UCM-iMX91: Yocto Linux: How-To Guide

Device Tree

Available Device Tree Files

The current release includes the following dtb files:

DTB	Hardware Configuration and Features	Jumpers/Connectors Settings
ucm-imx91.dtb	default hardware configuration

Set device tree

The current release provides two methods to switch between dtb files:

• U-Boot environment

The U-boot fdtfile variable contains the device tree name that will be loaded into the RAM. This variable can be changed by:

Environment	Command
U-Boot	setenv fdtfile <fdt_file_name>; saveenv;
Linux	fw_setenv fdtfile <fdt_file_name>

• GRUB environment (if the image was created with the meta-compulab-uefi layer)

Environment	Command/Procedure
GRUB Boot Menu	Goto "Advanced Boot Options" and choose a device tree from the provided dtb list.
Linux	grub-editenv /boot/grub/grubenv set fdtfile=<fdt_file_name>

Serial Console

UCM-iMX91 provides serial console on UART1.
SB-UCMIMX91 evaluation carrier-board exposes the console UART via CP2104 serial-to-USB bridge on connector P16.

Connecting to a host PC

1. Use a micro-USB cable to connect the console connector P16 to a USB port on your host PC.
2. Make sure the CP2104 driver is available with your operating system, otherwise install CP2104 driver onto the host PC from https://www.silabs.com/documents/public/software/CP210x_Windows_Drivers_with_Serial_Enumeration.zip
3. Identify the host PC interface and port number that will be used for communication with the UCM-iMX91 evaluation kit:
   • In most Linux PCs, the serial port will be denoted as one of the following (where n is a positive integer): /dev/ttyUSB0, /dev/ttyUSB1 ... /dev/ttyUSBn
   • In Windows PCs, the serial port usually will be denoted as one of the following (where n is a positive integer): COM1, COM2 ... COMn
4. Start a terminal emulation program (such as PuTTY on Windows or minicom on Linux).
5. In the port configuration section of the terminal emulation program select the port identified in previous step and set the following serial port parameters:

Baud Rate	Data Bits	Stop Bits	Parity	Flow Control
115200	8	1	none	none

USB

UCM-IMX91 features two USB2.0 ports that are derived from the i.MX91 USB sub-system.
On SB-UCMIMX91 evaluation carrier-board USB ports are available on the following connectors:

USB port#	HW setting	Connector	Mode
1	P21 is not used	type-A J5	host
1	P21 connected to USB host	micro-USB P21	device
2	jumper E11 is open	type-A J6	host
2	jumper E11 is closed	mini-PCIe P18	host

USB #1 in device mode

USB #1 port can be operated in device mode when connected to a host machine using connector P21.
Available gadgets for the UBS #1 in device mode:

USB gadget	SOM command
usb serial device	modprobe g_serial
usb network device	modprobe g_ether
usb mass storage device	modprobe g_mass_storage file=/dev/sdX

CAN bus

UCM-iMX91 features two Flexible Controller Area Network (FLEXCAN) modules. SB-UCMIMX91 evaluation carrier-board exposes one CAN bus interface on connector J21.

• Configure both CAN interface bit-rate to 1 Mbit/sec:

ip link set can0 up type can bitrate 1000000

• On one system, dump all received data frames as well as error frames:

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
...
  can0  03FF0983   [8]  D7 61 FF 03 C1 F7 C1 34
  can0  19C34D32   [8]  F7 5A C2 73 AD 0E 3F 0B
  can0  0675E391   [4]  2B 2D D3 49
  can0  13091C55   [8]  99 32 EC 77 27 81 49 0B
  can0  098D67CF   [8]  22 50 AB 48 AD 7F F4 26
  can0  05263FEC   [5]  1B 4C 02 45 6E
  can0  12B30E20   [0] 
  can0  1F191DF9   [1]  C5
  can0  1EB0B18F   [8]  3E 3F DA 57 C2 FE 73 58
  can0  1E5C64D9   [5]  6F 0D B3 63 6A
  can0  1E1DE3F9   [8]  96 48 AC 79 4E 00 27 71
  can0  0E1A11B7   [8]  75 81 70 7C 86 79 A7 77
  can0  05F8FD8B   [7]  33 F9 9B 1E 77 3D 1F
  can0  1E155FCD   [8]  E6 BA F8 58 ED 6D C8 10
  can0  1D91DF9E   [8]  5D 29 82 7B 97 1D AB 5C
  can0  11FB3CDA   [3]  14 65 C3
  can0  091352C0   [2]  2C ED
...

