Re: SARA-R4 unreliable LTE-M connection problem

[Aleksander Morgado <aleksander aleksander es>]

> Connection can be established, I see data on the modems RX line, but nothing
> on the TX line, which means the host sends data to the modem, but gets back
> nothing.
>
> Can this be a problem with the baudrate? I mean it's a classical serial UART,
> so I would assume baudrates of host and modem must match. In AT command mode
> the baudrate is 115200 and ModemManager can successfuly send AT commands and
> receives reponses. Is it possible NetworkManager and/or pppd change this
> somehow?

Have you tried to set the ID_MM_TTY_FLOW_CONTROL udev tag in the TTY
port so that flow control settings are applied by ModemManager before
the connection is started? E.g. ID_MM_TTY_FLOW_CONTROL set to
"rts-cts" or to "xon-xoff"

Also, if using 115200, have you set ID_MM_TTY_BAUDRATE to 115200 as
well as a udev tag in the TTY port? The default in MM is 57600 really.

-- 
Aleksander
https://aleksander.es