iio-trig-hrtimer in your system as follows:

$ modinfo iio-trig-hrtimer
filename:       /lib/modules/4.16.0-rc4-TORVALDS+/kernel/drivers/iio/trigger/iio-trig-hrtimer.ko.xz
license:        GPL v2
description:    Periodic hrtimer trigger for the IIO subsystem
author:         Daniel Baluta <daniel.baluta@intel.com>
author:         Marten Svanfeldt <marten@intuitiveaerial.com>
srcversion:     F98F2B7577CDE7CC414F0A4
depends:        industrialio-sw-trigger,industrialio
retpoline:      Y
intree:         Y
name:           iio_trig_hrtimer
vermagic:       4.16.0-rc4-TORVALDS+ SMP preempt mod_unload modversions

In my particular case, I usually use a customize kernel version and sometimes I have to configure and compile a specific module manually. If you want to enable the iio-trig-* follows the step in Figure 1.

Finally, load iio-trig-hrtimer and iio_dummy:

$ sudo modprobe iio-trig-hrtimer
$ sudo modprobe iio_dummy

Create a trigger with `configfs`

You already know the configfs filesystem from the previous posts. Now, we want to use it for creating a trigger named t1.

sudo mkdir /mnt/iio_experiments/
sudo mount -t configfs none /mnt/iio_experiments/
sudo mkdir /mnt/iio_experiments/iio/triggers/hrtimer/t1
sudo mkdir /mnt/iio_experiments/iio/devices/dummy/iio_test/

Now, look at /sys/bus/iio/devices/:

$ ls /sys/bus/iio/devices/
iio:device0  iio_evgen  trigger0

$ ls /sys/bus/iio/devices/trigger0
name  power  sampling_frequency  subsystem  uevent

Notice, the directory trigger0 and the elements inside it. You will see that our t1 trigger is finally created.

Compile and using `iio_generic_buffer`

Compile tools from tools/iio directory with the following command:

make -C tools/iio

Now, let’s just look at the iio_generic_buffer options with the command:

$ ./tools/iio/iio_generic_buffer -h
./tools/iio/iio_generic_buffer: invalid option -- 'h'
Usage: generic_buffer [options]...
Capture, convert and output data from IIO device buffer
  -a         Auto-activate all available channels
  -A         Force-activate ALL channels
  -c <n>     Do n conversions
  -e         Disable wait for event (new data)
  -g         Use trigger-less mode
  -l <n>     Set buffer length to n samples
  --device-name -n <name>
  --device-num -N <num>
        Set device by name or number (mandatory)
  --trigger-name -t <name>
  --trigger-num -T <num>
        Set trigger by name or number
  -w <n>     Set delay between reads in us (event-less mode)

There are many interesting options, however, for this tutorial we are interested in only two of them: -n and -t. So, let’s try to see what happens during the command execution:

[root@atma]# ./tools/iio/iio_generic_buffer -n iio_test -t t1
iio device number being used is 0
iio trigger number being used is 0
No channels are enabled, we have nothing to scan.
Enable channels manually in /sys/bus/iio/devices/iio:device0/scan_elements/*_en or pass -a to autoenable channels and try again.

Ooops… It does not work as expected, no problem! The output message is very informative. We forgot to enable the channel; we can just use the -a option. Let’s try:

[root@atma]# ./tools/iio/iio_generic_buffer -a -n iio_test -t t1
iio device number being used is 0
iio trigger number being used is 0
Enabling all channels
Enabling: in_voltage3-voltage4_en
Enabling: in_accel_x_en
Enabling: in_voltage1-voltage2_en
Enabling: in_timestamp_en
Enabling: in_voltage0_en
/sys/bus/iio/devices/iio:device0 t1
0.018662 -0.000044 -0.000003 344.000000 1520363584895707167 
0.018662 -0.000044 -0.000003 344.000000 1520363584905685726 
Disabling: in_voltage3-voltage4_en
Disabling: in_accel_x_en
Disabling: in_voltage1-voltage2_en
Disabling: in_timestamp_en
Disabling: in_voltage0_en

References

IIO tasks proposed by Daniel Baluta
tools/iio/iio_event_monitor.c the source code has many useful comments.
The iio_simple_dummy_event Events Anatomy

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IIO Dummy Experiment Three: Play with IIO Generic Buffers and Trigger

Load and unload hrtimer

Create a trigger with configfs

Compile and using iio_generic_buffer

References

Load and unload `hrtimer`

Create a trigger with `configfs`

Compile and using `iio_generic_buffer`