I've designed a module based on the QSB, with a Ripley PMIC but otherwise generally following the original QSB schematic. (The Ripley version wasn't available when I did the schematic.) I'm booting from SD and when it boots everything seems perfect; u-boot runs, Linux loads and runs from the SD, a memory test passes, the display, ethernet and USB are OK and all the relevant tests in the "unit_tests" directory pass.
The problem is that most of the time it fails to boot. Repeated on/off cycles will eventually get it going, but usually it just crashes with no output on the serial port and no response to serial commands.
It must be a hardware problem, because the same SD card always boots correctly on the QSB but I'm struggling to work out why. The power rails, clock and reset seem OK, and when it does boot there are no signs of anything flaky. Has anyone seen a similar problem, or have any ideas what might be going wrong?