JTAG CAPABILITY WITH DIGILENT DISCOVERY

[JAlaj]

Hello Team,

After a successful implementation of SWD, i am now looking to communicate via JTAG protocol using Digilent Discovery.

Please route me to any available example for same

Thanks,

Jalaj

[Shalin]

Hi @attila

 

We are trying to use Digilent digital discovery for JTAG read and write. Currently, in the waveforms tool, there is no option available to write/read, execute the script. I am also attaching a screenshot below for your reference. 

Thanks,

Shalin

[JColvin]

Hi @Shalin and @JAlaj,

As you noted the transmitting portion of JTAG is not implemented.

I suspect the reason for this is because the amount of different headers and scan types is too involved to make this a feasible effort of Attila's time. I do not know nor dictate what Attila's schedule is, so this is speculation on my part.

Thanks,
JColvin

[attila]

Hi @JAlaj @Shalin

You could use the SPI functions for JTAG operations, just make sure the last shifted bit is transferred with TMS high.
Another option would be using dedicated JTAG cables/modules:
https://digilent.com/shop/boards-and-components/programmers/jtag-cables/
https://digilent.com/shop/boards-and-components/programmers/jtag-modules/

[JAlaj]

Thanks Attila

We do not have a slave device at present which can understand JTAG command and respond accordingly.

The idea is to use Digilent discovery HW to act as JTAG master to send command and decode the response.

As you mentioned to use SPI, and  last shifted bit with TMS high. Just curious, how the response on JTAG will be decoded.

Do you have any example, just for reference purpose. It will help to understand the command/response.

[JColvin]

Hi @JAlaj,

Digilent does not have any examples of running JTAG over SPI, no. The best source of the JTAG standard would be the IEEE 1149.1 or the IEEE 1149.7 documentation, both of which are available for purchase from the IEEE organization.

Otherwise, I would be looking for some sites that talk a bit about the architecture overview such as these two sites I found: https://vlsitutorials.com/jtag-architecture-overview/ and https://www.xjtag.com/about-jtag/jtag-a-technical-overview/. It also looks like Altera / Intel has a bit of information in their Application Note that is available on this page here: https://www.intel.com/content/www/us/en/docs/programmable/683705/20-3/jtag-protocol.html.

Thanks,
JColvin