[Libre-soc-dev] nmigen tutorials etc.
andrey at technepisteme.xyz
Thu Oct 14 12:51:43 BST 2021
On 10/10/2021 21:38, Luke Kenneth Casson Leighton wrote:
>>> actually you can still get many of them by using archive.org
>> Great idea! I'll check to see what I replaced and find the equivalent
>> archive.org links.
> i think i did that for lambdaconcept tutorials already, somewhere.
> http://libre-soc.org/resources/ ?
Searched web.archive.org, could not find these as they were not backed
up by the wayback machine:
It's probably not critical, as I did find similar equivalents.
>>> the alternatives - which i describe in detail here - are absolutely
>>> flat-out bat-s*** insane.
>> Gave it a read. Now I finally have an idea of what PartionedSignal is
>> meant to do. With a signal example it made much more sense.
> you see why it's completely bast-hit sinane to try to do a batch
> if elif-elif-elif-elif cases in the actual ALU?
> imagine you have 600 lines of ALU code (something really complex).
> now duplicate that 4 times.
> or, worse, try to do explicit gate-level optimisation, where in the
> ALU you explictly design-in the low-level SIMD "partitions" > actually right there, in the ALU.
> By using PartionedSignal in the ALU, aren't you going to get HDL with
those partitions built-in? Or is the plan to have a configuration
parameter for synthesising either normal, or SIMD-partitioned version?
>> Parallel bit groups that can be operated on separately, or combined
>> together if no partitions are enabled.
> yes. now it turns out (and it was Jacob who came up with this
> concept, first) that you can do tricks for e.g. "add" by having
> partition bits actually *in* the underlying add: a 64-bit add becomes
> a 64+7 bit add, and you use carry roll-over to get it to *look*
> like they're "real" partitions.
What do you need 7 bits for? I'm guessing you only need perhaps 3 bits
if you want 8 partitions, so are the others for carry?
>> Had a brief look at the code, nMigen did start pretty far down, most of
>> the start is data structure setup.
> ridiculous, isn't it? 99% of it is python. you actually have to look
> *really hard*
> to find actual nmigen AST.
> if this were a "normal" industry-standard project, the ISA decoder would
> have been written out explicitly "by hand", wouldn't it?
> in the actual "language" of the project, yeh?
> like this:
Ah yes, don't you like all of those repeated entries? Doing that by hand
(even with copy-paste) sounds like great fun...
> i went, "oo that looks like a CSV file, let's *make* it a CSV file and
> then it can be machine-read elsewhere"
Sounds like a sane thing to do. I think data re-organisation in general
seems to be difficult for a lot of disciplines, apart from software
engineers. For example, instead of seeing that ISA decoder as a table
that could be manipulated in whichever way, seeing it only as a VHDL
> i cannot count the number of Dilbert cartoons i've read on this theme...
> Comedy is the best way to pass along the truth eh?
> with the SIMD thing we'll reaaaallly have to do a walk-through of the
> resultant HDL because it risks expanding out of control.
Are we able to reuse the formal verification done at python level for
the synthesised SOC?
> i remember someone doing operator-overloads in c++ (pointers,
> casts), and wondering why their code wasn't running very fast,
> and a more senior engineer taking them through it in a debugger,
> single-stepping down the chain of overloads, dozens of levels...
> Ah, someone OOP'd too hard? Hahaha
>> abstract concepts have almost nothing to do with C, and with each
>> release they seem to pile up more and more.
> sigh. i loved c++ when it was Bjarne Strousup's 2nd Edition book.
A Tour of C++, Second Edition? I'll put that on my reading list.
> the templating libraries have gotten waaay out of hand since then.
>> Didn't the first C++
>> compilers take a really long time before they became viable?
> my first exposure to c++ was i think borland's compiler. 1992.
So much history in computing, so little time...
>> Do you mean add the mail archive link to the tutorial page?
> yes. usually we do a "links" section bullet-points at the top.
>> > and one about the reason why to use "show top"
>> And as for "show top" do you want an explanation ("block diagram is
>> useful for visualising the internal architecture and compare with
> if *you* think it would be helpful - to you - and to others - then yes.
Added. Realised only after watching your recent OpenPOWER course video
that you can select the hierarchy to view with "show".
More information about the Libre-soc-dev