MATLAB Answers

Generate Valid In, Valid Out with HDL Coder - Best practice?

10 views (last 30 days)
TS
TS on 20 Nov 2017
Commented: Ludo Visser on 7 Aug 2018
I am using Matlab HDL Coder to generate VHDL Code and want to add a "valid in/out" Port to my subsystems to ensure the timing in sequential operations on a macro level.
Valid in: Triggers the calculation of the subsystem with the current values of the subsytem input ports
Valid out: Signals (e.g. with an rising edge) that the calculation of the subsystem is finished
I have tinkered with several idears:
- Enabled subsystem with a state machine outside of the subsystem to control if the output values have changed
- A parallel path inside the subsystem which just routes the valid in directly to valid out - a rising edge is sourced when the calculation is started -> with "balenced delays" the valid out signal (should) rise when the calculation is ready
- some minor variations of the above / unsucessful approches
So , what is best practice when implementing a valid in / out control for a HDL Subsytem?

Answers (1)

Ludo Visser
Ludo Visser on 7 Aug 2018
I typically follow your second suggestion. I used enabled subsystems to split up the computations into blocks that can either be done in a single clock cycle (like addition, logic, etc.) or that require a predictable number of pipeline registers (e.g. multiplication). In this way, I can manage the results of the delay balancing feature (which I really dislike, but that's another discussion).
A typical subsystem looks like this:
You can see the "input valid" to "output valid" line in the top and the data line directly below it.
As you can see, I'm generous with unit delays, so I can predict better where the delay balancing will insert delays. In later stages, if I run into performance issues, I can optimize a bunch of them away, but typically it's not necessary in my applications.
  2 Comments
Ludo Visser
Ludo Visser on 7 Aug 2018
I also turn it off at the top level. It's annoying that HDLWA pushes this setting so hard - it generates an error if you turn it off, which you can only bypass by setting "ignore warnings", and who knows what other warnings go unseen because of that.

Sign in to comment.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!