Uboot too fast and USB host read timeouts

[thomaslantinga]

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:

1. uBoot seems to run faster than on the other boards, about 3 times faster.
2. After a cold start the USB stick at the USB host port of the i.MX6 is not always recognised.
3. 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.

[igorpadykov]

Hi Thomas

one can attach jtag debugger or using uboot commands and output

arm clock on CCM_CLKO1,2. Program CCM_CCOSR register

and measure frequency arm_clk_root, osc_clk. In general chip

can be damaged due to ESD or overheating.

Best regards

igor

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