Boundary Scan on IMX7

[pivkluka]

Hi All,

We are trying to do a boundary scan on IMX7D and IMX7S. As far as we can tell there are 2 modes for JTAG. 

Debug and Test mode. Our hardware is designed to pull JTAG_MOD pin always down so we go to Debug mode. 

Now if I pull that resistor up I can enter the boundary scan and do my tests. 

Issue is that pin JTAG_MOD is pulled down and as far as we can tell from reference manual we have to go trough DAP to be able to do boundary scan.

My 1st question is -> Is it even possible to do boundary scan this way? Or do we need to be in test mode to do it? 

If its possible do you have some hints on how to configure DAP to be able to do boundary scan. I do not want to rewrite all the software I currently have to do boundary scan so it would be nice if there is an easy way to do it while JTAG_MOD is pulled down.

Thanks.

Luka

[bernhardfink]

Hi Luka,

there is no software setting which lets you bypass the DAPs included in the chain with JTAG_MOD = 0.

In principle you could shift things through all the attached blocks, but when it comes to boundary scan mode you need to put the cores into reset state (for example with the EXTEST instruction). And at this point the chain becomes invalid.

To perform boundary scan, you need to have an activity from the outside which pulls the JTAG_MOD high. You mustn't change the pull-down resistor of course, you only need to apply a stronger level in high direction to the JTAG_MOD pin.

Regards,

Bernhard.

[pivkluka]

So just to be clear, there is no other way to do boundary scan than pulling MOD to 1?

Also is this picture true for IMX7? It say Cortex A9 on one core? I think this is taken from IMX6 not IMX7? 

[Yuri]

Hello,

  You may look at section 4.11.1.4 (JTAG topology) of i.MX7D RM.

http://www.nxp.com/assets/documents/data/en/reference-manuals/IMX7DRM.pdf  

As for Boundary Scan, usually BSDL file contains attribute COMPLIANCE_PATTERNS,
where JTAG_MOD is stated  as pulled up. 

Regards,

Yuri.