UCM-iMX7: Linux: Debian

From Compulab Mediawiki
Jump to: navigation, search


The example run-time Linux filesystem image for the CompuLab UCM-iMX7 System-on-Module / Computer-on-Module is based on Debian GNU/Linux Sid. The CompuLab Linux package for UCM-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 Automatic Linux installation on UCM-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 UCM-iMX7.

Admolition note.png The article uses cl-rootfs hostname. A real hostname may be different.

Using Debian Linux on UCM-iMX7

Connection and Logging In

This Debian rootfs comes with a default sudo user compulab:

Debian GNU/Linux 10 cl-debian ttymxc0

cl-debian login: compulab
Password: compulab

This Debian rootfs comes without default root password. The root password has to be set at the very first login:

Debian GNU/Linux 10 cl-debian ttymxc0

cl-debian login: root
You are required to change your password immediately (administrator enforced)
New password: 
Retype new password: 

To login into the Linux system, you may use a serial console, or connect through the network (ssh), or use a keyboard and display.


To configure networking, edit /etc/network/interfaces, /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


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 and derived products includes all the information required to use Debian package management utilities. You can use apt-get and dpkg out of the box.

Analog Audio

UCM-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-rootfs:~# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: ucmimx7 [ucm-imx7], device 0: 308a0000.sai-wm8731-hifi wm8731-hifi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Use aplay -l to list all sound cards and digital audio devices registered on the system:

root@cl-rootfs:~# 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 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-rootfs:~# aplay -L
    Discard all samples (playback) or generate zero samples (capture)
    Default Audio Device
    Default Audio Device
    Direct sample mixing device
    Direct sample snooping device
    Direct hardware device without any conversions
    Hardware device with all software conversions

The next command can be used for audio play back:

root@cl-rootfs:~# aplay -D sysdefault <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.

  • alsamixer
Capture Volume => 100
Line Capture Switch => off
Mic Capture Switch => on
Input Mux => Mic
  • amixer
amixer cset numid=1 65536
amixer -c 0 cset numid=3 31,31
amixer -c 0 cset numid=4 0
amixer -c 0 cset numid=6 1
amixer -c 0 cset numid=14 1
Line In
  • alsamixer
Capture Volume => 100
Line Capture Switch => on
Mic Capture Switch => off
Input Mux => Line In
  • amixer
amixer cset numid=1 65536
amixer -c 0 cset numid=3 31
amixer -c 0 cset numid=4 1
amixer -c 0 cset numid=6 0
amixer -c 0 cset numid=14 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-rootfs:~# arecord -D sysdefault -d 10 -f dat -t wav /tmp/out.wav

USB On-The-Go (OTG)

This section describes USB OTG port (USB host and USB device (gadget) capable port) use cases for following Compulab devices built around the NXP i.MX7 SoC:

  • CL-SOM-iMX7
  • UCM-iMX7

In the 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 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-rootfs:~# 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-rootfs:~# 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-rootfs:~# 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


UCM-iMX7 features 802.11b/g/n wireless connectivity solution, implemented with a Broadcom BCM4343W chipset.

WiFi Initialization

  • WiFi requires no user interaction for being configured. The driver gets loaded automatically by the means of /etc/modules-load.d/wifi.conf configuration file. The driver options are specified with the options file /etc/modprobe.d/bcmdhd.conf. Make sure that the WiFi driver is loaded:
root@cl-rootfs:~# lsmod | grep bcmdhd
bcmdhd                597255  0
  • The WiFi driver can be loaded manually.
  • Create the driver options file:
cat << eof > /etc/modprobe.d/bcmdhd.conf
options bcmdhd firmware_path=/lib/firmware/brcm/1DX/fw_bcmdhd.bin
options bcmdhd nvram_path=/lib/firmware/brcm/1DX/bcmdhd.1DX.SDIO.cal
options bcmdhd dhd_msg_level=0x1
  • Load the WiFi driver module:
root@cl-debian:~# modprobe bcmdhd 
dhd_module_init in
Register interface [wlan0]  MAC: b0:72:bf:09:b5:fc
  • iwconfig command from wireless-tools package can be used to retrieve detailed information about the WiFi interfaces:
root@cl-rootfs:~# iwconfig wlan0
wlan0     IEEE 802.11bg  ESSID:off/any  
          Mode:Managed  Access Point: Not-Associated   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:on
  • Activate the interface:
root@cl-rootfs:~# ifconfig wlan0 up
  • Sample WiFi scanning:
root@cl-rootfs:~# 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.


  • 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-rootfs:~# cat << eof > /etc/wpa_supplicant.conf

  • Sample run
root@cl-rootfs:~# ifconfig wlan0 up
root@cl-rootfs:~# wpa_supplicant -B -Dwext -c /etc/wpa_supplicant.conf -i wlan0
root@cl-rootfs:~# dhclient wlan0


UCM-iMX7 features Bluetooth 4.1 + High Speed (HS) interface. Following sections describe the initialization and simple use cases of the Bluetooth interface.

