[time-nuts] Generating a solid PPS from 10Mhz source

Bob Camp kb8tq at n1k.org
Sun Jan 17 09:43:41 EST 2016

> On Jan 16, 2016, at 7:40 PM, jimlux <jimlux at earthlink.net> wrote:
> On 1/16/16 10:07 AM, Poul-Henning Kamp wrote:
>> --------
>> In message <20160116080037.13903406057 at ip-64-139-1-69.sjc.megapath.net>, Hal Murray writes:
>>> kb8tq at n1k.org said:
>>>> The astonishing part of this “new world” is that a very complex chip that is
>>>> made in high volume is cheaper than a handful of less popular (but far less
>>>> complex) chips.
>>> It would be interesting to see the die sizes.
>> Die size is not really an issue until they become big enough to impact overall yield.
>> And apropos:  I just used a LPC810, to do 5MHz to 1Hz for my HP5065A clock.  It almost
>> feels surreal to use a 32bit ARM CPU, even in a DIP8, for something so mundane...
> And how many thousand lines of code (including libraries, etc. that may have been pulled in)?
> I had just this discussion yesterday at work with someone.   These days, silicon (even going into space) is much cheaper than people. Sure, you could optimize a hand crafted little routine in assembler. Or, you could just load up RTEMS, compile your program, link in newlib, etc., and have it working in a day.  If you've got 2 MByte of memory, nobody cares whether you use 1kbyte or 50kbyte.

These days, that code (thanks very much to a number of people and various market forces) is likely all *free*. Not just free as in I can “borrow” it from work. Free as in fully licensed for use at no cost. Not only is the code in that category, so is the IDE and all the programming and verification code that goes along with it. If you want to check it all out, the silicon guys (just about all of them) will give you a free (as in there is an obligation) board for your commercial project. They will sell you the same board for < $20 (not quite free) for your basement one-off project. Would I use those tools to send a gizmo to Pluto? Maybe not without some adult supervision. Are they used every day to do a wide range of things - yes indeed they are. 

Another un-mentioned issue (so far) is that my board full of logic can easily have an un-noticed bug in it. The same is true of my code. Either way, two years down the line there is a need to do something about it. In the case of the board full of logic, it’s get out the soldering iron time (and possibly ship parts back and forth time). In the case of the code based gizmo, out goes a patch. No hardware is swapped out. No soldering irons are involved. Yes, a bit of forethought about boot loaders is needed, but that’s been the way it’s been done for at least the last 20 years.  It’s also quite handy when all of a sudden (as in I just bought a new piece of gear), I need 1/2 pps or 22 1/3 Hz or some other strange output. No new PC board to lay out. Nothing to buy. Just spend a half hour shooting some new code. 

At least where I have worked, we stopped doing complex stuff with random logic a long time ago. Stuff either moved to custom ASIC’s, PLD’s (CPLD’s, FPGA’s …), or to MCU’s. That started in the 80’s and pretty much was a done deal by the mid 90’s. With > 20 years of data, it’s pretty clear that the programmable approach is at least as bug free and indeed more reliable than the random logic approach.


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