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?
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!