[libre-riscv-dev] [Bug 325] create POWER9 TRAP pipeline

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=325

--- Comment #18 from Cole Poirier <colepoirier at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #15)
> https://git.libre-soc.org/?p=soc.git;a=commitdiff;
> h=2955619bc39a83b09920f8452882c4c327d30fef
> 
> cole, this is important to understand: you *do not* need to "understand"
> what is "going on".  you do not need to read 1,300 page PDFs - in full -
> memorised in their entirety - before being able to take action.
> 
> this can be extremely uncomfortable.  it feels... "unnatural", like,
> "i should know everything because if i don't i might make a mistake or
> implement the wrong thing".
> 
> sound familiar?
> 
> please understand: "understanding" != "action".
> 
> the trick that i learned - a long time ago, from doing reverse-engineering -
> is to find someone else's *working* implementation, and *without*
> understanding,
> perform as direct a one-to-one translation as is humanly and conveniently
> possible.
> 
> forget optimisation.
> 
> forget "understanding".
> 
> forget even *bug* fixes.
> 
> just... get... it... translated.
> 
> through that process, it turns out that by walking over the code (which you
> quotes don't understand quotes), this puts that code into your brain.
> 
> **THEN** when you read the spec - the 1300 page PDF - you go, "ohhhh,
> yeahhh, i
> recognise that.  that's those bits/flags/functions/insert-whatever that i saw
> when i was reading and translating the code, line-by-line".
> 
> and *NOW* you have quotes understanding quotes.
> 
> without having taken that first step, i guarantee to you that you will get
> nowhere, fast.
> 
> 
> so just - and i mean this literally - translate the comments that i've put
> from microwatt execute1.vhdl into nmigen.  you can see how Michael and i
> did that already for both OP_TRAP and OP_MFMSR.
> 
> i deliberately inserted the original microwatt code even for those, so that
> you have a direct side-by-side comparison, and can follow the adage
> "A is to B, as C is to D".
> 
> you'll also need to translate the bit-patterns MSR_* - this again should be
> obvious and easy.

With you all the way Luke, just needed this redirection/confidence boost.

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