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] =  = 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.
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?