Difference between revisions of "CL-SOM-iMX7: Linux: Debian"

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(→‎Bluez5 & PulseAudio)
Line 71: Line 71:
 
The Debian Linux image for CL-SOM-iMX7 includes all the information required to use Debian package management utilities.
 
The Debian Linux image for CL-SOM-iMX7 includes all the information required to use Debian package management utilities.
 
You can use [http://linux.die.net/man/8/apt-get apt-get] and [http://www.wlug.org.nz/dpkg(8) dpkg] out of the box.
 
You can use [http://linux.die.net/man/8/apt-get apt-get] and [http://www.wlug.org.nz/dpkg(8) dpkg] out of the box.
 +
 +
=== Analog Audio ===
 +
CL-SOM-iMX7 provides an analog audio interface, which is registered as a standard ALSA sound card.
 +
Use {{cmd|aplay -l}} to list all soundcards and digital audio devices registered on the system:
 +
<pre>
 +
root@cl-som-imx7-sid:~# aplay -l
 +
**** List of PLAYBACK Hardware Devices ****
 +
card 0: clsomimx7 [cl-som-imx7], device 0: 308a0000.sai-wm8731-hifi wm8731-hifi-0 []
 +
  Subdevices: 1/1
 +
  Subdevice #0: subdevice #0
 +
</pre>
 +
 +
==== Analog Audio Settings ====
 +
To enable the Analog audio playback, {{cmd|alsamixer}} or {{cmd|amixer}} applications can be used.
 +
* {{cmd|alsamixer}} - set the “''Output Mixer HiFi''” control on.
 +
or
 +
* {{cmd|amixer}} - set the “''Output Mixer HiFi Playback Switch''” control on using command line interface:
 +
<pre>
 +
root@cl-som-imx7-sid:~# amixer cset numid=14 1
 +
numid=14,iface=MIXER,name='Output Mixer HiFi Playback Switch'
 +
  ; type=BOOLEAN,access=rw------,values=1
 +
  : values=on
 +
</pre>
 +
 +
==== Analog Audio Playback ====
 +
In order to play back a sound file make use of the {{cmd|aplay}} application.
 +
<dl>
 +
* {{cmd|aplay -L}} can be used for listing of all pcm devices.
 +
</dl>
 +
Here is a sample output of {{cmd|aplay -L}} command:
 +
<pre>
 +
root@cl-som-imx7-sid:~# aplay -L
 +
null
 +
    Discard all samples (playback) or generate zero samples (capture)
 +
default:CARD=clsomimx7
 +
    cl-som-imx7,
 +
    Default Audio Device
 +
sysdefault:CARD=clsomimx7
 +
    cl-som-imx7,
 +
    Default Audio Device
 +
dmix:CARD=clsomimx7,DEV=0
 +
    cl-som-imx7,
 +
    Direct sample mixing device
 +
dsnoop:CARD=clsomimx7,DEV=0
 +
    cl-som-imx7,
 +
    Direct sample snooping device
 +
hw:CARD=clsomimx7,DEV=0
 +
    cl-som-imx7,
 +
    Direct hardware device without any conversions
 +
plughw:CARD=clsomimx7,DEV=0
 +
    cl-som-imx7,
 +
    Hardware device with all software conversions
 +
</pre>
 +
 +
The next command can be used for audio play back:
 +
<pre>
 +
root@cl-som-imx7-sid:~# aplay <wav-file>
 +
</pre>
 +
 +
==== Audio Input Settings ====
 +
CL-SOM-iMX7 provides an audio capturing feature from either ''Mic'' or ''Line In'' input sources.
 +
{{cmd|alsamixer}} or {{cmd|amixer}} can be used in order to switch between these inputs.
 +
===== Mic =====
 +
* {{cmd|alsamixer}}
 +
:: Capture Volume => 100
 +
:: Line Capture Switch => off
 +
:: Mic Capture Switch => on
 +
:: Input Mux => Mic
 +
* {{cmd|amixer}}
 +
<pre>
 +
amixer cset numid=3 31
 +
amixer cset numid=4 0
 +
amixer cset numid=6 1
 +
amixer cset numid=11 1
 +
</pre>
 +
===== Line In =====
 +
* {{cmd|alsamixer}}
 +
:: Capture Volume => 100
 +
:: Line Capture Switch => on
 +
:: Mic Capture Switch => off
 +
:: Input Mux => Line In
 +
* {{cmd|amixer}}
 +
<pre>
 +
amixer cset numid=3 31
 +
amixer cset numid=4 1
 +
amixer cset numid=6 0
 +
amixer cset numid=11 0
 +
</pre>
 +
 +
==== Sample Audio Recording ====
 +
As soon as the correct input values have been set, audio signal can be captured.
 +
Here is a sample command that shows the {{cmd|arecord}} usage for capturing audio signal from the selected input line.
 +
<pre>
 +
root@cl-som-imx7-sid:~# arecord -f dat -t wav /tmp/out.wav
 +
</pre>
  
 
=== USB On-The-Go (OTG) ===
 
=== USB On-The-Go (OTG) ===
Line 168: Line 263:
  
 
=== WiFi ===
 
=== WiFi ===
−
CL-SOM-iMX7 features 802.11b/g/n wireless connectivity solution, implemented with a TI WiLink8 Wireless controller module.
+
CL-SOM-iMX7 features 802.11b/g/n wireless connectivity solution, implemented with a TI WiLink8 Combo module.
  
 
==== WiFi Initialization ====
 
==== WiFi Initialization ====
Line 226: Line 321:
 
root@cl-som-imx7-sid:~# wpa_supplicant -B -Dwext -c /etc/wpa_supplicant.conf -i wlan0
 
root@cl-som-imx7-sid:~# wpa_supplicant -B -Dwext -c /etc/wpa_supplicant.conf -i wlan0
 
