[IMX8ULP] M33 firmware boot partitions

[sert1m]

Hello! 

We are using IMX8ULP with M33 in singleboot mode. We have figured out that there are two partitions where M33 firmware can be stored: /dev/mmcblk0boot0 and /dev/mmcblk0boot1. M33 can boot from either boot0 or boot1 partitions. It seems like if firmware is not found at boot0 it uses firmware from boot1. 
Is there any way to control what partition (boot0 or boot1) should be used for boot? How does ROM select what partition to use for M33? What is recomended way to safely upgrade M33 firmware and ensure that we always have one working partition?

[AldoG]

Hello,

In this scenario, A35 ROM is the one that loads M33 FW, so in a normal boot flow the sequence of boot stage moving is Primary image set boot => Secondary Image Set boot => Recovery boot => USB serial download boot;

Here is where Secondary image set comes to play, please refer to reference manual chapter 12.1.5.2 Typical boot image layout.

Best regards/Saludos,
Aldo.