topic Re: How to disable JTAG on i.MX 8M? in i.MX Processors

How to disable JTAG on i.MX 8M?

christian_mauderer — Mon, 09 Sep 2019 11:53:12 GMT

The i.MX 8M reference manual mentions a JTAG_SMODE[1:0] and a SJC DISABLE e-fuse that are necessary to disable JTAG access. But I can't find the address or location of the fuses. Where can I find them? Is there some document describing it?

Re: How to disable JTAG on i.MX 8M?

igorpadykov — Tue, 10 Sep 2019 00:28:02 GMT

Hi Christian

one can look at

Understanding how to burn eFuses on i.MX8 and i.MX8x families - i.MXDev Blog

https://community.nxp.com/thread/505184

Best regards
igor
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Re: How to disable JTAG on i.MX 8M?

christian_mauderer — Tue, 10 Sep 2019 05:22:09 GMT

Hello Igor,

thanks for the reply. My problem is not how to set a fuse in general. It's more the problem where this specific fuses are located.

For example: The reference manual tells me that BT_FUSE_SEL is at 0x470[28] and it tells me that this is bank 1 word 3. But it doesn't tell me a location for JTAG_SMODE[1:0] and SJC DISABLE. For i.MX6 or i.MX7 there is another document that tells me the location (https://www.nxp.com/docs/en/application-note/AN4581.pdf ). But I didn't find one for i.MX8.

Best regards

Christian

Re: How to disable JTAG on i.MX 8M?

igorpadykov — Tue, 10 Sep 2019 07:12:05 GMT

Hi Christian

I sent additional details by mail.

Best regards
igor

Re: How to disable JTAG on i.MX 8M?

christian_mauderer — Tue, 10 Sep 2019 07:19:12 GMT

Hello Igor,

thank you. That solved my question.

Best regards

Christian

Re: How to disable JTAG on i.MX 8M?

marcelziswiler — Sat, 16 Nov 2019 12:21:50 GMT

Thanks, igorpadykov, very helpful to answer this by mail!

How about others like us who are also wondering about all this?

Re: How to disable JTAG on i.MX 8M?

tgs — Wed, 02 Feb 2022 12:30:59 GMT

Hi Igor

Can you please send me the same information as well.

Thanks in advance,

Re: How to disable JTAG on i.MX 8M?

marcusfolkesson — Wed, 01 Jun 2022 06:33:02 GMT

Please post the solution here instead of sending it to one single recipient. There are too many threads here that end with "I sent you a mail". The thread is useless for everyone but the thread creator.

I would like to have this information as well.

Thanks,
Marcus

Re: How to disable JTAG on i.MX 8M?

M_J — Thu, 14 Jul 2022 08:18:50 GMT

Hi @igorpadykov

Could you forward to me details as well?

Kind regards,
Marcin

Re: How to disable JTAG on i.MX 8M?

bernhardfink — Mon, 12 Sep 2022 16:09:30 GMT

Meanwhile these fuse bits have been documented in the Security Reference Manuals of 8M Nano and 8M Plus. It's the same structure as in 8M and 8M Mini.

I will check

Why we haven't updated it for 8M Mini and 8M yet
Why it is not part of the OTP fuse description in the normal Reference Manual

Regards,
Bernhard.

Re: How to disable JTAG on i.MX 8M?

Nocker — Fri, 07 Oct 2022 05:06:12 GMT

Hi,

I have the exact same question, can someone let me know the answer please?

And I agree with what someone else has posted, it is not very useful when the answer results in a private email.

