iMX7S POR issue

[ashokrajasekar]

Hello,

We have a custom board with iMX7S processor and da9062 dialog PMIC for Power Management and POR of the iMX7S.
Also a USB OTG port which has board's input power, whose VBUS is connected as VSYS to da9062 PMIC which then powers-up iMX7S & peripherals.

The board is configured to boot with BOOT_MODE_CFG[1,0] = [00] = fusemode boot
As the eMMC is not programmed with u-boot bootloader, the board goes to USB serial downloader mode,
So we build the custom u-boot for the board and download & run using imx_usb application from host linux through USB OTG interface,
We are able to get the u-boot serial console boot messages and prompt successfully.
Then we programmed the u-boot at 1KB offset on 8GB eMMC chip
using u-boot "ums 0 mmc 0" command and from linux host "dd if=u-boot-dialog.imx bs=512 seek=2 of=/dev/sd<X>.
Also we programmed the iMX7S eFuses(bank 1, word 3) using u-boot fuse command & fuses read back as below.
If we do reset command from u-boot prompt loaded from imx_loader, we are able to boot u-boot from u-boot from eMMC.

=> fuse sense 0 0 4 
Sensing bank 0:

Word 0x00000000: a0030103 8c2400d3 00000314 00000000
=> fuse sense 1 0 4
Sensing bank 1:

Word 0x00000000: 20000040 50821001 00000000 10002820
=> fuse sense 2 0 4
Sensing bank 2:

Word 0x00000000: 00000000 00000000 00000000 00000000
=> fuse sense 3 0 4
Sensing bank 3:

Word 0x00000000: 00000000 00100000 00000000 000db600

*  But when we power off and on the board through USB otg power, once the POR reset is asserted, the board is not booting from -eMMC, but goes to serial loader mode.

But when we download u-boot using imx_loader and we do reset command from u-boot prompt, we are able to boot u-boot from eMMC.

*  When we measured the delay between VSYS(from USB_OTG_power) going to DA9062 stabilize TO nRESET from DA9062(POR_B- reset to iMX7S POR) deassert delay is sufficient by 35ms to boot u-boot bootloader from eMMC. But u-boot is not booting from eMMC.

Query:
From this we observed the issue with POR, Is 35ms delay between VSYS to POR is not sufficient?
Is there any other factor governing POR?

[Yuri]

Hello,

  Please verify power up sequence of i.MX7S, using its Datasheet.

In particular - section 4.1.8 (Power-up sequence).

https://www.nxp.com/docs/en/data-sheet/IMX7SCEC.pdf 

Have a great day,
Yuri

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