topic Re: i.MX91 fusemap spreadsheet needed to write MAC addresses into OTP in i.MX Processors

i.MX91 fusemap spreadsheet needed to write MAC addresses into OTP

6502_z80 — Tue, 12 Aug 2025 08:02:06 GMT

Hello,

I have the i.MX91 FRDM devkit and would like to write the MAC addresses in the OTP.

Uboot can read (and probably write) the efuses (e.g: fuse read 0 1 returns 26d8).

Now I'd like to write the MAC addresses, but I don't know which fuse to write.

The RM says:

But I could not find the spreadsheet on:

https://www.nxp.com/products/i.MX91

Where can I get the spreadsheet?

Also, which fuses are used to store the MAC addresses?

Best regards,

Re: i.MX91 fusemap spreadsheet needed to write MAC addresses into OTP

Harvey021 — Wed, 13 Aug 2025 02:45:05 GMT

Hello @6502_z80

You can get the spreadsheet from the attachment of i.MX91RM as below.

And which fuse you need for the MAC from the Fusemap.

Regards

Harvey

Re: i.MX91 fusemap spreadsheet needed to write MAC addresses into OTP

6502_z80 — Thu, 14 Aug 2025 08:00:43 GMT

Hi Harvey,

the i.MX91RM is just a PDF document:

All 22 documents for the i.MX91 that are shown are PDF documents.

I need to know which fuses should hold the MAC addresses for the two Ethernet ports.

Best regards,

Re: i.MX91 fusemap spreadsheet needed to write MAC addresses into OTP

Harvey021 — Fri, 15 Aug 2025 04:14:08 GMT

Hi @6502_z80

You need to download the PDF - i.MX91RM that you highlight it, and then you will find attachment (as previous post) from the left panel after opening the PDF. You will find the below from the MAC fuse information.

The attached Fusemap for your reference.

Regards

Harvey

Re: i.MX91 fusemap spreadsheet needed to write MAC addresses into OTP

6502_z80 — Fri, 15 Aug 2025 06:48:54 GMT

Hi Harvey,

thanks for pointing out that the spreadsheet is inside the PDF. I was not aware that was an option.

FYI evince handles this well:

According to this document, the MAC addresses are stored in bank 39, words 315-317:

39, 315 MAC1_ADDR_31_0[31:0]

39, 316 MAC1_ADDR_47_32[47:32] and MAC2_ADDR_15_0[15:0]

39, 317 MAC2_ADDR_47_16[47:16]

When I try to access them in u-boot, I get an error:

u-boot=> fuse read 39 315
Reading bank 39:

Word 0x0000013b:ERROR

Programming them doesn't work:

u-boot=> fuse prog 39 315 0xA6B41D7F
Programming bank 39 word 0x0000013b to 0xa6b41d7f...
Warning: Programming fuses is an irreversible operation!
This may brick your system.
Use this command only if you are sure of what you are doing!

Really perform this fuse programming? <y/N>
y
ERROR
u-boot=>

This is u-boot 2024.04 (U-Boot 2024.04 (Aug 11 2025 - 12:04:12 +0200))

I have the same result when I try this using the u-boot that came with the dev kit in eMMC (U-Boot 2024.04+gde16f4f1722+p0 (Sep 02 2024 - 10:44:35 +0000))

Writing them from user space is not an option anymore (we used to do this on i.MX6ULL), so u-boot is the right choice, correct?

Am I missing an u-boot patch? Do I need to "unlock" something first?

Best regards,

Re: i.MX91 fusemap spreadsheet needed to write MAC addresses into OTP

Harvey021 — Fri, 15 Aug 2025 09:24:21 GMT

Hi @6502_z80

The word that you use is not correct. Send you a demo for reference.

Regards

Harvey

Re: i.MX91 fusemap spreadsheet needed to write MAC addresses into OTP

6502_z80 — Fri, 15 Aug 2025 12:37:46 GMT

Hi Harvey,

thanks for your explanation how the banks/words are addressed.

I successfully programmed my two MAC addresses into OTP using uboot.

To program MAC 665544332211 and FFEEDDCBBAA write:

44332211 to bank 39 word 3
BBAA6655 to bank 39 word 4
FFEEDDCC to bank 39 word 5

Thanks!