Q2501 generates errors with FixNow functionality



I am using a Q2501B modem in my application.
I have already designed this GPS/modem into my application, but I am running into problems now that I want to use the GPS Lowpower features.

According the documentation, the Q2501 is using a ublox Antaris based GPS receiver.

Problem 1:
When I want to check/enable the uBlox and NMEA protocols using the $PUBX,41 message, I get a uBlox warning message: PUBX 41 unknown msg. While this message is listed in the Antaris protocol specification.

Problem 2:
When I configure the GPS FixNow functionality using the uBlox CFG-FXN message with the parameters:
(copied from an example listed in the uBlox manual)
Ton = 0 sec, Tacq = 60 sec, Treaq = 5 sec, Toff = 60 sec, Tacq_off = 120 sec, Treaq_off = 60 sec. Absolute align = disabled, Base TOW = not used.

The GPS receiver ACK’s the contents of this frame.
When I send an uBlox CFG-RXM msg, with GPS mode set to Auto, LP mode set to Fix Now.
This msg is ACK-ed by the GPS Receiver.

However the GPS then sends a uBlox INF-NOTICE: Resetting GPS.
After this message all SV and time data are not initialized anymore.

The GPS receiver had a valid position fix, at the time the FixNow settings
where configured. The position fix got lost, as soon as the FixNow mode was enabled, and the GPS reported a reset.
After this reset the GPS receiver was unable to get a position Fix (read any SV and Time) in the 8 minutes that I gave it.

I then send a CFG-RXM msg to re-enable the continues mode again. (the message was ACK-ed)
6 minutes after this, the GPS receiver was still unable to get a position fix.

I then turned off the Power to the Q2501, and turned it back on again.
The GPS receiver now obtained a postion fix in about 60 seconds.

Problem 3:
The description is similiar to Problem 2, except when the GPS receiver reports a INF-NOTICE: Resetting GPS, the CFG-RXM msg with the FixNow command is sent again.

The GPS receiver still is unable to get a position fix, but it now reports:
a uBlox INF-WARNING: schd task overrun 02000000
message at specific intervals.

Changing the Q2501B from the development board, with one of the Q2501B modems from the null series, did not give any other results.

My hardware and software versions:
Starterkit Q2501 V2.0 (I am currently testing with the starter kit)

Hardware Version 3.12

reported by the uBlox protocol of the GPS:
ANTARIS ATR0620 HW 00000040
EXT CORE 3.0 Feb 11 2004 13:59:43
INT EXT0 (RCV) WVCM0.1 Mar 10 2004 16:28:50

I am using the GPS Main serial link UART2.

Has anyone seen this kind of behaviour before ?
Does anyone use the FixNow functionality of the Q2501B ?

Can someone please help me ?

Best Regards,

Robin Stevenhagen