root@cl-som-imx7-sid:~# dhclient wlan0
 
root@cl-som-imx7-sid:~# dhclient wlan0
 +
</pre>
 +
 +
=== Bluetooth ===
 +
CL-SOM-iMX7 features Bluetooth 4.1 BLE interface, implemented with a TI WiLink8 Combo module.
 +
 +
==== Host Controller Interface (HCI) Initialization ====
 +
* HCI requires no user interaction for being configured. The driver gets loaded automatically unless this option has been disabled by putting a black list rule for this device.<br>
 +
Make sure that the Bluetooth driver is loaded:
 +
<pre>
 +
root@cl-som-imx7-sid:~# lsmod | grep btwilink
 +
btwilink                3822  0
 +
</pre>
 +
The Bluetooth driver can be loaded manually:
 +
<pre>
 +
root@cl-som-imx7-sid:~# modprobe btwilink
 +
</pre>
 +
 +
* HCI device configuration utility can be run to retrieve detailed information about the Bluetooth interfaces:
 +
<pre>
 +
root@cl-som-imx7-sid:~# hciconfig hci0 -a
 +
hci0:  Type: BR/EDR  Bus: UART
 +
        BD Address: 74:DA:EA:F9:CE:E3  ACL MTU: 1021:6  SCO MTU: 180:4
 +
        UP RUNNING
 +
        RX bytes:636 acl:0 sco:0 events:39 errors:0
 +
        TX bytes:1234 acl:0 sco:0 commands:39 errors:0
 +
        Features: 0xff 0xfe 0x2d 0xfe 0xdb 0xff 0x7b 0x87
 +
        Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3
 +
        Link policy: RSWITCH HOLD SNIFF
 +
        Link mode: SLAVE ACCEPT
 +
        Name: 'BlueZ 5.36'
 +
        Class: 0x000000
 +
        Service Classes: Unspecified
 +
        Device Class: Miscellaneous,
 +
        HCI Version: 4.1 (0x7)  Revision: 0x0
 +
        LMP Version: 4.1 (0x7)  Subversion: 0xac03
 +
        Manufacturer: Texas Instruments Inc. (13)
 +
</pre>
 +
 +
* If the HCI device is not running, use the below command to enable the HCI device:
 +
<pre>
 +
root@cl-som-imx7-sid:~# hciconfig hci0 up
 +
</pre>
 +
* HCI Inquire remote devices.
 +
<pre>
 +
root@cl-som-imx7-sid:~# hcitool scan
 +
Scanning ...
 +
</pre>
 +
 +
==== Bluez5 & PulseAudio ====
 +
Debian stretch/sid is using BlueZ 5 and PluseAudio 5, which are fairly new.<br>
 +
BlueZ 5 dropped support for alsa, so the solution for now is to use PulseAudio.<br>
 +
PulseAudio 5 only supports the A2DP profile and not HSP/HFP. <br>
 +
* Software to install {{filename|'''pulseaudio'''}}, {{filename|'''pulseaudio-module-bluetooth'''}}
 +
{{Note|{{filename|'''debian-image.tar.bz2'''}} has all these packages pre-installed. Continue to the [[#Start PulseAudio | Start PulseAudio]] section if you use this root filesystem.}}
 +
===== Install and configure PulseAudio =====
 +
<pre>
 +
root@cl-som-imx7-sid:~# apt-get install --no-install-recommends pulseaudio pulseaudio-module-bluetooth
 +
</pre>
 +
* Create a systemd service for running pulseaudio as the pulse user.
 +
<pre>
 +
root@cl-som-imx7-sid:~# cat << eof > /etc/systemd/system/pulseaudio.service
 +
[Unit]
 +
Description=Pulse Audio
 +
 +
[Service]
 +
Type=simple
 +
ExecStart=/usr/bin/pulseaudio --system --disallow-exit --disable-shm
 +
 +
[Install]
 +
WantedBy=multi-user.target
 +
eof
 +
 +
root@cl-som-imx7-sid:~# chown pulse:pulse /etc/systemd/system/pulseaudio.service
 +
</pre>
 +
 +
* Create a dbus configuration file for running pulseaudio. Give the pulse user permission to use Bluetooth.
 +
<pre>
 +
root@cl-som-imx7-sid:~# cat << eof > /etc/dbus-1/system.d/pulseaudio-bluetooth.conf
 +
<busconfig>
 +
 +
  <policy user="pulse">
 +
    <allow send_destination="org.bluez"/>
 +
  </policy>
 +
 +
</busconfig>
 +
eof
 +
 +
root@cl-som-imx7-sid:~# chmod 0666 /etc/dbus-1/system.d/pulseaudio-bluetooth.conf
 +
</pre>
 +
* Paste the following lines to the end of /etc/pulse/system.pa:
 +
<pre>
 +
root@cl-som-imx7-sid:~# cat << eof >> /etc/pulse/system.pa
 +
### Automatically load driver modules for Bluetooth hardware
 +
.ifexists module-bluetooth-policy.so
 +
load-module module-bluetooth-policy
 +
.endif
 +
 +
.ifexists module-bluetooth-discover.so
 +
load-module module-bluetooth-discover
 +
.endif
 +
eof
 +
</pre>
 +
* Create {{filename|/var/run/pulse/.config/pulse}} directory. Change its ownership.
 +
<pre>
 +
root@cl-som-imx7-sid:~# mkdir -p /var/run/pulse/.config/pulse
 +
root@cl-som-imx7-sid:~# chown -R pulse:pulse /var/run/pulse
 +
</pre>
 +
* Make the root belong to the pulse-access,audio groups
 +
<pre>
 +
root@cl-som-imx7-sid:~# usermod -a -G pulse-access,audio root
 +
</pre>
 +
 +
===== Start PulseAudio =====
 +
* Start PulseAudio service
 +
<pre>
 +
root@cl-som-imx7-sid:~# systemctl daemon-reload
 +
root@cl-som-imx7-sid:~# systemctl start pulseaudio.service
 +
</pre>
 +
* Make sure that the service is active, running and reports on no errors.
 +
<pre>
 +
root@cl-som-imx7-sid:~# systemctl status pulseaudio.service
 +
  Loaded: loaded (/etc/systemd/system/pulseaudio.service; disabled)
 +
  Active: active (running) since Mon 2015-07-20 12:00:13 UTC; 1min 34s ago
 +
Main PID: 805 (pulseaudio)
 +
  CGroup: /system.slice/pulseaudio.service
 +
          └─805 /usr/bin/pulseaudio --system --disallow-exit --disable-shm
 +
</pre>
 +
 +
===== Bluez5 pairing =====
 +
PulseAudio 5.x supports A2DP per default.<br>
 +
Make sure the following packages are installed:
 +
pulseaudio pulseaudio-module-bluetooth pulseaudio-utils, bluez, bluez-tools.
 +
{{Note|Without {{filename|'''pulseaudio-module-bluetooth'''}} you won't be able to connect after the next pairing and you won't get any usable error messages.}}
 +
 +
* Start the Bluetooth system:
 +
<pre>
 +
root@cl-som-imx7-sid:~# systemctl start bluetooth
 +
</pre>
 +
Now we can use the {{filename|'''bluetoothctl'''}} command line utility to pair and connect. Run
 +
<pre>
 +
root@cl-som-imx7-sid:~# bluetoothctl
 +
[bluetooth]#
 +
</pre>
 +
to be greeted by its internal command prompt.Then enter:
 +
<pre>
 +
[bluetooth]# power on
 +
[bluetooth]# agent on
 +
[bluetooth]# default-agent
 +
[bluetooth]# scan
 +
</pre>
 +
Now make sure that your headset is in pairing mode. It should be discovered shortly. For example,
 +
<pre>
 +
[NEW] Device 00:07:A4:F2:B3:CB Motorola HT820
 +
</pre>
 +
shows a device that calls itself "Motorola HT820" and has MAC address 00:07:A4:F2:B3:CB.
 +
We will now use that MAC address to initiate the pairing:
 +
<pre>
 +
[bluetooth]# pair 00:07:A4:F2:B3:CB
 +
</pre>
 +
After pairing, you also need to explicitly connect the device:
 +
<pre>
 +
[bluetooth]# connect 00:07:A4:F2:B3:CB
 +
</pre>
 +
If everything works correctly, you now have a separate output device in PulseAudio.<br>
 +
You can now disable scanning again and exit the program:
 +
<pre>
 +
[bluetooth]# scan off
 +
[bluetooth]# exit
 +
</pre>
 +
 +
===== Playback using PulseAudio =====
 +
{{Note|Next examples assume that the device mac address is '''00_07_A4_F2_B3_CB'''}}
 +
* Show the PulseAudio device
 +
<pre>
 +
root@cl-som-imx7-sid:~# pactl list cards  | awk '/00_07_A4_F2_B3_CB/' RS=""
 +
Card #1                                                                                                                                                                   
 +
        Name: bluez_card.00_07_A4_F2_B3_CB                                                                                                                                 
 +
        Driver: module-bluez5-device.c                                                                                                                                     
 +
        Owner Module: 13                                                                                                                                                   
 +
