Today, I re-read previous suggestions and stopped to ponder this one:

Wed, 13 Jul 2016 10:19:50 -0700, AK <00@case.edu>:

    For square wave generation I would use the PWM unit with 50% duty cycle=
 for
    lower frequencies, and the numerically controlled oscillator peripheral
    (NCO) for higher frequencies.  You could even use a CLC to switch betwe=
en
    them seamlessly.  You don't want to waste time farting around with bit
    banging and instruction-bound delays. It takes a bit of reading and tes=
ting
    to use one, but then the updates to frequency are fast and simple, and =
you
    can spend processor cycles calculating the next update, servicing other
    routines, etc.

Joe suggested sampling and storing the actual sweeps generated by Audacity,=
 timing 112 pulses in blocks. Sergey kindly put forth his C code involving =
log(f), but it would probably take me longer to figure out how to convert t=
hat to ASM than to use another approach.  Denny offered several approaches,=
 the simplest seeming to be the use of look-up tables without the need for =
interrupts (which is similar to Joe's suggesting of storing actual waveform=
 values).  And then we have the above suggestion of using a combination of =
PWM and NCO with CLC to switch between them.  But why use the PWM module si=
nce the NCO module can accommodate the entire frequency range of the sweep?=
  What is the advantage to using both PWM & NCO together?  That would seem =
to add to program complexity, especially when you factor the CLC setup requ=
ired to switch between the two.  More on the CLC here:

http://ww1.microchip.com/downloads/en/DeviceDoc/41631B.pdf


For now, I have an ASM program running on actual hardware that uses the NCO=
 and CWG to feed my H-BRIDGE and 8-ohm speaker with a duo-tone sequence of =
625Hz for 600ms followed by 825Hz for 600ms, repeating.  You can see the co=
mplete Assembly code for that here:

https://cl.ly/1M3I3Y2L1421

It does not contain a sweep though.  I wrote that code merely to verify my =
NCO and CWG initialization routine works flawlessly. I verified the CWG out=
put pins on a scope and also confirmed it by listening to the speaker. The =
frequencies quite accurate, and my 1.5us of dead band is also correct as we=
ll.=20

Honestly, creating the sweeps are the hardest part. Fixed tones are easy to=
 implement as you can see from my code.  But since there are different ways=
 to implement sweeps on a 16MHz 16F1508 (from Joe's suggested sample-and-st=
ore to using PWM+NCO), I am now mulling the absolute simplest approach that=
 still sounds acceptable to the ears.

Once again, thank you for your kind help and input.

James


--=20
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