🚀 go-pugleaf

On Fri, 30 Oct 2009 19:12:17 -0700 (PDT), MooseFET
<kensmith@rahul.net> wrote:

>On Oct 30, 2:09�pm, Jon Kirwan <j...@infinitefactors.org> wrote:
>[.. was PIC now 8051s ..]
>>
>> I'm using one from SiLabs, right now.
>
>Just one?  One of my designs is about to go into production with two
>F120s clocked at nearly 90MHz.  One of them is just about fully busy.  The
>other has many microseconds to spare.

I'm clocked at 24MHz.  Which is fine enough.  I think it's about 422
SYSCLKs.  At 90MHz, that would be more like 4.5 microseconds.  But I'm
not there.

>> in perfect shape.) �For this app, I needed a much faster floating
>> point ln(x) function (achieved under 18 microseconds) and found myself
>> spending some time coding assembly on it.
>
>Do you really need true floating point?  do you really need ln() or
>would log2() do?  18 microseconds seems a little slow.

It's running on 24MHz, not 90MHz, for one thing.  And it needs 20
precision bits in the result with an input value possessing a good 30
bits (the compiled result of thousands of other measurements.)

>Doing log2() of a 32 bit floater can be fairly quick if you don't
>care much about how much code space you use.

Well, I'm good already.  Plus, it is custom-tailored to the job.

>> �No question in my mind that
>> this processor was designed with hand-coded assembly in mind, though.
>> Very easy to use efficiently for a human coder, though I do have to
>> check the book often to see if a particular instruction supports a
>> particular mode of access, yet just the kind of thing to seriously
>> complicate a compiler's life.
>
>Real men code in assembly anyway.

I think better programmers are well experienced in using assembly and
will use it as appropriate, taking into account the tasks and clients.
Lacking such experience is the loss of a significant mental and
practical toolset that could otherwise be brought to bear on problems.
That doesn't mean every application gets coded entirely in assembly.

Jon


>> >But I found the varients of 8051 I used were obsolete on more than one
>> >occassion causing problems. I'm still sourcing SAB80C517 at silly
>> >prices for example.
>>
>> I gather that Atmel has an AT89 line that includes an external bus and
>> so does SiLabs. �Not sure how either of these would score on not
>> obsoleting designs, though.
>>
>> >I first used the PIC for very low cost apps around 1990 and found that
>> >there was always an upgrade path which didn't obsolete my designs.
>>
>> Yes. �I've been using PICs since the late 1980's.. just around the
>> very month that Parallax entered the public fray. �Nobody likes the
>> bare-bones ALU design for the smaller-width instruction families --
>> it's design guts lay out on the floor, plain to see. �But Microchip
>> has maintained a very serious commitment to upgrade pathways over the
>> entire time I've been involved (just after they decided to move beyond
>> the "million unit rice cooker customer" days and place them into a
>> broader marketplace. �I couldn't have guessed then how strong that
>> commitment would be. �But they seem to well know what is important and
>> they have clearly (to me) worked very hard to _earn_ the respect they
>> have gained. �And it's been so on almost every good business front.
>>
>> One begins to realize after experiencing such a company's commitment
>> to their customers, if that realization isn't already at hand, just
>> how relatively unimportant an instruction set is to all these other
>> business factors.
>>
>> >Secondly Microchip always have product available. �I recall one rep
>> >trying to convert me to the ST6. Then he said ST are behind on
>> >production and delivery was 4-6 months.
>>
>> Well, Microchip has had their days with delays (the wait for the
>> 18F252 from using the 18C252 comes to mind) but they have tended to be
>> shorter than longer delays.
>>
>> >There are better micros than the PIC from an engineering perspective
>> >but they are hard to beat from a production view point.
>>
>> In all the time I've used them, they have consistently maintained a
>> solid professional use pathway that simply doesn't break. �I have old
>> tools that they no longer make (ProMate II) and yet they still support
>> it without question or quibble. �If I have so much as a flaky power
>> switch they want me to send it in and fire off a replacement with
>> shipping included for the "bad" one, so that I don't even miss a
>> single second of use. �Same for the modules that plug into it. �Their
>> tools are supported, decades it seems after they don't sell them
>> anymore. �That takes commitment on their part.
>>
>> I find wringing of hands over the instruction set to be relatively
>> badly placed. �There are a lot more important things to focus on and
>> on those areas Microchip has done a yeoman's service across the board.
>>
>> Obviously, I use other manufacturers too. �It's _very_ hard to find a
>> 1MHz 16-bit SAR ADC anywhere in Microchip's monolithic cpu fold, for
>> example. �But none of have compared quite as well on the business
>> issues over the years.
>>
>> Jon