        Properties:                                                                                                                                                       
 +
                device.description = "Motorola HT820"                                                                                                                     
 +
                device.string = "00:07:A4:F2:B3:CB"                                                                                                                       
 +
                device.api = "bluez"                                                                                                                                       
 +
                device.class = "sound"                                                                                                                                     
 +
                device.bus = "bluetooth"                                                                                                                                   
 +
                device.form_factor = "headset"                                                                                                                             
 +
                bluez.path = "/org/bluez/hci0/dev_00_07_A4_F2_B3_CB"                                                                                                       
 +
                bluez.class = "0x240404"                                                                                                                                   
 +
                bluez.alias = "Motorola HT820"                                                                                                                             
 +
                device.icon_name = "audio-headset-bluetooth"                                                                                                               
 +
                device.intended_roles = "phone"                                                                                                                           
 +
        Profiles:                                                                                                                                                         
 +
                headset_head_unit: Headset Head Unit (HSP/HFP) (sinks: 1, sources: 1, priority: 20, available: no)
 +
                a2dp_sink: High Fidelity Playback (A2DP Sink) (sinks: 1, sources: 0, priority: 10, available: yes)
 +
                off: Off (sinks: 0, sources: 0, priority: 0, available: yes)
 +
        Active Profile: a2dp_sink
 +
        Ports:
 +
                headset-output: Headset (priority: 0, latency offset: 0 usec)
 +
                        Part of profile(s): headset_head_unit, a2dp_sink
 +
                headset-input: Headset (priority: 0, latency offset: 0 usec, not available)
 +
                        Part of profile(s): headset_head_unit
 +
</pre>
 +
:* Make sure the active card profile is a2dp_sink. Otherwise switch to it:
 +
<pre>
 +
# pactl set-card-profile 1 a2dp_sink
 +
</pre>
 +
:* Show the PulseAudio sink
 +
<pre>
 +
root@cl-som-imx7-sid:~# pactl list sinks | awk '/00_07_A4_F2_B3_CB/' RS=""
 +
Sink #1
 +
        State: SUSPENDED
 +
        Name: bluez_sink.00_07_A4_F2_B3_CB
 +
        Description: Motorola HT820
 +
        Driver: module-bluez5-device.c
 +
        Sample Specification: s16le 2ch 48000Hz
 +
        Channel Map: front-left,front-right
 +
        Owner Module: 13
 +
        Mute: no
 +
        Volume: front-left: 65536 / 100% / 0.00 dB,  front-right: 65536 / 100% / 0.00 dB
 +
                balance 0.00
 +
        Base Volume: 65536 / 100% / 0.00 dB
 +
        Monitor Source: bluez_sink.00_07_A4_F2_B3_CB.monitor
 +
        Latency: 0 usec, configured 0 usec
 +
        Flags: HARDWARE DECIBEL_VOLUME LATENCY
 +
        Properties:
 +
                bluetooth.protocol = "a2dp_sink"
 +
                device.description = "Motorola HT820"
 +
                device.string = "00:07:A4:F2:B3:CB"
 +
                device.api = "bluez"
 +
                device.class = "sound"
 +
                device.bus = "bluetooth"
 +
                device.form_factor = "headset"
 +
                bluez.path = "/org/bluez/hci0/dev_00_07_A4_F2_B3_CB"
 +
                bluez.class = "0x240404"
 +
                bluez.alias = "Motorola HT820"
 +
                device.icon_name = "audio-headset-bluetooth"
 +
                device.intended_roles = "phone"
 +
        Ports:
 +
                headset-output: Headset (priority: 0)
 +
        Active Port: headset-output
 +
        Formats:
 +
                pcm
 +
</pre>
 +
:* Play sound using {{filename|paplay}}. Example:
 +
<pre>
 +
root@cl-som-imx7-sid:~# paplay -d bluez_sink.00_07_A4_F2_B3_CB /path/to/<audio-file.wav>
 +
</pre>
 +
 +
=== Controller–area network (CAN) ===
 +
CL-SOM-iMX7 features two Flexible Controller Area Network (FLEXCAN) modules. Each FLEXCAN implements full CAN protocol version 2.0B and supports both the standard and the extended frame format as well as a programmable data bit rate up to 1Mbit/s.
 +
{{Note|Please prepare the hardware as described in the [[CL-SOM-iMX7: Evaluation Kit: Hardware Guide#CAN | CL-SOM-iMX7  Evaluation Kit Hardware Guide]] and [[SB-SOM: HOWTO: CAN Connection |  CAN node connection guide]].}}
 +
* Software to install {{filename|'''can-utils'''}}
 +
<pre>
 +
root@cl-som-imx7-sid:~# apt-get install --no-install-recommends can-utils
 +
</pre>
 +
 +
===== Loading CAN modules =====
 +
If the FLEXCAN driver and/or Raw CAN protocol compiled as module(s), they must be loaded prior to enabling CAN interface.
 +
 +
* The FLEXCAN driver gets loaded automatically. Make sure it is loaded:
 +
<pre>
 +
root@cl-som-imx7-sid:~# lsmod | grep can
 +
flexcan                10206  0
 +
</pre>
 +
:The FLEXCAN driver can be loaded manually:
 +
<pre>
 +
root@cl-som-imx7-sid:~# modprobe flexcan
 +
30a00000.can supply xceiver not found, using dummy regulator
 +
flexcan 30a00000.can: device registered (reg_base=f5a00000, irq=277)
 +
30a10000.can supply xceiver not found, using dummy regulator
 +
flexcan 30a10000.can: device registered (reg_base=f5a10000, irq=278)
 +
</pre>
 +
* Load Raw CAN protocol module:
 +
<pre>
 +
root@cl-som-imx7-sid:~# modprobe can-raw
 +
can: raw protocol (rev 20120528)
 +
</pre>
 +
 +
===== CAN interface configuration =====
 +
It is recommended configure the CAN interface, with the {{filename|iproute2}} utilities.
 +
 +
* To make sure the right {{filename|ip}} utility is used, run:
 +
<pre>
 +
root@cl-som-imx7-sid:~# ip -V
 +
ip utility, iproute2-ss151103
 +
</pre>
 +
* Configure the CAN interface bit-rate to 125 Kbits/sec (values of up to 1Mbit/sec are supported):
 +
<pre>
 +
root@cl-som-imx7-sid:~# ip link set can0 type can bitrate 125000
 +
</pre>
 +
* Enable the CAN interface:
 +
<pre>
 +
root@cl-som-imx7-sid:~# ip link set can0 up
 +
flexcan 30a00000.can can0: writing ctrl=0x0b312005
 +
</pre>
 +
 +
===== Send/Receive packets =====
 +
Use {{filename|cansend}} and {{filename|candump}} utilities to send and receive packets via CAN interface.
 +
 +
* Send standard CAN frame (on the first device):
 +
<pre>
 +
root@cl-som-imx7-sid:~# cansend can0 111#1122334455667788
 +
</pre>
 +
 +
* Send extended CAN frame (on the first device):
 +
<pre>
 +
root@cl-som-imx7-sid:~# cansend can0 11111111#1122334455667788
 +
</pre>
 +
 +
* Dump all received data frames as well as error frames (on the second device):
 +
<pre>
 +
root@cl-som-imx7-sid:~# candump any,0:0,#FFFFFFFF
 +
  can0  111  [8] 11 22 33 44 55 66 77 88
 +
  can0  11111111  [8] 11 22 33 44 55 66 77 88
 
