Available flip flops

General discussion about the Mojo
Post Reply
tomisek
Posts: 6
Joined: August 19th, 2014, 1:22 am

Available flip flops

Post by tomisek » May 19th, 2017, 1:04 am

Hello,
I have a weird problem. I am developing my project in Xilinx ISE(14.7) so I can watch how many flip flops was used. As soon as the "Number with an unused Flip Flop" decrease under 50% FPGA becomes unstable. I can still load the bin file (Mojo Loader 1.3.0) and Mojo still works somehow but it is not reliable. There are no errors, no warnings, I meet all timing constraints. I tried it out many times and the result was everytime the same. As soon as I add some part of code which increase number of used FlipFlops it becomes unstable although there is no connection between added code and functionality(stability) of Mojo.
Unfortunately I can't say what is the origin of unstability. It's somewhere in evaluating input pins but I don't know where :-/.

I tried to solve the same problem with Justin two years ago, when I was convinced the problem is in size of the bin file. I sent him the bin file, we discussed it a lot but we didn't find any reason why it happened. Now I noticed the connection between stability and "Number with an unused Flip Flop" so I hope there is some explanation.

Thanks, Tom

tomisek
Posts: 6
Joined: August 19th, 2014, 1:22 am

Re: Available flip flops

Post by tomisek » May 19th, 2017, 6:05 am

I did further research and tests and I found out that stability isn't dependent on unused FlipFlops :-/. Now, I have no clue what the probem could be. It looks like I have reached any top level of hardware sources of FPGA. Although Xilinx ISE doesn't indicate any problem or warning.I can add to my code whatever and wherever and it becomes unstable. Has anybody experienced anything like this yet?

thanks, Tom

embmicro
Site Admin
Posts: 834
Joined: March 24th, 2013, 12:45 pm

Re: Available flip flops

Post by embmicro » May 31st, 2017, 5:32 pm

I'd be willing to bet that the issue happens because the tools route your design a little differently which exposes some unrelated underlying problem.

Can you post your project?

Daisy221
Posts: 1
Joined: October 23rd, 2017, 4:18 am

Re: Available flip flops

Post by Daisy221 » October 23rd, 2017, 4:20 am

a flip-flop or latch is a circuit that has two stable states and can be used to store state information. A flip-flop is a bistable multivibrator. anything else ?

Post Reply