We have an iMX287 based platform, heavily inspired by the iMX28 EVK. One DDR2 memory, ISSI, IS43DR16640B-25DBLI.
I have spent the last 4 weeks chasing a problem in this platform. It would be a very, very long story to cover everything that has been done.
This is the summary:
5V only, no battery. Hardware exactly according to the PMU White paper for 5V only operation.
Originally we run uBoot + Yocto Linux.
We also tests "latest" LTIB with Freescale bootlets instead of uBoot.
The platform has worked for 1 year during development without any problems at all. Then, when we tested the platform in our temperature chamber at -20 degrees Celsius we observe the following:
*With uBoot based firmware: SPL boot works fine, but when all "relocating" stuff runs, the entire power system shuts down. The 4P2 turns off and thats it. Reset dosn't work, only a 5V power cycle and a cold start.
*With bootlet+LTIB, initial startup works OK, uncrompressing kernel works OK, but exactly same power shutdown just after "Starting kernel" console message appear. The problem is 100% repeteable in -20 degrees C. In room temperature kernel boots OK in 99.99999% of all cases.
We have spent Days/weeks checking DDR2 settings, tested different DDR2 settings, no change at all. We have logged ALL supply rails, both 5V and the iMX generated ones with a 50MHz analogue data logger. Looks ultra clean, no glitches, ripple or anything. It appears as the PMU simply turns off power and dies.
10+ boards tested with exactly same behaviour, different iMX287 batches also.
I have our boards stripped down to contain only iMX287, DDR2, decoupling caps, console terminal and USB connector for sb-loading. No other stuff on the board.
I have checked the current waveforms on the 5V feeding rail to the iMX with a 50MHz LEM probe. No "strange" spikes or anything before the shutdown. It simply shuts down and dies.
One interesting observation has been made last week: If I test the board in room temperature it appears as everything is working OK. But when I add a small 51 ohm resistor on the 1.8V DDR2 voltage rail, I get 100% boot failure as described above. Same if I add the load on the 3.3V rail.
I believe I have tried disabling all brownout, maxing current limiters etc. etc. etc. but with no improvement. We have been ALL over the Place with theories, memory failures, PCB issues but everything appears to check out OK.
I can't understand what is causing this. How can I narrow down what causes the PMU to make the decision to shutdown? I'm running out of ideas totally.
All feedback is more than welcome.