IMX8MN Flashing Fuses / Secure Boot

[heiko]

Hi ,

Im in the process of enabling secure boot (hab) on a customboard with an IMX8MN.
I followed the CST_UG.pdf and AN4581.pdf . With most of the steps im done, i got my signed images for spl and u-boot. 

Next step would be flashing my 4 generated SRK keys/hashes to the nano.
In the Application Node and here(which i found sadly really late) I learned that you can use u-boot to program the fuses. I was wondering if there isnt a way to program the fuses using uuu.
Some searches later I think there should be a way by using uuu with an "auxiliary"-binary and a scritp but i couldnt find much more then this bit of information. Is there a way to do it with uuu and is there some documentation for this available ?

thanks in advance

[Bio_TICFSL]

Hello,

Yes, you can program fuses using the Universal Update Utility (UUU) tool. This approach is particularly useful in manufacturing environments and can be more convenient than using U-Boot commands directly.

To program fuses with UUU, you need to:

1. Create a UUU script (typically named uuu.auto) that loads U-Boot and then executes the necessary fuse commands.

Here's an example script structure:
```
SDPS: boot -f imx-uboot.bin-flash
FB: ucmd fuse prog -y # Format for programming fuses
```

For programming SRK hash fuses specifically, you would use commands like:
```
FB: ucmd fuse prog -y 6 0 # Example for first word of SRK hash
FB: ucmd fuse prog -y 6 1 # Example for second word
FB: ucmd fuse prog -y 6 2 # Example for third word
FB: ucmd fuse prog -y 6 3 # Example for fourth word
```

When programming SRK hash fuses, first dump the values from your SRK_1_2_3_4_fuse.bin file using:
```
od -t x4 SRK_1_2_3_4_fuse.bin
```

Important recommendations:
1. Always verify HAB status after programming the SRK hash but before closing the device
2. Only close the device if HAB status is OK with no HAB events
3. Refer to the UUU documentation for complete command syntax: https://github.com/NXPmicro/mfgtools/releases/download/uuu_1.4.193/UUU.pdf

For additional information, check the i.MX8M secure boot guide at: https://source.codeaurora.org/external/imx/uboot-imx/tree/doc/imx/habv4/guides/mx8m_secure_boot.txt?...

Regards