</pre>
 
</pre>
  
Line 291: Line 700:
 
== See also ==
 
== See also ==
  
 +
* [[CL-SOM-iMX7: Evaluation Kit: Getting Started]]
 +
* [[CL-SOM-iMX7: Evaluation Kit: Hardware Guide]]
 
* [[CL-SOM-iMX7: Linux: Getting started]]
 
* [[CL-SOM-iMX7: Linux: Getting started]]
 
* [[CL-SOM-iMX7: Linux: Kernel]]
 
* [[CL-SOM-iMX7: Linux: Kernel]]

Revision as of 12:12, 29 June 2016

Overview

The example run-time Linux filesystem image for the CompuLab CL-SOM-iMX7 System-on-Module / Computer-on-Module is based on Debian GNU/Linux Sid. The CompuLab Linux package for CL-SOM-iMX7 includes ready to run image, Linux kernel configuration and source code patches, and an archive of the root filesystem, used to create the image.

The default Debian Wheezy Linux image includes more than 400 software packages. Among them:

  • Core system
  • Debian package management system
  • X11 Windowing System
  • Fluxbox desktop manager
  • SSH server and client
  • PulseAudio configuration and usage utilities
  • Bluez5 Bluetooth tools and daemons

The Getting started with Linux on CL-SOM-iMX7 page provides a brief introduction on how to install the run-time Linux image. This article describes package structure and peripheral device options specific to the CL-SOM-iMX7.


Using Debian Linux on CL-SOM-iMX7

Connection and Logging In

Use the following username and password to login:

Account with administrative privileges: 

User: root
Password: 111111

To login into the Linux system, you may use a serial console (ttymxc0) at 115200 bps, or connect through the network (ssh), or use a keyboard and LCD display (tty1,tty2,tty3,tty4).

Networking

To configure networking, edit /etc/network/interfaces, /etc/udev/rules.d/70-persistent-net.rules, /etc/resolv.conf, /etc/hostname and /etc/hosts. For more information about Debian Linux network configuration read:

The majority of network setup can be done via the interfaces configuration file at /etc/network/interfaces.

Admolition note.png auto line is required for interfaces that have to be brought up at boot time.
  • Using DHCP to automatically configure the interface
auto eth0
allow-hotplug eth0
iface eth0 inet dhcp
  • Configuring the interface manually
auto eth0
    iface eth0 inet static
        address 192.168.1.170
        netmask 255.255.0.0
        gateway 192.0.0.1

Consoles

The Linux file system image is designed to suit different kernel versions and configurations. Therefore, during the operating system startup, consoles at several serial ports and LCD display are enabled. Some of these devices may not be supported, either because of kernel versions incompatibilities, or because the kernel was not configured to support these devices. systemd is able to configure most of them. Detail information can be found here:

X Windows system

The CompuLab distribution contains full featured X Windows system with Fluxbox window manager. Before starting X Windows, connect USB mouse and keyboard to the system. You can run X Windows by typing startx.

Software Management

The Debian Linux image for CL-SOM-iMX7 includes all the information required to use Debian package management utilities. You can use apt-get and dpkg out of the box.

