Calypso/audio interaction

Michael Spacefalcon msokolov at ivan.Harhan.ORG
Tue Feb 4 00:06:19 CET 2014

David Matthews <mail at> wrote:

> Making a general purpose distro such as Qtmoko loadtools capable is likely to
> be a non starter.

I agree in general, but see below for some finer points.

> it's likely to be advisable to rip out all the audio stuff also. 

That's where I need to provide some clarification.  The issue here is
that (as David discovered experimentally) the combination of
{Neo FR loudspeaker enabled} + {headset jack Calypso access enabled}
is rather unkind on the loudspeaker, and on the operator's ears.
(Look at the audio circuits in the public GTA02 schematics to see why.)
However, the take-away should NOT be "all audio is bad when doing any
Calypso hacking" - instead it can be fine-grained:

1. One needs to ensure that the loudspeaker amplifier is off when
   using loadtools via the external serial cable method.  But the
   state of the audio subsystem absolutely doesn't matter if you are
   running loadtools from the AP and are *not* enabling the "download"
   channel via /sys dingling.

2. In some advanced debug scenarios (and I do mean advanced, as in you
   actually digging in / debugging the guts of the GSM protocol stack,
   and not just flashing prebuilt images from my FTP site) it can
   actually be quite useful to have the headset jack Calypso access
   channel enabled (with the cable going to the FC developer's laptop
   running rvtdump/rvinterf/fc-tmsh etc) while the modem is running
   "normally", even during a phone call.

If you need to debug the Calypso via TI's RVT/ETM interface (presented
on the 2nd UART wired to the headset jack on the Neo) *while the modem
is making a phone call*, it is possible to have this "download" (or
debug) serial channel enabled while audio is also enabled at the same
time.  The trick is that in this scenario, the audio must be routed to
the earpiece speaker, and *not* to the loudspeaker, and most certainly
not in the "analog headset" mode.

This latter scenario is where FreeCalypso tools do need to play nicely
with Qtmoko/SHR/etc - it would be very useful to observe the RVT/L1/G23
debug output from the modem on the external serial port (or to send
active ETM commands to it via the same interface) while it is being
driven "normally" by Qtmoko/SHR/etc.

> Better idea - use the "special distro" (I used Qtmoko as a starting point)
> with or without the cable - or else build your own single purpose
> boot_and_run_from_sdcard system.

Yes, for loadtools operations (saving FFS dumps, flashing different
firmwares, coming-soon "in vivo" FFS/IMEI editing kit) David's offering
seems like a better choice.


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