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Boot mode in IMX8M

Question asked by Jemish Patel on Dec 20, 2018
Latest reply on Mar 21, 2019 by Ray Mack

Hi All,

 

We are going to make product based on IMX8MQ (MIMX8MQ6DVAJZAA) processor.  Currently we are doing POC on IMX8MQ processor EVK.

 

  • While understanding booting process from Technical Reference Manual we understand that if boot process failed to boot from configured device it will jump to boot from USB serial mode. There is NOTE in Technical Reference Manual regarding this:
  • NOTE
    Before going into USB serial mode, Boot ROM detect
    SD/MMC card on USDHC1 port. If a card is inserted, ROM
    will try to boot from it. This is the so-called Manufacture
    SD/MMC boot. This feature can be disabled by blowing fuse
    “Disable SD/MMC Manufacture Mode”. 

 

  • In IMX8MQ EVK there is an eMMC connected  to USDHC1. There is SD card connected to USDHC2. 
  • We prepared bootable SD card.  We set SD boot mode and board get booted from SD which is correct. Then we clear eMMC boot partition using following command:

        echo 0 > /sys/block/mmcblk0boot0/force_ro
         dd if=/dev/zero of=/dev/mmcblk0boot0

  • We set eMMC boot mode. Now as per technical reference manual board should not get booted because there nothing in boot partition of eMMC (USDHC1). But surprisingly it start booting from inserted SD card (USHDC2). Which is strange and incorrect!!!
  • If we flash eMMC boot partition --> set eMMC boot mode --> boot from eMMC it works fine. Which correct.
  • But there is one more interesting observation. If we SD boot mode -->remove SD card -->power on board.
  • As per Technical Reference Manual it should jump to USB serial mode and before that is should go to USDHC1 interface (eMMC)  and boot from there. But here nothing is happening.
  • Boot behavior is contradicting from description in Technical Reference Manual.

Has anyone observe such behavior? Is there in correction needed in Technical Reference Manual description?

Any suggestions or inputs are appreciated. As this is critical stage before we proceed ahead.

 

Thanks,

Jemish

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