Analog Audio

CL-SOM-iMX7 provides an analog audio interface, which is registered as a standard ALSA sound card. Use aplay -l to list all soundcards and digital audio devices registered on the system: 

root@cl-som-imx7-sid:~# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: clsomimx7 [cl-som-imx7], device 0: 308a0000.sai-wm8731-hifi wm8731-hifi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Analog Audio Settings

To enable the Analog audio playback, alsamixer or amixer applications can be used.

  • alsamixer - set the “Output Mixer HiFi” control on.

or

  • amixer - set the “Output Mixer HiFi Playback Switch” control on using command line interface:
root@cl-som-imx7-sid:~# amixer cset numid=14 1
numid=14,iface=MIXER,name='Output Mixer HiFi Playback Switch'
  ; type=BOOLEAN,access=rw------,values=1
  : values=on

Analog Audio Playback

In order to play back a sound file make use of the aplay application.

  • aplay -L can be used for listing of all pcm devices.

Here is a sample output of aplay -L command: 

root@cl-som-imx7-sid:~# aplay -L
null
    Discard all samples (playback) or generate zero samples (capture)
default:CARD=clsomimx7
    cl-som-imx7, 
    Default Audio Device
sysdefault:CARD=clsomimx7
    cl-som-imx7, 
    Default Audio Device
dmix:CARD=clsomimx7,DEV=0
    cl-som-imx7, 
    Direct sample mixing device
dsnoop:CARD=clsomimx7,DEV=0
    cl-som-imx7, 
    Direct sample snooping device
hw:CARD=clsomimx7,DEV=0
    cl-som-imx7, 
    Direct hardware device without any conversions
plughw:CARD=clsomimx7,DEV=0
    cl-som-imx7, 
    Hardware device with all software conversions

The next command can be used for audio play back: 

root@cl-som-imx7-sid:~# aplay <wav-file>

Audio Input Settings

CL-SOM-iMX7 provides an audio capturing feature from either Mic or Line In input sources. alsamixer or amixer can be used in order to switch between these inputs.

Mic
  • alsamixer
Capture Volume => 100
Line Capture Switch => off
Mic Capture Switch => on
Input Mux => Mic
  • amixer
amixer cset numid=3 31
amixer cset numid=4 0
amixer cset numid=6 1
amixer cset numid=11 1
Line In
  • alsamixer
Capture Volume => 100
Line Capture Switch => on
Mic Capture Switch => off
Input Mux => Line In
  • amixer
amixer cset numid=3 31
amixer cset numid=4 1
amixer cset numid=6 0
amixer cset numid=11 0

Sample Audio Recording

As soon as the correct input values have been set, audio signal can be captured. Here is a sample command that shows the arecord usage for capturing audio signal from the selected input line. 

root@cl-som-imx7-sid:~# arecord -f dat -t wav /tmp/out.wav

USB On-The-Go (OTG)

CL-SOM-iMX7 features a high-speed USB 2.0 OTG controller. CL-SOM-iMX7 OTG port is USB host and USB device (gadget) capable.
In CL-SOM-iMX7 default kernel configuration, the USB host driver is compiled into the kernel, whereas USB gadget drivers are compiled as modules.
Gadget drivers should be loaded for OTG support.
Default CL-SOM-iMX7 kernel configuration enables g_serial, g_mass_storage and g_ether gadget drivers. More gadget drivers can be enabled in the kernel configuration.

Testing OTG port

Host mode

Connect USB keyboard to OTG port. 

ci_hdrc ci_hdrc.0: new USB bus registered, assigned bus number 1
ci_hdrc ci_hdrc.0: USB 2.0 started, EHCI 1.00
hub 1-0:1.0: USB hub found
hub 1-0:1.0: 1 port detected
usb 1-1: new low-speed USB device number 2 using ci_hdrc
input: DELL Dell USB Entry Keyboard as /devices/soc.2/30800000.aips-bus/30b10000.usb/ci_hdrc.0/usb1/1-1/1-1:1.0/0003:413C:2107.0002/input/input2
hid-generic 0003:413C:2107.0002: input: USB HID v1.10 Keyboard [DELL Dell USB Entry Keyboard] on usb-ci_hdrc.0-1/input0
Gadget mode
  • g_mass_storage
root@cl-som-imx7-sid:~# modprobe g_mass_storage file=/dev/mmcblk0
	Number of LUNs=8
	Mass Storage Function, version: 2009/09/11
	LUN: removable file: (no medium)
	Number of LUNs=1
	LUN: read only file: /dev/mmcblk0
	Number of LUNs=1
	g_mass_storage gadget: Mass Storage Gadget, version: 2009/09/11
	g_mass_storage gadget: userspace failed to provide iSerialNumber
	g_mass_storage gadget: g_mass_storage ready
	g_mass_storage gadget: high-speed config #1: Linux File-Backed Storage

Connect desktop PC to OTG port.
In case the desktop PC is running Linux, this gadget will show up in the lsusb list: 

Bus 001 Device 047: ID 0525:a4a5 Netchip Technology, Inc. Linux-USB File Storage Gadge

The new device information shows up in the system log. 

[1825168.393211] sd 64:0:0:0: Attached scsi generic sg3 type 0
[1825168.393890] sd 64:0:0:0: [sdd] 15523840 512-byte logical blocks: (7.94 GB/7.40 GiB)
[1825168.499913] sd 64:0:0:0: [sdd] Write Protect is on
[1825168.499919] sd 64:0:0:0: [sdd] Mode Sense: 0f 00 80 00
[1825168.609953] sd 64:0:0:0: [sdd] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
[1825168.839367]  sdd: sdd1
[1825169.059950] sd 64:0:0:0: [sdd] Attached SCSI disk
  • g_ether
root@cl-som-imx7-sid:~# modprobe g_ether
	using random self ethernet address
	using random host ethernet address
	usb0: HOST MAC 12:b1:f6:45:ac:50
	usb0: MAC 7a:89:db:ad:9d:60
	using random self ethernet address
	using random host ethernet address
	g_ether gadget: Ethernet Gadget, version: Memorial Day 2008
	g_ether gadget: g_ether ready
	g_ether gadget: high-speed config #1: CDC Ethernet (ECM)

In case the desktop PC is running Linux, this gadget will show up in the lsusb list: 

Bus 001 Device 009: ID 0525:a4a2 Netchip Technology, Inc. Linux-USB Ethernet/RNDIS Gadget

A new network interface turns out in the ((cmd|ifconfig -a}} list: 

usb0      Link encap:Ethernet  HWaddr 12:b1:f6:45:ac:50  
          inet6 addr: fe80::10b1:f6ff:fe45:ac50/64 Scope:Link
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
  • g_serial
root@cl-som-imx7-sid:~# modprobe g_serial
	g_serial gadget: Gadget Serial v2.4
	g_serial gadget: g_serial ready
	g_serial gadget: high-speed config #2: CDC ACM config

In case the desktop PC is running Linux, this gadget will show up in the lsusb list: 

Bus 001 Device 055: ID 0525:a4a7 Netchip Technology, Inc. Linux-USB Serial Gadget (CDC ACM mode)

The new device information shows up in the system log. 

