eFuse Programming

[smarano]

Hi
I'm tring to program my cmod a7 35T Digilent board with an encrypted bitstream. I read that to do this i need to program the eFuse register with a key.nky file, but when i try to do this i found a problem. 
This board don't have a jtag connector but it can be programmed via usb. When i try to program efuse a found a problem "cannot program efuse register with this cable". 
Anyone can tell me if there is another way to program efuse or if this board can't support encryption bitstream?
regards Stefano

[jpeyron]

Hi @smarano,

I reached out to our design engineer and found that access to the VBAT pin on the Cmod A7  is impossible. There’s no way to attach a coin cell to just the VBAT pin because it’s hard tied to the VCC1V8 rail and the trace that connects the FPGA ball to the via that goes straight to the VCC1V8 polygon is underneath the FPGA. Therefore a cut and jump is not possible. We didn’t have space for an auxiliary JTAG connector on the CmodA7, which means that the JTAG signals aren’t routed out to a header. That will make attaching an external program very difficult, if not impossible.

thank you,

Jon

[JColvin]

Hello @smarano,

Those of us here at Digilent have not done eFUSE programming with our boards and we do not offer any support for it. Since you are receiving an error stating that you cannot program the efuse register with this cable, I suspect that the Cmod A7 35T is not able to support an encrypted bitstream.

I'm sorry I could not be of more help.

Thank you,
JColvin

[JColvin]

Hello @smarano,

One of my co-workers pointed out a thread where another user was using the Cmod A7 for eFUSE here: 

I apologize for the confusion.

Thank you,
JColvin

 

 

[smarano]

@JColvin Thanks.

 

I had already read the other discussion about the coin-battery but it's not clear about what kind of battery, how to connect the battery etc etc. I realy need something that can allow me to program the eFuse register. Are you sure that with this board i can't use eFuse to encypt my bitstream? If not there is another guide more detailed about the coin-battery solution?

[jpeyron]

Hi @smarano,

We have no experience using eFuse and would not have helpful input. Looking at the linked forum thread above it is possible to program the Cmod A7 with eFuse. Hopefully one of the more experience community members will have some input for you. I would also suggest to look at the Vivado Design Suite User Guide Programming and Debugging pdf.

thank you,

Jon

[smarano]

@jpeyron

in the linked forum thread above there is no valid information about efuse programming with cmod a7 and when i try to program it using vivado an error message is showed : "Cannot program efuse with this cable" 

I think that the problem is that the cmod a7 is missing of jtag connector and the jtag-usb chip isn't capable to do this. Now i'm searching for some information that confirm to me this supposition or not