For I workshop we had to use dd to write zeroes to the typical location of uboot. That would be breaking the uboot partition.
Note that uboot is very flexible. It has some useful predefined variables through which you can easily configure booting. For example, uboot just calls: run bootcmd. So if you set bootcmd to match your wishes, you will have the booting behavior you want. I typically use: run netboot. That's defined by default and I set all other variables to make the netboot run as I please. Don't forget saveenv. http://etutorials.org/Linux+systems/embedded+linux+systems/Chapter+9.+Setting+Up+the+Bootloader/9.5+U-Boot/ There is are also options to scan for possible bootable partitions, but I don't know the details. I have not seen uboot present any menu like grub does. Op ma 6 jan. 2020 21:53 schreef David Cherkus <[email protected]>: > Is there a workable way to "corrupt" the MLO in eMMC so the first level > program loader in ROM skips over it and tries sdcard instead? > > On a board I used to work on the ROM looked for a magic number at the > start of each flash sector and if you overwrote the magic number with 1s > (i.e. erased the sector) it would not use the flash and would fail over to > trying removable media. > > This let us come up with a scheme to store the intentionally corrupted > boot sector elsewhere on the flash when we wanted to boot to external media > then restore it (with the correct magic number) when we wanted to boot from > flash. > > Another scheme as above would be to always boot using eMMC's MLO and > u-boot.img then use rules in eMMC's /boot/uEnv.txt that establish the > default bootcmd and provide alternates you can use to override the default > bootcmd as needed to pull linux and device tree from whatever source you > prefer (sdcard, tftp, nfs, etc). > > On Friday, December 27, 2019 at 12:00:58 PM UTC-5, RobertCNelson wrote: >> >> On Fri, Dec 27, 2019 at 10:12 AM StefanO <[email protected]> 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 >> >> There is a spec, which is used by default.. >> >> >> https://elinux.org/Beagleboard:U-boot_partitioning_layout_2.0#uEnv.txt_Rootfs_Partition_.2Fboot.2FuEnv.txt >> >> but if your using a custom u-boot, then it's probably not enabled.. >> >> Regards, >> >> -- >> Robert Nelson >> https://rcn-ee.com/ >> > -- > 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/1c1b29d7-b850-4526-b958-7e5a7bf1101c%40googlegroups.com > <https://groups.google.com/d/msgid/beagleboard/1c1b29d7-b850-4526-b958-7e5a7bf1101c%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- 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/CAHK0gJ3-NfzbCvj_Lt3EU11QdMyps4O7tS6qGKmH6nV%2BL2FRXg%40mail.gmail.com.