[184764.380141] cdc_acm 1-1.2.1:2.0: ttyACM0: USB ACM device

WiFi

CL-SOM-iMX7 features 802.11b/g/n wireless connectivity solution, implemented with a TI WiLink8 Combo module.

WiFi Initialization

  • WiFi requires no user interaction for being configured. The driver gets loaded automatically.

Make sure that the WiFi driver is loaded: 

root@cl-som-imx7-sid:~# lsmod | grep wl18xx
wl18xx                 70950  0

The WiFi driver can be loaded manually: 

root@cl-som-imx7-sid:~# modprobe wl18xx
	wlcore: ERROR could not get configuration binary ti-connectivity/wl18xx-conf.bin: -2
	wlcore: WARNING falling back to default config
	wlcore: wl18xx HW: 183x or 180x, PG 2.2 (ROM 0x11)
	wlcore: loaded
  • iwconfig command from wireless-tools package can be used to retrieve detailed information about the WiFi interfaces:
root@cl-som-imx7-sid:~# iwconfig wlan0
wlan0     IEEE 802.11abgn  ESSID:off/any  
          Mode:Managed  Access Point: Not-Associated   Tx-Power=0 dBm   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:on
  • Activate the interface:
root@cl-som-imx7-sid:~# ifconfig wlan0 up
  • Sample WiFi scanning:
root@cl-som-imx7-sid:~# iwlist wlan0 scan

The output will show the list of Access Points and Ad-Hoc cells in range. For more information about connecting to wireless networks and tuning WiFi interfaces refer to “wpa_supplicant” and “wireless-tools” man pages.

wpa_supplicant

  • Configuration sample

wpa_supplicant requires a configuration file to be created in order to get connected to a scanned wireless network.
Make use of the example bellow and put the network name and the password into the "ssid/psk" fields. 

root@cl-som-imx7-sid:~# cat << eof > /etc/wpa_supplicant.conf
ctrl_interface=/var/run/wpa_supplicant

network={
	ssid="wireless_network_name"
	key_mgmt=WPA-PSK
	psk="wireless_network_password"
}
eof
  • Sample run
root@cl-som-imx7-sid:~# ifconfig wlan0 up
root@cl-som-imx7-sid:~# wpa_supplicant -B -Dwext -c /etc/wpa_supplicant.conf -i wlan0
root@cl-som-imx7-sid:~# dhclient wlan0

Bluetooth

CL-SOM-iMX7 features Bluetooth 4.1 BLE interface, implemented with a TI WiLink8 Combo module.

Host Controller Interface (HCI) Initialization

  • HCI requires no user interaction for being configured. The driver gets loaded automatically unless this option has been disabled by putting a black list rule for this device.

Make sure that the Bluetooth driver is loaded: 

root@cl-som-imx7-sid:~# lsmod | grep btwilink
btwilink                3822  0

The Bluetooth driver can be loaded manually: 

root@cl-som-imx7-sid:~# modprobe btwilink
  • HCI device configuration utility can be run to retrieve detailed information about the Bluetooth interfaces:
root@cl-som-imx7-sid:~# hciconfig hci0 -a
hci0:   Type: BR/EDR  Bus: UART
        BD Address: 74:DA:EA:F9:CE:E3  ACL MTU: 1021:6  SCO MTU: 180:4
        UP RUNNING 
        RX bytes:636 acl:0 sco:0 events:39 errors:0
        TX bytes:1234 acl:0 sco:0 commands:39 errors:0
        Features: 0xff 0xfe 0x2d 0xfe 0xdb 0xff 0x7b 0x87
        Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3 
        Link policy: RSWITCH HOLD SNIFF 
        Link mode: SLAVE ACCEPT 
        Name: 'BlueZ 5.36'
        Class: 0x000000
        Service Classes: Unspecified
        Device Class: Miscellaneous, 
        HCI Version: 4.1 (0x7)  Revision: 0x0
        LMP Version: 4.1 (0x7)  Subversion: 0xac03
        Manufacturer: Texas Instruments Inc. (13)
  • If the HCI device is not running, use the below command to enable the HCI device:
root@cl-som-imx7-sid:~# hciconfig hci0 up
  • HCI Inquire remote devices.
root@cl-som-imx7-sid:~# hcitool scan
Scanning ...

Bluez5 & PulseAudio

Debian stretch/sid is using BlueZ 5 and PluseAudio 5, which are fairly new.
BlueZ 5 dropped support for alsa, so the solution for now is to use PulseAudio.
PulseAudio 5 only supports the A2DP profile and not HSP/HFP.

  • Software to install pulseaudio, pulseaudio-module-bluetooth
Admolition note.png debian-image.tar.bz2 has all these packages pre-installed. Continue to the Start PulseAudio section if you use this root filesystem.
Install and configure PulseAudio
root@cl-som-imx7-sid:~# apt-get install --no-install-recommends pulseaudio pulseaudio-module-bluetooth
  • Create a systemd service for running pulseaudio as the pulse user.
root@cl-som-imx7-sid:~# cat << eof > /etc/systemd/system/pulseaudio.service
[Unit]
Description=Pulse Audio

[Service]
Type=simple
ExecStart=/usr/bin/pulseaudio --system --disallow-exit --disable-shm

[Install]
WantedBy=multi-user.target
eof

root@cl-som-imx7-sid:~# chown pulse:pulse /etc/systemd/system/pulseaudio.service
  • Create a dbus configuration file for running pulseaudio. Give the pulse user permission to use Bluetooth.
root@cl-som-imx7-sid:~# cat << eof > /etc/dbus-1/system.d/pulseaudio-bluetooth.conf
<busconfig>

