Booting

While not an absolutely necessity, a bootloader such as UBoot is nice to have, mostly so that we can load binaries to test over serial or Ethernet instead of having to remove the SD card, write files, and re-insert the card every time we update the code. It may also be possible to add one of these transfers as a target in our Makefile for added convenience.

FreeBSD developer Oleksandr Tymoshenko (blog) has been working on porting UBoot to the Pi. The current binary in use is here. The instructions to install it are as follows:

• Download Raspian
• dd if=<raspian-image> of=<sd-card-dev> bs=2M
• Extract the UBoot .tar.gz into the boot partition
• Connect serial device/monitor and boot the Pi

To load Raspian:

• fatload mmc 0:1 0x00200000 kernel.img (loads the Raspian kernel)
• bootz (boots zImage binaries)

To [possibly] load Xinu:

• fatload mmc 0:1 0x00200000 xinu.elf
• bootelf

Currently, nothing interesting happens when we try to boot Xinu. This may be an issue with how we're loading the binary into memory or something more subtle.