Boot Setup

The G3 module can be booted from one of three sources:

  • SD card

  • eMMC (flash)

  • USB OTC1,2

Note

The first time an eMMC or SD card image boots, the system will automatically extend the data partition to use all available space. In eMMC this will result in the /data filesystem being approximately 4.5GB in size. On SD cards, the final size is, of course, dependent on the size of the SD card.

The expansion is a two step process:

  • On the first boot, the data partition3 is expanded; once complete the G3 module automatically reboots to ensure the kernel recognizes the larger partition.

  • After the reboot, the /data filesystem is resized to fill the expanded partition; once complete, the G3 module continues a normal boot sequence until it displays the login prompt.

Important

The G3 module includes a number of optional services, several of which are enabled by default, including the sshd secure shell server. The first time a new eMMC or SD card image fully boots, the init script for sshd generates a unique set of host keys in several formats. This takes some time. More importantly, you must make sure the new key files have been flushed to the SD card prior to halting or rebooting the G3 module. The simplest way ensure this is to login as root at the prompt and issue the sync command.

Footnotes:

1

Booting over USB is not available on all G3 module variants.

2

Booting over USB is impractical for most field applications so it’s not documented here. Contact Reach Technology Technical Support if you really need to do this.

3

The data partition is the last partition in the image. For i.MX6 based boards that use the older DOS style partition table, this is partition 4. The STM32MP157 based boards use a GUID partition table so the data partition is partition 7 on those boards.

Important

From a strict system reliability perspective, we recommend using the eMMC as the boot device for field-deployed systems. However, using the SD card will likely be simpler to manage during the product development process.

In some cases, a hybrid solution may make sense. For this type of system, you would use eMMC for the O/S and the SD card for the end product application.