  <policy user="pulse">
    <allow send_destination="org.bluez"/>
  </policy>

</busconfig>
eof

root@cl-som-imx7-sid:~# chmod 0666 /etc/dbus-1/system.d/pulseaudio-bluetooth.conf
  • Paste the following lines to the end of /etc/pulse/system.pa:
root@cl-som-imx7-sid:~# cat << eof >> /etc/pulse/system.pa
### Automatically load driver modules for Bluetooth hardware
.ifexists module-bluetooth-policy.so
load-module module-bluetooth-policy
.endif

.ifexists module-bluetooth-discover.so
load-module module-bluetooth-discover
.endif
eof
  • Create /var/run/pulse/.config/pulse directory. Change its ownership.
root@cl-som-imx7-sid:~# mkdir -p /var/run/pulse/.config/pulse
root@cl-som-imx7-sid:~# chown -R pulse:pulse /var/run/pulse
  • Make the root belong to the pulse-access,audio groups
root@cl-som-imx7-sid:~# usermod -a -G pulse-access,audio root
Start PulseAudio
  • Start PulseAudio service
root@cl-som-imx7-sid:~# systemctl daemon-reload
root@cl-som-imx7-sid:~# systemctl start pulseaudio.service
  • Make sure that the service is active, running and reports on no errors.
root@cl-som-imx7-sid:~# systemctl status pulseaudio.service
   Loaded: loaded (/etc/systemd/system/pulseaudio.service; disabled)
   Active: active (running) since Mon 2015-07-20 12:00:13 UTC; 1min 34s ago
 Main PID: 805 (pulseaudio)
   CGroup: /system.slice/pulseaudio.service
           └─805 /usr/bin/pulseaudio --system --disallow-exit --disable-shm
Bluez5 pairing

PulseAudio 5.x supports A2DP per default.
Make sure the following packages are installed: pulseaudio pulseaudio-module-bluetooth pulseaudio-utils, bluez, bluez-tools.

Admolition note.png Without pulseaudio-module-bluetooth you won't be able to connect after the next pairing and you won't get any usable error messages.
  • Start the Bluetooth system:
root@cl-som-imx7-sid:~# systemctl start bluetooth

Now we can use the bluetoothctl command line utility to pair and connect. Run 

root@cl-som-imx7-sid:~# bluetoothctl
[bluetooth]#

to be greeted by its internal command prompt.Then enter: 

[bluetooth]# power on
[bluetooth]# agent on
[bluetooth]# default-agent
[bluetooth]# scan

Now make sure that your headset is in pairing mode. It should be discovered shortly. For example, 

[NEW] Device 00:07:A4:F2:B3:CB Motorola HT820

shows a device that calls itself "Motorola HT820" and has MAC address 00:07:A4:F2:B3:CB. We will now use that MAC address to initiate the pairing: 

[bluetooth]# pair 00:07:A4:F2:B3:CB

After pairing, you also need to explicitly connect the device: 

[bluetooth]# connect 00:07:A4:F2:B3:CB

If everything works correctly, you now have a separate output device in PulseAudio.
You can now disable scanning again and exit the program: 

[bluetooth]# scan off
[bluetooth]# exit
Playback using PulseAudio
Admolition note.png Next examples assume that the device mac address is 00_07_A4_F2_B3_CB
  • Show the PulseAudio device
root@cl-som-imx7-sid:~# pactl list cards  | awk '/00_07_A4_F2_B3_CB/' RS=""
Card #1                                                                                                                                                                     
        Name: bluez_card.00_07_A4_F2_B3_CB                                                                                                                                  
        Driver: module-bluez5-device.c                                                                                                                                      
        Owner Module: 13                                                                                                                                                    
        Properties:                                                                                                                                                         
                device.description = "Motorola HT820"                                                                                                                       
                device.string = "00:07:A4:F2:B3:CB"                                                                                                                         
                device.api = "bluez"                                                                                                                                        
                device.class = "sound"                                                                                                                                      
                device.bus = "bluetooth"                                                                                                                                    
                device.form_factor = "headset"                                                                                                                              
                bluez.path = "/org/bluez/hci0/dev_00_07_A4_F2_B3_CB"                                                                                                        
                bluez.class = "0x240404"                                                                                                                                    
                bluez.alias = "Motorola HT820"                                                                                                                              
                device.icon_name = "audio-headset-bluetooth"                                                                                                                
                device.intended_roles = "phone"                                                                                                                             
        Profiles:                                                                                                                                                           
                headset_head_unit: Headset Head Unit (HSP/HFP) (sinks: 1, sources: 1, priority: 20, available: no)
                a2dp_sink: High Fidelity Playback (A2DP Sink) (sinks: 1, sources: 0, priority: 10, available: yes)
                off: Off (sinks: 0, sources: 0, priority: 0, available: yes)
        Active Profile: a2dp_sink
        Ports:
                headset-output: Headset (priority: 0, latency offset: 0 usec)
                        Part of profile(s): headset_head_unit, a2dp_sink
                headset-input: Headset (priority: 0, latency offset: 0 usec, not available)
                        Part of profile(s): headset_head_unit
  • Make sure the active card profile is a2dp_sink. Otherwise switch to it:
# pactl set-card-profile 1 a2dp_sink
  • Show the PulseAudio sink
root@cl-som-imx7-sid:~# pactl list sinks | awk '/00_07_A4_F2_B3_CB/' RS=""
Sink #1
        State: SUSPENDED
        Name: bluez_sink.00_07_A4_F2_B3_CB
        Description: Motorola HT820
        Driver: module-bluez5-device.c
        Sample Specification: s16le 2ch 48000Hz
        Channel Map: front-left,front-right
        Owner Module: 13
        Mute: no
        Volume: front-left: 65536 / 100% / 0.00 dB,   front-right: 65536 / 100% / 0.00 dB
                balance 0.00
        Base Volume: 65536 / 100% / 0.00 dB
        Monitor Source: bluez_sink.00_07_A4_F2_B3_CB.monitor
        Latency: 0 usec, configured 0 usec
        Flags: HARDWARE DECIBEL_VOLUME LATENCY 
        Properties:
                bluetooth.protocol = "a2dp_sink"
                device.description = "Motorola HT820"
                device.string = "00:07:A4:F2:B3:CB"
                device.api = "bluez"
                device.class = "sound"
                device.bus = "bluetooth"
                device.form_factor = "headset"
                bluez.path = "/org/bluez/hci0/dev_00_07_A4_F2_B3_CB"
                bluez.class = "0x240404"
                bluez.alias = "Motorola HT820"
                device.icon_name = "audio-headset-bluetooth"
                device.intended_roles = "phone"
        Ports:
                headset-output: Headset (priority: 0)
        Active Port: headset-output
        Formats:
                pcm
  • Play sound using paplay. Example:
root@cl-som-imx7-sid:~# paplay -d bluez_sink.00_07_A4_F2_B3_CB /path/to/<audio-file.wav>

Controller–area network (CAN)

CL-SOM-iMX7 features two Flexible Controller Area Network (FLEXCAN) modules. Each FLEXCAN implements full CAN protocol version 2.0B and supports both the standard and the extended frame format as well as a programmable data bit rate up to 1Mbit/s.

