Re: Quectel EC21 with internal GSM MUX

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Hello Martin and Denis!

> Could it be hardware flow control that not configured right on either
> end? I remember having issues with both swapped cts/rts lines, and =
with
> floating signals (i.e. halt/flow state could change by putting a =
finger
> on the board).

Thank you for this hint! CTS and RTS should be set up properly. I have =
not seen (unexpected) glitches in any recording of the serial connection =
between modem and the host controller so far. There is a small pulse on =
nCTS after switching from plain AT communication to GSM 07.10 muxing and =
while "pressing the power button". The former seems like normal behavior =
from the modem while switching protocols - the latter I have ignored so =
far as they happen after the initial failed initialization.

I uploaded two screen shots to [1] and [2] and just in case you want to =
look at the huge Saleae Logic [3] capture with analog data you can find =
it at [4] or another system startup without analog data at [5].


My next step is to strace oFono's interaction with the serial interface =
to the modem. Do you have a bespoke configuration for strace? Let's see =
what this reveals. I expect so see the calls to poll which I did not got =
from just instrumenting oFono.


Best regards,

Christian

--=20
[1] =
https://christian-meusel.de/share/3536ce67db07de020d6b5b8fa6fe70422cf85c93=
107f9944debae488339fa61e/20251023-1839-6.1-omux-o6d8c-analog-overview.png
[2] =
https://christian-meusel.de/share/3536ce67db07de020d6b5b8fa6fe70422cf85c93=
107f9944debae488339fa61e/20251023-1839-6.1-omux-o6d8c-analog-cts-glitch-at=
-mux-activation.png
[3]=20
[4] =
https://christian-meusel.de/share/3536ce67db07de020d6b5b8fa6fe70422cf85c93=
107f9944debae488339fa61e/20251023-1839-6.1-omux-o6d8c-analog.sal (about =
800 MB)
[5] =
http://christian-meusel.de/share/3536ce67db07de020d6b5b8fa6fe70422cf85c931=
07f9944debae488339fa61e/20251023-2052-6.1-omux-o6d8c.sal (few KB)=

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