[libre-riscv-dev] DDR PHY

Cole Poirier colepoirier at gmail.com
Mon Feb 24 16:09:46 GMT 2020

> On Feb 24, 2020, at 7:46 AM, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
> EUR 600,000, not EUR 60,000.

Oh wow that’s really something! Quite close to the budget of a single NLNET grant. What I lovely mistake to have made, now the price seems 10x lower to me than I initially mistakenly thought.

>> I still am struggling to comprehend what PHY “is”,
> look it up.  PHY.  physical.  physical interface.

I try not to write anything to the mailing lists that I haven’t tried to research on my own before hand. I understand that this is a technical mailing list and such behaviour would be unproductive. The reason I was asking here is that I have looked it up and tried to research this dozens of times over the past 6 months and still not been able to understand what differentiates PHY from cores.

>> I’ve done a lot of googling and I’m still having trouble with this concept, can you point me in the right direction or to a resource that might help me understand better?
> honestly i can't. i simply picked it up by inference after noticing
> the context in which the word was used, a lot.
> "judgement" of "what is not understood or known right now" is a key
> mistake made by a lot of people.  "i don't understand EVERYTHING -
> every single absolute last tiny detail - therefore i'm going to freeze
> and lock up solid and fail to progress any further".
> don't understand?  pause... record the fact...  record the context
> (mentally) of the use of the word which is not understood.... note its
> use later.... collate MORE instances of where the word is used....
> cross-associate them.... notice the DIFFERENCES when the word is
> used....
> ... and over time, the end result is: understanding through context
> results in a natural inference of the word, without anyone or anything
> actually ever telling you what it "means".
> l.

I actually have not been making judgments and then freezing but have been using the method you describe. I’m quite comfortable with my utter lack of understanding about much of what get discussed on the mailing lists, I’ve read them regardless, and my understanding has grown through filling in things implicitly over time. If I had tried to understand EVERYTHING from the start, I wouldn’t be here now.

With this subject I understood that it literally meant PHYsical layer, but I was unable to progress any further in my understanding than that... until today :) In a nice coincidence, you have actually provided the exact hint I needed on the other LPDDR3/4 mailing list thread. The key understanding I was missing is the difference between digital and *analogue* design. It wasn’t that I was stuck, it’s that this was an unknown I’ve kept returning to without being able to progress in my understanding. With my new understanding that analogue design and synthesis is in an entirely different electrical engineering domain and cannot by synthesized from higher level languages like Verilog, I now have a vastly improved understanding of the nature of the distinct domains and their differing design, developments, and synthesis processes. So thank you for the fortuitous tip Luke! :)

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