Admolition note.png Please prepare the hardware as described in the CL-SOM-iMX7 Evaluation Kit Hardware Guide and CAN node connection guide.
  • Software to install can-utils
root@cl-som-imx7-sid:~# apt-get install --no-install-recommends can-utils
Loading CAN modules

If the FLEXCAN driver and/or Raw CAN protocol compiled as module(s), they must be loaded prior to enabling CAN interface.

  • The FLEXCAN driver gets loaded automatically. Make sure it is loaded:
root@cl-som-imx7-sid:~# lsmod | grep can
flexcan                10206  0
The FLEXCAN driver can be loaded manually:
root@cl-som-imx7-sid:~# modprobe flexcan
30a00000.can supply xceiver not found, using dummy regulator
flexcan 30a00000.can: device registered (reg_base=f5a00000, irq=277)
30a10000.can supply xceiver not found, using dummy regulator
flexcan 30a10000.can: device registered (reg_base=f5a10000, irq=278)
  • Load Raw CAN protocol module:
root@cl-som-imx7-sid:~# modprobe can-raw
can: raw protocol (rev 20120528)
CAN interface configuration

It is recommended configure the CAN interface, with the iproute2 utilities.

  • To make sure the right ip utility is used, run:
root@cl-som-imx7-sid:~# ip -V
ip utility, iproute2-ss151103
  • Configure the CAN interface bit-rate to 125 Kbits/sec (values of up to 1Mbit/sec are supported):
root@cl-som-imx7-sid:~# ip link set can0 type can bitrate 125000
  • Enable the CAN interface:
root@cl-som-imx7-sid:~# ip link set can0 up
flexcan 30a00000.can can0: writing ctrl=0x0b312005
Send/Receive packets

Use cansend and candump utilities to send and receive packets via CAN interface.

  • Send standard CAN frame (on the first device):
root@cl-som-imx7-sid:~# cansend can0 111#1122334455667788
  • Send extended CAN frame (on the first device):
root@cl-som-imx7-sid:~# cansend can0 11111111#1122334455667788
  • Dump all received data frames as well as error frames (on the second device):
root@cl-som-imx7-sid:~# candump any,0:0,#FFFFFFFF
  can0  111  [8] 11 22 33 44 55 66 77 88
  can0  11111111  [8] 11 22 33 44 55 66 77 88

Touchscreen

See Touchscreen controllers support sections for kernel configuration details to enable support for the particular touchscreen. The touchscreen driver is modularized if you use default CL-SOM-iMX7 configuration and is not loaded by udev automatically on Linux boot. Use the following command to load the touchscreen driver module:

  • For TI TSC2046 touch panel:
root@cl-som-imx7-sid:~# modprobe ads7846

The X Windows system of CL-SOM-iMX7 uses tslib X server input driver to get the input from the touchscreen.

Touchscreen calibration

All supported touchscreen devices can be calibrated using xinput_calibrator utility.

To calibrate the touchscreen:

  • Run X Server by issuing '''startx &''' command
  • Make sure the touchscreen driver is loaded as described in Touchscreen section
  • Set the DISPLAY environment variable:
 export DISPLAY=:0
  • Run '''xinput_calibrator''' utility. For proper calibration you are required to touch the touchscreen corners and center in the following order: top-left, top-right, bottom-right, bottom-left, center.
  • Create a file /usr/share/X11/xorg.conf.d/99-calibration.conf and paste there a snippet with the calibration results:
root@cl-som-imx7-sid:~# xinput_calibrator 
Setting calibration data: 0, 4095, 0, 4095
Calibrating EVDEV driver for "ADS7846 Touchscreen" id=6
        current calibration values (from XInput): min_x=0, max_x=4095 and min_y=0, max_y=4095

Doing dynamic recalibration:
        Setting calibration data: 165, 3864, 3789, 268
        --> Making the calibration permanent <--
  copy the snippet below into '/etc/X11/xorg.conf.d/99-calibration.conf' (/usr/share/X11/xorg.conf.d/ in some distro's)
Section "InputClass"
        Identifier      "calibration"
        MatchProduct    "ADS7846 Touchscreen"
        Option  "Calibration"   "165 3864 3789 268"
        Option  "SwapAxes"      "0"
EndSection

MMC/SD

The support for MMC/SD card on CL-SOM-iMX7 is built into the Linux kernel. To mount a memory card, monitor /proc/partitions to see what partitions were detected on the MMC/SD card. For example, suppose an MMC/SD partition you'd like to mount is mmcblk0p1 then: 

if [ ! -d /mnt/mmcblk0p1 ]; then mkdir /mnt/mmcblk0p1; fi
mount /dev/mmcblk0p1 /mnt/mmcblk0p1

GPIO access

Linux provides simple and convenient GPIO access via sysfs interface. A GPIO should be exported using /sys/class/gpio/export. After the GPIO is exported it is possible to change its direction and value using /sys/class/gpio/gpioX/direction and /sys/class/gpio/gpioX/value attributes.

Example

The following example demonstrates how to configure GPIO 140 as output and set value to high: 

root@cl-som-imx7-sid:~# echo 140 > /sys/class/gpio/export
root@cl-som-imx7-sid:~# echo out > /sys/class/gpio/gpio140/direction
root@cl-som-imx7-sid:~# echo 1 > /sys/class/gpio/gpio140/value
Admolition note.png The above example assumes that the corresponding pin is set to mux mode 5 and the GPIO 140 is not requested in the Linux kernel.

See also

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