Host Controller Interface (HCI) Initialization

  • Start Bluetooth:
root@cl-debian:~# bt-start 
Set Controller UART speed to 3000000 bit/s
Flash firmware /etc/firmware/BCM43430A1.1DX.hcd
Set Controller UART speed to 3000000 bit/s
Bluetooth: HCI UART driver ver 2.3
Bluetooth: HCI UART protocol H4 registered
Bluetooth: HCI UART protocol BCM registered
Device setup complete
  • Make sure that the Bluetooth drivers are loaded:
root@cl-debian:~# lsmod
Module                  Size  Used by
hci_uart                7594  1
btbcm                   5344  1 hci_uart
  • HCI device configuration utility can be run to retrieve detailed information about the Bluetooth interfaces:
root@cl-debian:~# hciconfig -a
hci0:   Type: BR/EDR  Bus: UART
        BD Address: 43:43:A1:12:1F:AC  ACL MTU: 1021:8  SCO MTU: 64:1
        UP RUNNING 
        RX bytes:675 acl:0 sco:0 events:39 errors:0
        TX bytes:1271 acl:0 sco:0 commands:39 errors:0
        Features: 0xbf 0xfe 0xcf 0xfe 0xdb 0xff 0x7b 0x87
        Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3 
        Link policy: RSWITCH SNIFF 
        Link mode: SLAVE ACCEPT 
        Name: 'BlueZ 5.36'
        Class: 0x000000
        Service Classes: Unspecified
        Device Class: Miscellaneous, 
        HCI Version: 4.0 (0x6)  Revision: 0x16
        LMP Version: 4.0 (0x6)  Subversion: 0x2209
        Manufacturer: Broadcom Corporation (15)
  • If the HCI device is not running, use the below command to enable the HCI device:
root@cl-debian:~# hciconfig hci0 up

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-rootfs:~# apt-get install --no-install-recommends pulseaudio pulseaudio-module-bluetooth
  • Create a systemd service for running pulseaudio as the pulse user.
root@cl-rootfs:~# cat << eof > /etc/systemd/system/pulseaudio.service
Description=Pulse Audio

ExecStart=/usr/bin/pulseaudio --system --disallow-exit --disable-shm


root@cl-rootfs:~# 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-rootfs:~# cat << eof > /etc/dbus-1/system.d/pulseaudio-bluetooth.conf

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


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

.ifexists module-bluetooth-discover.so
load-module module-bluetooth-discover
  • Create /var/run/pulse/.config/pulse directory. Change its ownership.
root@cl-rootfs:~# mkdir -p /var/run/pulse/.config/pulse
root@cl-rootfs:~# chown -R pulse:pulse /var/run/pulse
  • Make the root belong to the pulse-access,audio groups
root@cl-rootfs:~# usermod -a -G pulse-access,audio root
Start PulseAudio
  • Start PulseAudio service
root@cl-rootfs:~# systemctl daemon-reload
root@cl-rootfs:~# systemctl start pulseaudio.service
  • Make sure that the service is active, running and reports on no errors.
root@cl-rootfs:~# 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-rootfs:~# systemctl start bluetooth

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

root@cl-rootfs:~# bluetoothctl

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

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

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-rootfs:~# 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                                                                                                                                                    
                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"                                                                                                                             
                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
                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-rootfs:~# pactl list sinks | awk '/00_07_A4_F2_B3_CB/' RS=""
Sink #2
        State: SUSPENDED
        Name: bluez_sink.00_07_A4_F2_B3_CB.a2dp_sink
        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.a2dp_sink.monitor
        Latency: 0 usec, configured 0 usec
                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"
                headset-output: Headset (priority: 0)
        Active Port: headset-output
  • Play sound using paplay. Example:
root@cl-rootfs:~# paplay -d bluez_sink.00_07_A4_F2_B3_CB.a2dp_sink /path/to/<audio-file.wav>

Controller–area network (CAN)

UCM-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 UCM-iMX7 Evaluation Kit Hardware Guide and CAN node connection guide.
Software installation
  • Use the following command to install can-utils:
root@cl-rootfs:~# 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-rootfs:~# lsmod | grep can
flexcan                102  0
The FLEXCAN driver can be loaded manually:
root@cl-rootfs:~# 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-rootfs:~# 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-rootfs:~# 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-rootfs:~# ip link set can0 type can bitrate 125000
  • Enable the CAN interface:
root@cl-rootfs:~# 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-rootfs:~# cansend can0 111#1122334455667788
  • Send extended CAN frame (on the first device):
root@cl-rootfs:~# cansend can0 11111111#1122334455667788
  • Dump all received data frames as well as error frames (on the second device):
root@cl-rootfs:~# 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


The touchscreen driver is modularized if you use default UCM-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-rootfs:~# modprobe ads7846

The X Windows system of UCM-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-rootfs:~# 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"


The support for MMC/SD card on Compulab devices based on the NXP iMX7 SoC 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.


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

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

See also