Regards,

Chris

Re: How to disable JTAG on i.MX 8M?

bernhardfink — Fri, 07 Oct 2022 06:16:51 GMT

Here is the description of these fuse bits:

Fuse Address	Fuse Name	Function	Setting
0x470[21]	SJC_DISABLE	Disable/Enable the Secure JTAG Controller module. This fuse is used to create highest JTAG security level, where JTAG is totally blocked.	0 - Secure JTAG Controller is enabled 1 - Secure JTAG Controller is disabled
0x470[23:22]	JTAG_SMODE[1:0]	JTAG Security Mode. Controls the security mode of the JTAG debug interface	00 - JTAG enable mode 01 - Secure JTAG mode 1x - No debug mode

Re: How to disable JTAG on i.MX 8M?

xuxa — Thu, 27 Jul 2023 01:58:10 GMT

Can you also send me the additional details?

Thank you.

Re: How to disable JTAG on i.MX 8M?

bernhardfink — Thu, 27 Jul 2023 07:56:53 GMT

I marked my answer from last year as solution, so that it's easier to find.

Re: How to disable JTAG on i.MX 8M?

Bhardwaj — Thu, 23 Oct 2025 09:38:53 GMT

Hi,

When we are read the bank 1 word 3 in I.MX8MPLUS after the U-BOOT ,we observe the below value.

Does it means ,Is JTAG is Disable?

You said that SJC_DISABLE and JTAG_SMODE are set high ,that means JTAG is Disable.

Does the I.MX8M fuse address are applicable for I.MX8MPLUS ?.

Fuse Address	Fuse Name	Function	Setting
0x470[21]	SJC_DISABLE	Disable/Enable the Secure JTAG Controller module. This fuse is used to create highest JTAG security level, where JTAG is totally blocked.	0 - Secure JTAG Controller is enabled 1 - Secure JTAG Controller is disabled
0x470[23:22]	JTAG_SMODE[1:0]	JTAG Security Mode. Controls the security mode of the JTAG debug interface	00 - JTAG enable mode 01 - Secure JTAG mode 1x - No debug mode

Re: How to disable JTAG on i.MX 8M?

bernhardfink — Thu, 23 Oct 2025 10:09:56 GMT

You seem to have a closed part. All 3 relevant bits are set. Bit definitions and the location are valid for i.MX 8M Plus.

Make a crosscheck with a debugger, if you don't see any core appearing, then the JTAG is definitely closed.

Regards,
Bernhard.

Re: How to disable JTAG on i.MX 8M?

Bhardwaj — Thu, 23 Oct 2025 10:36:06 GMT

1.How to enable JTAG Mode in I.MX8MPLUS ?

2.Is there any possibility to override that register in I.MX8MPLUS ? for I.MX6 a bit is mentioned to override JTAG_SMODE by setting the BOOT_CFG_LOCK bits as shown below?.

Re: How to disable JTAG on i.MX 8M?

bernhardfink — Thu, 23 Oct 2025 11:01:30 GMT

Closed is closed. If there would a way to re-open it, the closed configuration wouldn't make sense. The OTP bits are really just one-time-programmable.

The alternative way to access the chip is the Serial Download Protocol (SDP) on the USB port.

According to your readout, bit[28] = BT_FUSE_SEL is not set, so the device can still boot taking a configuration from external BOOT_MODE pins.

Regards,
Bernhard.

Re: How to disable JTAG on i.MX 8M?

kirankumar007 — Mon, 27 Oct 2025 08:36:14 GMT

Problem-1

1)We have I.MX8MP EVK has default image, stopped at u-boot using putty and checked below register JTAG

From above image JTAG Disable permanently one of of the NXP Support aslo given message.please confirm

Problem-2

1)We have custom board(i.MX8MP) doesnt have default image, any procedure for JTAG Access. Is it possible any where without default image JTAG access is possible????

2)If possible means how decribe procedure

3)if not, USB connections out cutstom device shown below

Its USB2.0 in EVK Type C connections given, said USB2.0 also compatible,then please given a procedure with our hardwrae and software loading using USB2.0.

Many days happen request you give clear and stright procedure for all of above

Re: How to disable JTAG on i.MX 8M?

kirankumar007 — Mon, 27 Oct 2025 08:39:06 GMT

Previous Post Image is not clear please check below