[MinnowBoard] Boot MinnowBoard Max from SD using U-Boot

[Philipp, Damian]

Hello Minnowboard Gurus,

after finally receiving my SPI Hook, I have taken on the task of flashing my MinnowBoard Max with a new bootloader. My goal is to have a bootloader that can do both Netboot/PXE as well as boot from SD. To avoid confusion: The normal usecase will be to do automatic booting via network. However, I want to keep the option of booting from SD in case I am away from my usual setup, i.e., don't have access to my Netboot service.

I managed to compile u-boot v2016.03 using the 0.90 Minnowboard Max firmware (make defconfig_minnowboard) and have successfully flashed that using the SPI Hook. However, I cannot get U-Boot to recognize my SD card. The SD card I am using has been prepared as an EFI bootable card (ext4, fat, swap partitions) and works flawlessly using the Intel UEFI firmware. While this *might* be the wrong format, I would still expect to be able to load the kernel from the FAT partition. However, when I start U-Boot, "mmc list" tells me that there are no MMC devices present. In contrast, loading and starting a kernel over the network does work. However, that kernel is currently configured to find its root filesystem on the SD card (i.e., I copied it from the SD card to my tftp server). In this experiment, the Kernel never finds the root device.

I suspect that I am missing some configuration options for U-Boot to properly enable SD card support. Sadly, using U-Boot to boot the MinnowBoard Max from MMC does not appear to be a very common usecase, as Google  did not give me any useful hits. What do I have to do to enable SD boot on my MinnowBoard using U-Boot?

Thank you in advance
Damian Philipp

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Software Development Engineer
PES

Vector Informatik GmbH
Ingersheimer Str. 24
70499 Stuttgart
Deutschland / Germany
Tel.: +49 711 80670-3656
Fax: +49 711 80670-399
mailto: Damian.Philipp at vector.com
Internet: www.vector.com

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