Bootloader

Boot Scenarios

• Boot device is the eMMC or NAND flash provided on the module. U-Boot, kernel and rootfs are stored on the boot medium. The U-Boot environment in our images is set for this scenarios.
• Boot device is a SD card. U-Boot, kernel and rootfs are stored on the boot medium. The strapping pins have to be set accordingly (Colibri T20/T30 only).
• By changing the U-Boot environment the storage location of the kernel and rootfs can be changed to something different than the boot device.
• The kernel can be loaded from eMMC/NAND flash, SD card, USB memory stick or a TFTP server.
• The rootfs can be on eMMC/NAND flash, SD card, USB memory stick or a NFS server.

Common Combinations

• Everything on eMMC/NAND flash –> Regular production and testing use.
• Everything on SD card -> When you want to change between different OS', i.e. WinCE on eMMC/NAND flash, Linux on SD card (Colibri T20/T30 only).
• U-Boot on eMMC/NAND flash, kernel and rootfs on SD card -> When you want to change between different kernels / rootfs'.
• U-Boot on eMMC/NAND flash, kernel from TFTP and rootfs from NFS -> During kernel and application development and debugging.

See the release notes of our Linux image for instructions on how to activate eMMC/NAND flash or SD card boot on a Colibri T20/T30. For the other scenarios the U-Boot environment of a module that either does eMMC/NAND flash or SD card boot is modified as described below.

Reference

https://www.denx.de/wiki/DULG/UBootEnvVariables