06-14-2020, 02:24 PM
Is there a trick to logging into the wiki? I thought it was just the forum username/password, but that doesn't work.
As I understand the boot process, per some conversations on IRC and experimenting:
The mask ROM code runs first. This searches for a uboot binary in SPI, on eMMC, and finally on the SD card. It will execute the first one it finds - which is why if you screw up the eMMC, the SD card doesn't work.
The uboot path then loads the remaining bits as needed, and will look for a kernel to boot - in a configurable, and perhaps different, order. Typically these search for the SD card first, but it's not guaranteed.
The safe way to mess around is to have nothing on the eMMC (either wipe the first... oh, 16MB ought to do it, or just remove/disable it), and do all your work on the SD card. At this point, you can't screw up anything you can't fix trivially in an external machine. You'll probably want to enable the UART while you're inside and build an adapter for boot messages.
As I understand the boot process, per some conversations on IRC and experimenting:
The mask ROM code runs first. This searches for a uboot binary in SPI, on eMMC, and finally on the SD card. It will execute the first one it finds - which is why if you screw up the eMMC, the SD card doesn't work.
The uboot path then loads the remaining bits as needed, and will look for a kernel to boot - in a configurable, and perhaps different, order. Typically these search for the SD card first, but it's not guaranteed.
The safe way to mess around is to have nothing on the eMMC (either wipe the first... oh, 16MB ought to do it, or just remove/disable it), and do all your work on the SD card. At this point, you can't screw up anything you can't fix trivially in an external machine. You'll probably want to enable the UART while you're inside and build an adapter for boot messages.