[vhdl-200x] Hetereogenous interfaces

(Originally sent just after the last telecon, but my email address has changed since I signed up to the reflector, hence a slight delay. Thanks to Jim for working through this with me!)

Hi all,

Thanks Jim for making the meeting recording available - that will enable me to keep up with the discussions as well as just reading the Wiki pages - hopefully I can make some constructive comments again :)

With regard to the duplication of elements when creating a port view (for defining visibility): Although it does seem verbose, it also feels (to me) very VHDL-like.  The verboseness is not as big an issue as it might seem (to my mind) as it is only a "one-off" piece of code when defining an interface for use, so the "end-user" of an interface will only have to "make use" of these definitions.  For example, I recently did a system full of AXI and AXI-Stream interfaces - I would only have needed each of those interfaces creating in a package once at the start of the project, and then I could have gained enormous amounts of readability and code-size reduction, even if those packages were a bit big.  And with standard buses like that, I probably wouldn't have even had to write them myself :)

A more critical issue (it seems to me) is that the user of the interface (in an entity) gets verboseness in the use of many dotted-relationships (and the use of aliases to make it more tractable)..

Looking at the example of the "slave_ent" from Ernst's proposal would it also be possible to do this:

---
alias mst is cpu_bus_rif.master_rl;
alias slv is cpu_bus_rif.slave_rl;
---
and then refer to "mst.addr_vl", "slv.data_vl"?

This might be a useful halfway-house?


Another thought which occurs to me looking at that example: the passing of the slave ID to the slave "feels wrong" - the mapping/wiring to specific slaves should be done in the higher-level instance. The slave should be unaware of its "location" in the system.  But maybe that's a point of opinion rather than technical!

(also, reviewing http://www.eda-twiki.org/cgi-bin/view.cgi/P1076/HeterogeneousInterfacesWithReuse I notice the code examples have become full * chars around reserved words...)

Cheers,
Martin


--
Martin Thompson BEng(Hons) MIET CEng
Technical Specialist - embedded systems

Conekt
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martin.j.thompson@zf.com<mailto:martin.j.thompson@trw.com>

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