DIR_BT_DIS and others

[antonio_santagi]

Hello,

at https://source.codeaurora.org/external/imx/uboot-imx/tree/doc/imx/habv4/guides/mx8m_mx8mm_secure_boo... 

I read about DIR_BT_DIS register field and how to write it with fuse prog command. Checked also on the AN4581.pdf guide.

However in the iMX8M Mini reference user manual I can't find its description and location on the fuse map.

I can find it on the shadow register but they say look at the fusemap for the description, and there I can't find any reference to it.

the bit set to 1 by the fuse prog command is bit 27 and bit 27 is stated as 'reserved' in the fuse map.

Same problem also with the register SJC_DISABLE ( this is not even mentioned in the shadow register bank 1 word 3 description )  .

am I missing something or is the manual missing these registers in the fuse map description ?

thank you

[frix]

Good day,

Thank you for the register definitions. This helps a lot.

Do you perhaps have the register address & bit position for the JTAG_HEO and KTE fields?

JTAG_HEO

Addressed in paragraph 4.11.5.2: Software Enabled JTAG, it states that "By writing '1' to HAB_JDE (HAB JTAG
DEBUG ENABLE) bit in the e-fuse controller module, the JTAG is opened, regardless of its security mode"

Further in the paragraph it says: "JTAG_HEO e-fuse disables this feature"

KTE: Kill trace enable

Defined in the reference manual in paragraph 4.11.5.3: Kill Trace. 

"The kill trace feature needs to be activated by burning a dedicated e-fuse. If the fuse is left intact, kill trace is never activated"

From this it seems that we need to program the fuse to enable the 'kill trace' signal

Regards,

Frikkie

[antonio_santagi]

thank you, that is useful to know.

[IvanRuiz · Accepted solution]

Hello,

Firstly, a new revision of the i.MX8MM RM has just dropped on the external web page. 

DIR_BT_DIS has been removed since it is a reserved bit in this device and will always come programmed from the factory. The application note that mentions is generic; not everything it mentions applies to all i.MX devices. 

The fuse SJC_DISABLE and JTAG_SMODE are missing from this latest RM as well. We have reported them to get these fixed in the next revision of the RM.

The relevant info for those fuses is:

Fuse addr	Fuse name	Num bits	Fuse function	Setting	Used by
0x470[21]	SJC_DISABLE	1	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	SJC
0x470[23:22]	JTAG_SMODE[1:0]	2	JTAG Security Mode. Controls the security mode of the JTAG debug interface	00 - JTAG enable mode 01 - Secure JTAG mode 11 - No debug mode	SJC

Hope it helps!

BR,

Ivan.