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From: Lawrence Stewart <>
To: Douglas McIlroy <>
Cc: TUHS main list <>
Subject: Re: [TUHS] Encoding an ISA: Random Logic vs. Control Stores
Date: Wed, 1 Dec 2021 16:14:02 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

> On 2021, Dec 1, at 9:55 AM, Douglas McIlroy <> wrote:
> My take on defining random logic
> random logic : hardware :: spaghetti code : software
> Doug

I don’t think this is right.  The irregular parts of die photographs didn’t get that way because the hardware engineers were writing bad (spaghetti) code.  They got that way due to several levels of optimizing tools working over quite sensible RTL or System C code or whatever. You might as well ding the output of -O3 for being incomprehensible.

You might get the same logic by writing a clean state machine and letting the tools minimize the control rom into gates (good) or by writing the gates yourself (bad).  You can’t tell without looking at the sources.

Software coding:  You write the conrol flow and the compiler generates the datapath
Hardware coding:  You write the datapath and the compiler does the control logic.

  parent reply	other threads:[~2021-12-01 21:23 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-01 14:55 Douglas McIlroy
2021-12-01 20:27 ` Jon Steinhart
2021-12-01 21:14 ` Lawrence Stewart [this message]
2021-12-01 22:09   ` Jon Steinhart
  -- strict thread matches above, loose matches on Subject: below --
2021-12-01 13:59 Paul Ruizendaal
2021-11-30  8:07 pbirkel
2021-11-30 15:19 ` Ron Natalie
2021-11-30 15:30   ` arnold
2021-11-30 15:39     ` Ralph Corderoy
2021-11-30 18:50     ` Jon Steinhart
2021-11-30 21:45       ` Humm
2021-11-30 23:07         ` Jon Steinhart
2021-11-30 23:18           ` Henry Bent
2021-12-01  5:00             ` Jon Steinhart
2021-12-01  6:27               ` pbirkel
2021-12-01 16:42                 ` ron minnich
2021-12-01 17:08                   ` Ron Natalie

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