That means that when the SD is inserted, there is no need to flash a special rom to boot an alternative kernel/Linux/Android flavour.
See http://androtab.info/radxa_rock/sdboot/
Now that said... I have not gotten it to work properly.
What I found so far is that on my T428 I can boot with the files in the http://files.androtab.info/radxa/sdb...8_miniroot.zip package, but then replacing the kernel with a kernel for my stick. Using the Radxa kernel will just show a black screen.
Using the picbuntu kernel file, I do see the boot messages, and I end with an error that it can't find the root device and it is dropping me to the command line. From there I can connect to the network with the minimalistic commands that are available. However with the picbuntu kernel I still get lots of errors in the booting process. Specifically it seem to have difficulty reading the remainder of the sdcard.
The key now is to make a proper working package that is easy to use. Hope that anyone has good suggestions on how to move forward.
what i also found;
When the parameter file is edited directly it will not boot anymore from the SD card, it will hang somewhere prior to the kernel loading. You can modify the parametere file, but it requires it to be signed again.
You can sign it by using the rkrc command from the rk-tools https://github.com/rk3066/rk-tools. Then it will be usable for flashing.
To create the SD I used this little batchfile to avoid typing the commands each time
#!/bin/sh DEV="/dev/sdb" LOADER="sdboot_rk3188.img" PARA="parameter.img" KERNEL="kernel-pic.img" BOOT="boot.img" echo "SD disk preparation" echo "device $DEV" echo "loader: $LOADER" echo "parameter: $PARA" echo "kernel: $KERNEL" echo "boot: $BOOT" echo "Copying loader: $LOADER" sudo dd if=$LOADER of=$DEV conv=fsync echo "Copying parameter: $PARA" sudo dd if=$PARA of=$DEV conv=fsync seek=$((0x2000)) echo "Copying kernel: $KERNEL" sudo dd if=$KERNEL of=$DEV conv=fsync seek=$((0x2000+0x4000)) echo "Copying boot: $BOOT" sudo dd if=$BOOT of=$DEV conv=fsync seek=$((0x2000+0xC000))
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