Hello,
we are tying to bringup a new custom board based on the beaglebone black. I have a functional TI-Arago based uSD which does work on the BBB, as well as a previous version of our board.
However, for some reason the uSD does not boot on our new system. We see "CCCCCCCCC" over UART0 at boot without a uSD card installed since the eMMC flash is currently erased. If we turn on the system with a uSD card installed, we get no UART output at all. We can tell the ARM is still alive as it is drawing a normal amount of current for operation.
We have put the old board and the new board next to each other each with a uSD installed, then power both up simultaneously with o-scope probes on the same lines so we can see differences between the MMC lines. What we see is the the "Command" signal for the old board is logic high always, on the new board it looks like a data bus and is totally different.
Also, we noticed that the clock on the old board runs longer than the new, where the new one seems to quit after about ~300 to 400mS.
We have verified the boot strap resistors are installed properly. Also all the MMC signal lines appear to be connected to the appropriate pads on the ARM.
We are at a total loss as to whats going on!
Are there any suggestions you might make to troubleshoot this issue?