Implement ConvertProtocol typeclass

[lmbollen]

I've ran into the situation where I have to implement components that boil down to converting between different memorymapped protocols that will be named protocolAToProtocolB and I wonder if we can implement this with typeclass (or other abstraction) instead.

i.e. I'd like to have maybe:

-- | Convert a protocol to another protocol within the same clock domain
class (Protocol a, Protocol b) => ConvertProtocol a b where
  convertProtocol :: Clock dom -> Reset dom -> Enable dom -> Circuit a b

Where we can make instances like for example:

instance (KnownAxi4StreamConfig conf, DataWidth conf ~ width) =>
  ConvertProtocol (PacketStream dom width user) (Axi4Stream dom conf user) where
  convertProtocol clk rst ena = undefined

You have to have some restricting laws for such a typeclass otherwise it could do anything. For example that the data produced by a can be recovered from b.

I've also noticed that probably the application space is rather limited due to many protocols not adhering to the same format. Because there are protocols for different applications(Streaming vs memory mapped) or the fact that Axi4 stream is defined using multiple protocols / channels.

I'm curious to hear if other people have thoughts on this.

[christiaanb]

Having explicit conversion functions, e.g. avalonMMtoAxi4Lite has the following pros:

• searching for the protocol will give you these conversion function
• the name indicates exactly what protocol conversion is happening at the point where it is applied (better “self-documentation”).
• You can have additional parameters for certain conversions; i.e. a fifo depth for a axi4 to axistream conversion

Cons:

• more names to learn and remember
• n! conversion function names for n protocols (though there aren’t that many compatible ones?)
• LLMs: have to wait for the next training cycle for new conversion functions to be learned/picked up

[martijnbastiaan]

My feeling is that this one is major:

You can have additional parameters for certain conversions; i.e. a fifo depth for a axi4 to axistream conversion

IMO we should just build 10 converters and then see if a type class is worth it.