export as hierarchy (verilog modules)

[jordens]

I'd like to be able to translate the migen Module hierarchy into the exported HDL hierarchy at least to some extent.

• This would allow estimating resource usage at some useful granularity.
• It would allow easier exporting and re-use of migen gateware in verilog/vhdl projects.
• This would help with floor planning if one wants to do that.
• Vivado at least seems to have some options that allow some synthesis to be hierarchy-constrained and therefore potentially scaling better.
• I don't expect this to be able to map any of the metaprogramming and parametrization in migen to parametrization in verilog. That won't work. I am fine with exporting module parametrizations as separate and fully specialized modules.

Implementation idea:

• Module would receive a list of ios
• There would need to be some way to check/enforce/verify the interface, i.e. ensure that module inputs are not also assigned to from within a module and that internal Signals within a module are not accessed from the outside.
• Some way to substitute a Module by an Instance.
• build() would export specialized modules.

[whitequark]

i.e. ensure that module inputs are not also assigned to from within a module and that internal Signals within a module are not accessed from the outside.

Right now I see the fact that I can manipulate signals without regard to module boundaries as a major feature of Migen (and I believe it's used in ARTIQ quite a bit, too). Do you suggest blanket prohibiting this, or just when exporting? In any case, splitting the Migen language into two like that seems troublesome...

[jordens]

No. This shouldn't touch existing code style or features at all. It's just an trade-off that one has to accept and deal with when exporting hierarchy. This will only give you the tools to do so.

[mithro]

@jordens Are you actively working on this at the moment or is this something you would just like to see in the future?

[jordens]

I would like to see it and don't have substantial progress.

[phire]

I think this can/should be done without requiring the user to specify a list of ios.

Just automatically infer them from how the module is used.

[whitequark]

Triage: fixed in nMigen.