Is there any option to identify the port, of iMX-53 chip, which was
selected for download during system boot in serial mode?
USB-OTG or UART1-5 will be selected if any has bus activty. Please refer RM 7.8 Serial Downloader (BOOT_MODE[1:0] = 0b11) for detail.
I know that, and my problem is to define which port was really captured for downloading. I suppose, that some 'wrong' port performs unsuspected activity before the desired port had to do, becuase I have several boards, slightly different in hardware, but with great difference in bootloader behaviour.
I guess you can attach the board using JTAG tool dump the uart_status_reg_2 of the uart modules one by one, the ROM will select the first one which uart_status_reg2[RDR] bit set as the boot port.
That was the first I did
The real problem was that USBOTG was the source of the problem, so UART regs were all silent.
Be careful with schematic, if ESD protection diodes are not powered at cathodes but slightly loaded (e.g. with LED for USB power availability indication), the data pins are also loaded through p-n junction of ESD diode and iMX recognize it as an USB port serial downloader actibity...
I am a little bit confused. You meant that your board boot from USB-OTG even no USB cable connected(to confirm this, please dump USB_OTG_USBSTS) [BIT6], if it set, the ROM will boot from USB) to PC and this is caused by ESD diodes, right?
If yes, I guess it is a HW issue. I never met such issue on FSL reference board.
My little knowledge about USB protocol tells me that USB activity is detected not with the cable itself, but with some activity in DP/DM pins. Generally, it starts with some pulling of USB data lines to define the USB protocol type. I fixed the problem with elimination of power indication LED, that resulted in release of DM/DP pins from any external loading, when no USB connection exists.
In Freescale reference board iMX53QSB (e.g.), the USB ESD protection cathodes are tied to non-switcheable 5V main power supply bus, so no any leakage can exist when board is powered on. In my case, the USB power is switcheable (why I used the separated LED for indication of its availability). In next board revision, I will re-route this net to avoid the problem.
Thank you a lot for assistance!
I am also experiencing some issues with the Serial download as my board is working intermittently.
Is it really that sensitive for iMX53 to detect any activity on any of the UART ports or the OTG port?
Is it a must not to connect anything onto the unused UART receiver pin so as to avoid iMX53 locking up the wrong port for serial download? Must we pull up or pull low the unused Rx pins?
And what should we do with the USB OTG port if it is not to be used as the port for Serial download? I had left the DP/DM pins floating but I am still getting problem from time to time which my board is not responding with my host when my host is sending the GetStatus command. I am suspecting wrong port was connected.
Thanks & regards,
Retrieving data ...