This topic explains how to boot Digi Embedded Yocto images without updating the firmware on the internal eMMC. This is helpful during the development phase, as it preserves the original firmware on the SOM.

Open a serial connection

You must open a serial connection to communicate with your device.

  1. Open a serial connection using any terminal program such as Tera Term, Minicom, Coolterm, or HyperTerminal. This documentation demonstrates using Minicom to work with the device command line.

    Use the following settings:

    Parameter Value

    Port

    Serial port where the device is connected

    Baud rate

    115200

    Data bits

    8

    Parity

    None

    Stop bits

    1

    Flow control

    None

  2. Reset the device by pressing the reset button on the board. Then immediately press any key in the serial terminal to stop the auto-boot process. The U-Boot bootloader prompt displays:

U-Boot SPL dub-2020.04-r2.2 (Jan 18 2021 - 15:54:36 +0000)
DDRINFO: start DRAM init
DDRINFO: DRAM rate 3000MTS
DDRINFO:ddrphy calibration done
DDRINFO: ddrmix config done
Normal Boot
Trying to boot from BOOTROM
image offset 0x0, pagesize 0x200, ivt offset 0x0


U-Boot dub-2020.04-r2.2 (Jan 18 2021 - 15:54:36 +0000)

CPU:   i.MX8MNano Quad rev1.0 1400 MHz (running at 1200 MHz)
CPU:   Industrial temperature grade (-40C to 105C) at 36C
Reset cause: POR
DRAM:  1 GiB
MCA:   HW_VER=1  FW_VER=1.01
MMC:   FSL_SDHC: 1, FSL_SDHC: 0
In:    serial
Out:   serial
Err:   serial
Model: Digi ConnectCore 8M Nano Development Kit
ConnectCore 8M Nano SOM variant 0x01: 1 GiB LPDDR4, Wi-Fi, Bluetooth, MCA, Crypto-auth
  Board version 3, ID undefined
Boot:  MMC2

 BuildInfo:
  - ATF 9447098
  - U-Boot dub-2020.04-r2.2

flash target is MMC:0
Net:   eth0: ethernet@30be0000
Fastboot: Normal
Normal Boot
Hit any key to stop autoboot:  0
{pu}

Boot the system from network

This shows how to transfer the images to the target via TFTP or NFS, and mount an NFS root file system.

This requires that you set up your PC workstation as explained in Set up your development workstation.

1. Prepare the device artifacts

  1. Get the Yocto firmware images to boot from network:

    • <kernel-file>.bin

    • <device-tree-file>.dtb

    • <rootfs-file>.rootfs.tar.bz2

    1. After building the Yocto firmware, you can find the image files inside the project directory at:

      <project_folder>/tmp/deploy/images/<platform>

    2. You can download Digi provided pre-built images from:

  2. Untar the root filesystem tarball (*.rootfs.tar.bz2) in the NFS exported directory of your development workstation. See Set up your development workstation.

    ~> sudo tar xvfp image.rootfs.tar.bz2 -C /exports/nfsroot-ccimx8mn_dvk

  3. Copy the kernel *.bin file to the TFTP exported directory of your development workstation.

    ~> sudo cp image.bin /tftpboot

  4. Copy the device tree *.dtb file to the TFTP exported directory of your development workstation.

    ~> sudo cp image.dtb /tftpboot

2. Configure your device’s network settings

  1. Get a dynamic IP for your target:

    => setenv autoload no
=> dhcp

    or you can set a static IP:

    => setenv ipaddr 192.168.115.222

  2. Configure the IP of the development workstation with TFTP and NFS servers installed. See Set up your development workstation:

    => setenv serverip 192.168.115.1

3. Boot from network

Boot from TFTP+NFS

  1. Set the directory with the rootfs to mount. This directory is the one exported via NFS in your development workstation. See Set up an NFS server.

    => setenv rootpath /exports/nfsroot-ccimx8mn_dvk

  2. Specify the device tree (*.dtb) file name. This is the name of the *.dtb file you copied to the TFTP exported directory of your development workstation.

    => setenv fdt_file image.dtb

  3. Establish the kernel file (*.bin) name. This is the name of the *.bin file you copied to the TFTP exported directory of your development workstation.

    => setenv imagegz image.bin

  4. Save the changes.

    => saveenv

  5. Boot from TFTP.

    => dboot linux tftp

    You can make these changes persistent by writing the following command:

    => setenv bootcmd 'dboot linux tftp'
=> saveenv

The target now loads the kernel and device tree from the TFTP server and the root filesystem from the NFS server.

Boot entirely from NFS

To avoid using TFTP for kernel and device tree files and boot everything from NFS, copy the kernel *.bin and device tree *.dtb files to the NFS-exported directory of your development workstation (instead of to the TFTP directory). See Set up an NFS server.

=> dboot linux nfs

Boot from microSD card

U-Boot can start a complete Yocto system from a microSD card. To boot a system from a microSD card, follow these steps:

1. Create a bootable microSD card from a Yocto image

Requirements:

  • Root/Administrator permissions in your development computer

  • A microSD card with a minimum capacity of 2 GB

The following procedure will destroy existing data in the microSD card.

To create a bootable microSD card from an existing Yocto image:

  1. Download the bootable Yocto image from this URL: https://ftp1.digi.com/support/digiembeddedyocto/2.6/r3/images/ccimx8mn-dvk/xwayland/.

  2. Extract the .sdcard file from the zip you downloaded into a folder of your choice.

  3. Insert the microSD card into your computer and check the node Linux assigns to it (/dev/[sdcard]) using dmesg:

    $ dmesg
[1413652.901270] sd 41:0:0:0: [sdc] 7744512 512-byte logical blocks: (3.96 GB/3.69 GiB)
[1413652.903140] sd 41:0:0:0: [sdc] No Caching mode page present
[1413652.903144] sd 41:0:0:0: [sdc] Assuming drive cache: write through
[1413652.905638] sd 41:0:0:0: [sdc] No Caching mode page present
[1413652.905642] sd 41:0:0:0: [sdc] Assuming drive cache: write through
[1413652.915154] sdc: sdc1

    Do not mount any partitions the card might contain (or unmount any partition if automatically mounted) as you will be writing to the entire block device.

    Using an incorrect device node in the next step might destroy all data on your computer hard drive.

  4. Raw write the image file to the microSD card with this command:

    sudo dd if=<path/filename.sdcard> of=/dev/<sdcard> bs=64K && sync

    In this example:

    • You must substitute <path/filename.sdcard> with the path and filename to the SD card image.

    • You must substitute <sdcard> with the device node Linux assigned to your microSD card.

The microSD card is now ready.

2. Boot Yocto from the microSD card

  1. Power off the device.

  2. Insert the microSD card into the microSD card holder (bottom side of the board).

  3. Change the boot source configuration to boot from the microSD card. To do so, set the boot mode micro-switches as follows:

    • S1.1: OFF

    • S1.2: ON

    • S1.3: ON

    • S1:4: N/A

      microSD boot

  4. Power on the device. Digi Embedded Yocto boots from the microSD card.