iMX6: Debug UART at ROM level?

[EgleTeam]

Hi,

Do any of  iMX6 UART ports is configured by default for debugging while ROM code is executed?. I mean: something like in other families (i.e: iMX28) where one of the UARTs can send  ROM error codes before loading uboot.

If not: Is there any alternative way for debugging before loading uboot?.

Thanks & regards,

Manuel.

[Yuri]

I.MX6 boot ROM supports only USB as serial bootloader, UART is not supported as for other i.MX parts.

(I mean boot_mode = 01 Serial Downloader). Next, only i.MX28 / 23 provide boot ROM messages
to the Debug UART. This feature does not take place for the other i.MX devices.  

[EgleTeam]

Thanks Yuri,

so... with the boot pins configured for "internal boot mode", USB-OTG cable connected to a PC and mfgtool running:

1. If nothing happens: there's something fundamentally wrong on the SoC and/or supply rails.

2. If the Soc connects to the mfgtool: ROM can't boot from selected device by the GPIOs.

Please correct me if the above approach is wrong.

We look for a quick way to know the reason if our custom board (finishing the design) doesn't boot the OS at the first attempt.

Regards,

Manuel.

[Yuri · Accepted solution]

Just as a  test, if a (Windows) USB insertion activity occurs (somewhat as new device found),
when i.MX6 board is connected. If - yes - this good sign, we can hope to run the MFG.
If - no, system cannot start, try standard bring up procedure. 

[EgleTeam]

Hi,

finally we have our hardware fabricated with iMX6 DualLite installed. Unfortunately we can't bring up the boards. Windows can see an USB device connected but can't get VID & PID. Clock and all power domains are OK.

On the other hand, we have tried to boot Android and Ubuntu prebuilt images on a SD port. We can see how Windows don't see the USB OTG port when a valid SD card is inserted, as well as we can see activity on the CLK line with a scope as well as different power consumption in Ubuntu and Android: what make us think that the iMX6 begins to read uboot but fails in some point. Unfortunately we can't see anything on the UART port.

Does uboot begin to send messages over the debug UART port all along or first checks any critical hardware (i.e.: DDR3)? What do you recommend us in order to find what is going wrong?

Best regards.

[EgleTeam]

Our mistake: we were testing with Android & Ubuntu images for Quad core. The uboot image for DL boots right. SOLVED.

USB OTG still being not recognized when there's no another boot device but this is not important right now.

Best regards,

Manuel.

[EgleTeam]

Thanks Yuri!