MCSI breakthrough

Mychaela Falconia mychaela.falconia at
Thu Mar 28 18:44:20 UTC 2019

Hello FreeCalypso community,

For those with an interest in the embedded modem side of our family of
projects, I have some exciting news: after having it on the back burner
for almost 2 y since our first boards, I finally got MCSI to work in
an acceptable manner as a digital voice interface.  The details are
documented in the new Calypso-digital-voice article in the
freecalypso-docs Hg repository, but here are the two essentials:

* As verified by hooking up 3 channels of my Rigol scope to MCSI_CLK,
MCSI_FSYNCH and MCSI_TXD signals simultaneously (all 3 are outputs
from the Calypso in the "Bluetooth" digital voice mode), I have
confirmed that the framing format in which the digital voice samples
are exchanged is indeed what I thought it was - please read my
Calypso-digital-voice article in freecalypso-docs for the details.

* The key to having MCSI work successfully as a practically usable
digital voice i/f is that it must not be enabled continuously, instead
it requires dynamic control: it needs to be turned on when a voice
call is connected and turned off when a call ends, so that MCSI clocks
are running only when the modem is in an active call, and not during
idle between calls.  As explained in my Calypso-digital-voice article
in freecalypso-docs, I have just implemented a new mechanism in our
Magnetite and Selenite firmwares (enabled with the new AT at VSEL=1
command) that does the necessary auto-switching magic, and with this
new firmware feature the digital voice interface works reliably: the
DSP bug that was previously getting in our way is reliably avoided.

So if you have an FCDEV3B and you are interested in getting a digital
voice interface out of your modem, you can now give it a try.  You
will need to compile the latest FC Magnetite firmware in the hybrid
configuration (I plan on putting out a new official build in the next
few days), and you will need to read the Calypso-digital-voice article
in freecalypso-docs for the hardware interface details.

Hasta la Victoria, Siempre,
Mychaela aka The Mother

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