On second system:

• Send standard CAN frame:

cansend can0 111#1122334455667788

• Send extended CAN frame:

cansend can0 11111111#1122334455667788

• CAN frames (extended mode) generator, random payload, interval between two successive flames 50 msec:

cangen -g 50 -e -D r -v can0

can: raw protocol (rev 20170425)
...
  can0  03FF0983#D7.61.FF.03.C1.F7.C1.34
  can0  19C34D32#F7.5A.C2.73.AD.0E.3F.0B
  can0  0675E391#2B.2D.D3.49
  can0  13091C55#99.32.EC.77.27.81.49.0B
  can0  098D67CF#22.50.AB.48.AD.7F.F4.26
  can0  05263FEC#1B.4C.02.45.6E
  can0  12B30E20#
  can0  1F191DF9#C5
  can0  1EB0B18F#3E.3F.DA.57.C2.FE.73.58
  can0  1E5C64D9#6F.0D.B3.63.6A
  can0  1E1DE3F9#96.48.AC.79.4E.00.27.71
  can0  0E1A11B7#75.81.70.7C.86.79.A7.77
  can0  05F8FD8B#33.F9.9B.1E.77.3D.1F
  can0  1E155FCD#E6.BA.F8.58.ED.6D.C8.10
  can0  1D91DF9E#5D.29.82.7B.97.1D.AB.5C
  can0  11FB3CDA#14.65.C3
  can0  091352C0#2C.ED
...

Bluetooth

UCM-iMX91 features Bluetooth connectivity implemented with an NXP 88W8997 module.

Before working with Bluetooth, please ensure that Bluetooth antenna is connected to the SOM.

To start bluetoothctl use the following command:

bluetoothctl

To start the scan process use the following commands:

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

Bluetooth device should be turned on and visible. Its MAC-adress and name should appear in bluetoothctl in following format:

[CHG] Device AA:BB:CC:DD:EE:FF Name: Device_Name

To pair with the Bluetooth device use the following command:

pair AA:BB:CC:DD:EE:FF

Where AA:BB:CC:DD:EE:FF is MAC-adress of the Bluetooth device.

To quit bluetoothctl use the following command:

[Device_Name]# quit

Cellular Modem

UCM-IMX91 Yocto includes support for Quectel EC25 mini-PCIe cellular modem that can be installed into the evaluation kit.

• Install the modem module into the mini-PCIe socket P18
• Close jumper E11
• Connect a cellular antenna to the main antenna connector on the modem
• Install an active SIM card into SIM socket P20
• Boot to linux

Run the following command to verify that the modem is detected correctly:

root@ucm-imx91:~# lsusb                                                                                                                                                                                            
Bus 001 Device 002: ID 2c7c:0125 Quectel Wireless Solutions Co., Ltd. EC25 LTE modem                                                                                                                               

root@ucm-imx91:~# mmcli -L                                                                                                                                                                                         
    /org/freedesktop/ModemManager1/Modem/0 [QUALCOMM INCORPORATED] QUECTEL Mobile Broadband Module                                                                                                                 

Obtain <apn> of your sim card company ,e.g. rl.internet

Establish connection:

root@ucm-imx91:~# nmcli connection add type gsm ifname '*' con-name CellularCon apn <apn>
root@ucm-imx91:~# nmcli connection
NAME                UUID                                  TYPE      DEVICE   
CellularCon         a1620622-8588-4349-b3fc-66be79fbbede  gsm       cdc-wdm0 

Allow up to a minute to connect to wireless network and make sure modem state is connected:

root@ucm-imx91:~#mmcli -m 0

To test the wireless interface run:

root@ucm-imx91:~#ping -c 5 dns.google -I wwan0

UART

The following table outlines default UART routing when UCM-iMX91 is used with the SB-UCMIMX91 carrier-board:

