We made a small production serie of 10 PCBA's with a i.MX6D based on a custom design.
This board has a dedicated USB host (i.MX6 host port) and USB device (i.MX6 OTG port) connection.
9 boards are working fine, but on one board we see 3 problems:
- uBoot seems to run faster than on the other boards, about 3 times faster.
- After a cold start the USB stick at the USB host port of the i.MX6 is not always recognised.
- When the USB stick do get recognised, we get read timeouts when we try to access the data.
Problems 1 and 2 seems to be dependant on the board temperature. When the temperature rises, uBoot seems to slow down a bit, but still faster than on the other boards. The USB stick now gets recognised all the time. But still read timeouts.
Things I have checked:
- 24MHz crystal is stable and at the right frequency, at cold startup and after couple hours.
- Power supplies are all in the right range and ripple is less than 5%.
- I saw that the LDO_2P5 had a saw tooth voltage ripple which was near 5%. Followed the EB814 document on minimum ESR requirements, placed a 100mOhm resistor is series with the bulk capacitor of de LDO_2P5 regulator. The saw tooth voltage ripple disappeared. But no change in the behaviour of the board.
- No USB problems detected on the i.MX6 OTG port in device mode
I am out of ideas now, so if any of you have suggestions, please let me know.