CL-SOM-iMX7: Linux: Debian

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 Automatic Linux installation 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

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.

Networking

To configure networking, edit /etc/network/interfaces, /etc/resolv.conf, /etc/hostname and /etc/hosts. For more information about Debian Linux network configuration read:

• Network setup chapter in the Debian Reference
• Network chapter in the Debian Wiki

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

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:

• Systemd getty generator [systemd-getty-generator]
• Gettys on Serial Consoles [serial-console]

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

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
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-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.

Mic

• 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)

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-rootfs:~# lsmod | grep wl18xx
wl18xx                 70950  0

The WiFi driver can be loaded manually:

root@cl-rootfs:~# 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-rootfs:~# 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-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.

wpa_supplicant

• Configuration sample

Please open a wpa_supplicant configuration file bellow and put a network name and a password into the "ssid" and "psk" fields respectively.

root@cl-rootfs:~# cat /etc/wpa_supplicant.conf
ctrl_interface=/var/run/wpa_supplicant

network={
	ssid="wireless_network_name"
	key_mgmt=WPA-PSK
	psk="wireless_network_password"
}

• 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

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-debian:~# lsmod | grep hci_uart
hci_uart               10445  1

The Bluetooth driver can be loaded manually:

root@cl-rootfs:~# modprobe hci_uart

• HCI device configuration utility can be run to retrieve detailed information about the Bluetooth interfaces:

root@cl-rootfs:~# hciconfig hci0 -a
hci0:   Type: Primary  Bus: UART
        BD Address: 3C:A3:08:A8:03:B9  ACL MTU: 1021:6  SCO MTU: 180:4
        UP RUNNING 
        RX bytes:746 acl:0 sco:0 events:49 errors:0
        TX bytes:3441 acl:0 sco:0 commands:49 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: 'cl-debian'
        Class: 0x0c0000
        Service Classes: Rendering, Capturing
        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-rootfs:~# hciconfig hci0 up

• HCI Inquire remote devices.

root@cl-rootfs:~# hcitool scan
Scanning ...

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.

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 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.

Example

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

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

• CL-SOM-iMX7: Evaluation Kit: Getting Started
• CL-SOM-iMX7: Evaluation Kit: Hardware Guide
• CL-SOM-iMX7: Linux: Automatic Installation
• CL-SOM-iMX7: Linux: Manual Installation
• CL-SOM-iMX7: Linux: Kernel
• Linux: Development for ARM modules
• Linux: Debian: Minimal ARM filesystem
• Debian Reference.