Best overall documentation I could find is Derek Malloy's "Exploring Beaglebone" textbook. It was relatively cheap bought for Amazon Kindle and is an amazing resource for the things I want to do. Yet it was written a while ago and some (many?) things have changed since it was written.
https://www.mouser.com/pdfdocs/BBG_SRM_V3.pdf is a good reference on how BBGW is intended to work. It doesn't tell you much about how it does what it does, or how to change it. I believe there is no documented way to switch boot order to favor sdcard over u-boot other than the boot button. https://www.linuxjournal.com/content/handy-u-boot-trick is a good article on some ways to change u-boot rules but as the title suggests it's more of a "u boot trick" than a standardized way to switch boot order such as a boot manager. I booted my board using the u-boot on eMMC then used u-boot commands on the serial port to boot my linux from sdcard. The linux I booted was the yocto build that the textbook above described how to build. See my notes below. This may be enough to get you going? I'd like come up with a way to select an image via the debug serial port. Some sort of boot manager / image selector like grub is for the x86 world. But I haven't spent any time investigating that path. Here are my notes. => ext4ls mmc 0:2 /boot <DIR> 4096 . <DIR> 4096 .. 58296 am335x-boneblack.dtb 56480 am335x-bone.dtb 6785592 zImage-5.2.17-yocto-standard 56736 am335x-bonegreen.dtb <SYM> 28 zImage => setenv loadzimage "load mmc 0:2 ${loadaddr} /boot/zImage" => setenv loadftd "load mmc 0:2 ${fdtaddr} /boot/am335x-boneblack.dtb" => setenv bootargs "console=ttyO0,115200n8 root=/dev/mmcblk0p2 ro rootfstype=ext4 rootwait fixrtc ${optargs}" => run loadzimage 6785592 bytes read in 459 ms (14.1 MiB/s) => run loadftd 58296 bytes read in 24 ms (2.3 MiB/s) => bootz ${loadaddr} - ${fdtaddr} ## Flattened Device Tree blob at 88000000 Booting using the fdt blob at 0x88000000 Loading Device Tree to 8ffee000, end 8ffff3b7 ... OK Starting kernel ... On Friday, December 27, 2019 at 11:12:12 AM UTC-5, StefanO wrote: > > > Hello all, > I like to change the boot order on my BBGW device. > > At the moment, if I power on it boots from the internal eMMC Card, if a > external storage Card in inserted, or not. > I have to press the the boot button during boot time to force a start with > the external Card. > > I like to have it the other way: > If a valid external SD is fund, it will boot from this, other wise it will > boot from internal eMMC. > How do I do this? > Is there a documention about the boot process and disk partitions > somewhere, so I can find out by myself? > > thank you in advance > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/f09e7d4e-1954-4001-8b34-8561bbbb2f0a%40googlegroups.com.
