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Workaround for unreliable boot from SD?

Question asked by Ian Kalinowski on Sep 23, 2013
Latest reply on Oct 1, 2013 by Naoum Gitnik

I've been testing a TWR-VF65GS10 Rev. G board built with the full tower (main board + TWR-SER2 module + TWR-LCD-RGB module) and noticed that the board boot ROM does not reliably boot from the SD card on each reset.  I'm using the 4GB SanDisk MicroSD card that came with the board.  I have both the micro-USB port on the main board (J3) and the mini-USB connector on the primary elevator board attached to my development machine to power the system.  Once every 15-20 cold power cycles (by toggling the power switch on the primary elevator board), the board fails to run U-Boot from the SD card.  The same failure also occasionally occurs when pressing the reset button on the main board or when using a hardware debugger (attached to the 20-pin JTAG connector) to issue a warm reset.  I haven't noticed any difference in the frequency of the failure between cold and warm resets.  This behavior occurs regardless of whether the JTAG hardware debugger is attached to the board, but when the JTAG debugger is attached, I can see that the PC is at an address within the boot ROM (e.g. PC=0x000030c0 or 0x00006ba6) after the failure occurs.  We've had two engineers both independently discover this issue on different boards so it doesn't appear to be a problem with one particular board.  Is there a workaround for this issue that will allow us to reliably boot from the SD card?