@ladyada says:
"having this be adjustable (reference) would be ideal cause you can get
absolute voltages but for now, VCC/4 + 4x matches every other chip :)"
... and indeed doing it this way happens to give a much more steady
reading when using a VCC-referenced resistance, and so many of the simple
things you'd wire up are actually VCC-referenced anyway.
Make changes in asf4_conf even though I think in these cases the
"peripherals" submodule is running the show.
Arduino clocks the DAC at 12MHz but uses the CCTRL setting for
clocking < 1.2MHz (100kSPS).
A fresh clock (6) is allocated for the new 12MHz clock. This matches
the Arduino value, though not the GCLK index.
Modify other settings to more closely resemble Arduino.
In AudioOut, actually clock the waveform data from the timer we set up
for this purpose.
This gives good waveforms when setting AnalogOut full-scale in a loop,
but the rise/fall of waveforms that come from AudioOut are still erratic.
Weirdly, if AudioOut limits its range even slightly (e.g., to 1000..64000)
then the erratic
Note that this will require https://github.com/adafruit/samd-peripherals/pull/26
to be accepted for the submodule update here to work.
.. based on some tasks I found that caused stuttering:
# Test SD and printing
while True: os.listdir('.')
# Test bulk I/O
while True: len(open('somefile.wav', 'rb').read())
Each of these tasks *WAS* worse and I am improving them in a separate
PR by adding RUN_BACKGROUND_TASKS to them.
This enables the highest level of debug symbols, and all optimizations
except lto that do NOT interfere with debugging, in the view of the gcc
maintainers.
Testing performed: I used a Particle Xenon with a HDA1334 I2S DAC.
I played a variety of mono 16-bit samples at 11025 and 22050Hz nominal
bit rates. With this setup, all the 11025Hz samples sound good.
I tested play, pause, and loop functionality.
During some runs with 22050Hz samples, there were glitches. However,
these may have only occurred during runs where I had set breakpoints
and watchpoints in gdb.
I also tested with a MAX98357A I2S amplifier. On this device, everything
sounded "scratchy". I was powering it from 5V and the 5V rail seemed
steady, so I don't have an explanation for this. However, I haven't
tried it with a SAMD board.
