We got Sound!!!

[Paul Mansfield]

TLDR:
* my TCM does have working sound. yay! though it's not stable, it's
100x better than it was.
* my headphone socket works just fine
* my speakers, or the speaker amplifier is faulty.

Boran (with whom I work) is back from holiday tomorrow. We will pop
the back cover off and look for a problem. I'll take my camera to work
and see if I can get some decent pictures at the same time.


Full story:

Good news and bad news. Copying linux to the eMMC may or may not have
helped. I used the c6-off/c7-on script and that has made it possible
to get sound in linux without instant crash! Yay!

However, I still suffer serious occasional crashes when the sound
driver is loaded - never with driver not loaded/blacklisted. When
these crashes happen, it's as if there's a total power failure, the
screen goes black, and the TCM becomes unresponsive as if it's off. I
still have to forced a power cycle by holding power for 20 seconds to
turn it off. When I turn it back on, it has lost its CMOS settings and
I have to set the time and date!

So, the first time I booted to test these settings, last might, I got
the whole black screen of death crash when I tried to play a youtube
video.

The second time, it didn't crash, and I was able to play a music
video. At first there was no sound, then I realised it was very very
quiet. I cranked the volume up and all I could hear was distorted but
still faint sound from the speakers. I turned the volume down to mid
way and went through all the mixer settings and tried unmuting all the
ones that didn't cause feedback from the microphone input, but no
luck. This morning I tried the headphone socket, and that worked once
I unmuted the correct channels, and the sound was loud, clear and
good.

I booted Windows and I couldn't get the speakers to work on that
either. I used the Intel driver update utility in case my upgrade from
W8.1 to W10 had resulted in out of date drivers.

Sadly, there was no sound driver to update*. To be honest, I can't
remember the last time I used the speakers. I know from postings on
the Asus Transformer group and elsewhere that people have blown their
speakers up on devices with this Baytrail SoC in it, I presume because
there's no DC blocking capacitors or something, one person reported he
got smoke out of his computer :-(


* their tool did tell me my video driver was out of date but it had
vendor-specific tweaks and therefore Intel's tool wouldn't update i.