UCM-iMX91 port	Linux device	on SB-UCMIMX91 carrier-board
UART1	/dev/ttyLP0	converted to serial-over-USB debug console, micro-USB connector P16
UART2	/dev/ttyLP1	converted to RS232, DB9 connector P17
UART5	/dev/ttyLP4	routed to 100-mil header P3
UART7	/dev/ttyLP6	converted to RS485, terminal block J22

Example: testing UART5

• Short pin P3-1 (UART5-RX) with P3-3 (UART5-TX) on SB-UCMIMX91 to create a loop-back.
• Run the following commands:

stty -F /dev/ttyLP4 1:0:1cb2:0:3:1c:7f:15:4:5:1:0:11:13:1a:0:12:f:17:16:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0
cat /dev/ttyLP4 &
echo hello > /dev/ttyLP4

The "hello" string should appear on the terminal.

I2C

The following I2C buses and devices are present when UCM-iMX91 is used with the SB-UCMIMX91 carrier-board:

Device	I2C bus in Linux	Address	HW port in UCM-iMX91
UCM-iMX91 EEPROM	0	0x50	I2C1 (internal)
UCM-iMX91 RTC	0	0x69	I2C1 (internal)
UCM-iMX91 PMIC	1	0x25	I2C2 (internal)
GPIO extender on SB-UCMIMX91 for on-board control signals	2	0x20	I2C3
Camera module control on SB-UCMIMX91 connector P9	2	0x42	I2C3
SB-UCMIMX91 EEPROM	2	0x54	I2C3
Touch-screen controller of MIPI-DSI or LVDS panel on SB-UCMIMX91 connector P8 or P12	2	0x5d	I2C3

To list all mapped devices:

# ls /proc/device-tree/soc@0/bus@*/i2c@*/*@* -d -w 1                                                                                                         
/proc/device-tree/soc@0/bus@42000000/i2c@42530000/goodix@5d
/proc/device-tree/soc@0/bus@42000000/i2c@42530000/mipi2@42
/proc/device-tree/soc@0/bus@42000000/i2c@42530000/pca9555@20
/proc/device-tree/soc@0/bus@44000000/i2c@44340000/rtc@69
/proc/device-tree/soc@0/bus@44000000/i2c@44350000/pmic@25

Note how:

• each node is appended with its address.
• I2C buses order corresponds to the order of their addresses.

e.g. to inspect bus 0, in which we have RTC, run:

# i2cdetect -y 0
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: 50 51 52 53 -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- UU -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         

In the above output numbers mark unused devices, UU marks a device that is used by a driver.

Indeed we see RTC in use at offset 0x69.

An example how to dump EEPROM contents:

hexdump -C /sys/devices/platform/soc@0/44000000.bus/44340000.i2c/i2c-0/0-0050/eeprom

SPI

Loopback example:

In order to enable SPI device, it needs to be added to the device tree in the following manner:

Set up the kernel source repository by following the instructions in this guide: https://github.com/compulab-yokneam/meta-bsp-imx9/blob/mickledore-6.1.55-2.0/Documentation/linux_kernel_build.md

However, stop before the final command that builds the kernel.

Instead of building the full kernel, run:

make dtbs

Locate the compiled device tree:

arch/arm64/boot/dts/compulab/ucm-imx91-lpspi.dtb

On the UCM-IMX91, identify your boot partition by running:

lsblk

Then, copy the .dtb file to that partition.

Restart your device and interrupt the boot process to access U-Boot. Then run:

setenv fdtfile ucm-imx91-lpspi.dtb; boot

SPI signals location:

ECSPI3_MOSI - P3.14
ECSPI3_SCLK - P3.16
ECSPI3_MISO/UART7_RX - U25 pin 1 (beside RS485)
ECSPI3_SSO/UART7_TX - U25 pin 4 (beside RS485)

Use jumper cable to connect MOSI and MISO.

On the module, run:

spidev_test -v -D /dev/spidev0.0 -p "hello"

You should see RX same as TX.

GPIO

The following table outlines default GPIO assignments when UCM-iMX91 is used with the SB-UCMIMX91 carrier-board:

Signal Name	Pin on SB-UCMIMX91
GPIO_IO04	P3-20
GPIO_IO05	P3-18
GPIO_IO07	P3-6
GPIO_IO14	P5-4
GPIO_IO15	P5-2
GPIO_IO16	P3-4

Other signals that are reserved for peripheral controls can be reassigned to GPIOs in

arch/arm64/boot/dts/compulab/ucm-imx91-pinctrl.dtsi

Example: controlling pin GPIO_IO16

Checking the pin info

gpioinfo -c 0

This lists all GPIO lines in `gpiochip0`, including GPIO_IO16 (line offset 16).

