Debugging problem with GPIO serial pins

Question

I've been trying to run a port of a small RTOS called ChibiOS on my Raspberry Pi, and am having trouble with the serial communications. Specifically, when I use a UART connected at 3.3V to the GPIO pins on the Pi, I can receive Tx from the Pi but it won't respond to anything sent over the Rx line. I saw on http://forum.chibios.org/phpbb/viewtopic.php?f=2&t=1334 that my problem could be due to using a faulty new release of bootcode.bin or start.elf and tried the version recommended on that forum, but it didn't work. I was wondering:

1) Is there somewhere I could get the source code to bootcode.bin or start.elf to examine, and then compile them myself? This might help me with debugging my problem.

2) What are some things I can do in order to better debug my problem?

EDIT:

3) Are there any similar situations you have experienced involving a nonfunctional Rx line which might point me toward the problem?

Thanks for taking the time to answer!

Answer 1

For both bootcode.bin and start.elf, as best I can, source still isn't public. While I wasn't able to find it explicitly stated, they appear to still part of the remaining "blob" talked about in the rasp pi birthday post, though if you want to do a deep-dive broadcom's bcm21553 driver release might have the parts you could build your way there.

There are a number of projects hinting at it:

• Unsure how complete the information is but Herman Hermitage github seems to have a bunch of info in that space (Lots of other sources point to that as the home of a reverse eng effort on Videocore CPU code, of which I believe bootcode.bin and start.elf are)
• In the same "unsure" place there is the piface tool, the docs make it clear the tool isn't very functional at this point, but it at least beings the process of opening up the Videocore CPU