MC7455 'Call Failed'

Bjørn Mork bjorn at
Thu Jun 22 20:22:15 UTC 2017

Tim Harvey <tharvey at> writes:

> What is the purpose of the two QMI+WWAN interface pairs in these modems?

Enabling concurrent connections to more than one APN before the qmap
muxing feature was added. All Sierra QMI modems I have worked with have
had this, starting with the MC7710.

Side note: There are actually 3 pairs.  But I've never gotten the 3rd
channel to work on any of the modems, so it was disabled in the driver a
long time ago.  And with the MC74xx generation they made it officially
non-functional.  I believe it is even disabled in the AT command
interface now, preventing you from easily enabling it in the firmware.

The two first channels work fine. 


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