Writing to a pin

Set to high:

gpioset -c 0 --toggle 0 16=1

Set to low:

gpioset -c 0 --toggle 0 16=0

Reading the logical level from a pin

gpioget -c 0 16

ADC

i.MX91 SoC features integrated 12 bit analog to digital converter.
To use the ADC, enable it in device tree e.g. in arch/arm64/boot/dts/compulab/sbc-mcm-imx91.dts:

&adc1 {
       vref-supply = <&reg_vref_1v8>;
       status = "okay";
};

Sysfs device controls will appear in:

cd /sys/bus/iio/devices/iio\:device0/

SB-UCMIMX91 exposes ADC signals on 100-mil header P3.

Signal Name	pin on P3	sysfs file
ADC_IN0	9	in_voltage0_raw
ADC_IN1	11	in_voltage1_raw
ADC_IN2	13	in_voltage2_raw
ADC_IN3	15	in_voltage3_raw

For example, to read voltage from P3-9 run:

cat /sys/bus/iio/devices/iio\:device0/in_voltage0_raw

Expected output is a value in range 0 - 4095 which spans over the voltage range 0 - 1.8V

Suspend / Resume

The operation below requires root access.

• Suspend mode allows minimizing the power consumption.
• To enter suspend mode run:

echo mem >/sys/power/state

• To resume normal operation press shortly the power button SW5.
• To enter suspend mode with RTC as wakeup source that wakes after 5 seconds run:

rtcwake -s 5 -m mem -d /dev/rtc0

• WiFi device currently doesn't support suspension. see UCM-iMX91:_Yocto_Linux:_Known_Issues

CPU temperature

i.MX91 SoC features an internal temperature sensor which allows to measure the SoC temperature. Execute the following command to read the current CPU temperature:

cat /sys/class/thermal/thermal_zone0/temp

RTC

UCM-iMX91 features two RTC devices:

• i.MX91 internal RTC (rtc0) - can be used as wake-up source
• AB1805 external RTC (rtc1) - can be used for low current battery powered time keeping

Internal RTC - rtc0

System information:

udevadm info -p /sys/class/rtc/rtc0

P: /devices/platform/soc@0/44000000.bus/44440000.bbnsm/44440000.bbnsm:rtc/rtc/rtc0
N: rtc0
L: -100
S: rtc
E: DEVPATH=/devices/platform/soc@0/44000000.bus/44440000.bbnsm/44440000.bbnsm:rtc/rtc/rtc0
E: DEVNAME=/dev/rtc0
E: MAJOR=251
E: MINOR=0
E: SUBSYSTEM=rtc
E: USEC_INITIALIZED=14959708
E: DEVLINKS=/dev/rtc

Wake up:
rtc0 can be used as a wake up source, as a result an rtcwakeup can be used with this device:

rtcwake --device /dev/rtc0 -s 5 -m mem

External RTC - rtc1

System information:

udevadm info -p /sys/class/rtc/rtc1

N: rtc1
L: 0
E: DEVPATH=/devices/platform/soc@0/44000000.bus/44340000.i2c/i2c-0/0-0069/rtc/rtc1
E: DEVNAME=/dev/rtc1
E: MAJOR=251
E: MINOR=1
E: SUBSYSTEM=rtc

Set the date and write it into the RTC:

date -s "16 Jun 2023 12:00:00"

Fri 16 Jun 2023 12:00:00
hwclock --systohc --rtc /dev/rtc1

Read the RTC time and date:

hwclock --show --rtc /dev/rtc1

2023-06-16 12:01:37.915876+00:00

Device Serial Number

Product information is stored in on-board EEPROM.

• To read the product serial number run:

cat /proc/device-tree/product-sn && echo

• To read the product configuration part number run:

cat /proc/device-tree/product-options && echo

See Also

• Eval-kit Quick Start Guide
• Eval-Kit Hardware Guide