UART lockup in 7.43 - a known issue with fix?


I am not currently using an Open AT application but we selling moderate numbers of the Xtend FXT009 modem for use with a product that dials a GPRS connection, negotiates a PPP connection and then runs its own IP stack.

We have had several reports from customers, which I have now duplicated, of the modem’s main RS232 port locking up. I am not sure if this is always the case but I have seen it happen when a PPP session is being shutdown. When this happens the modem is still online and registered and you can communicate with it via the USB port. Via that interface I can see it still thinks there is a GPRS connection active.

In this state the modem will not talk at all on the RS232 port no matter what baud rate or state of the handshaking. The only way to get the serial port alive again is to reset the modem or power cycle it.

This problem seems to be more prevalent on some networks/APNs than others although I do not have enough reports to draw conclusive patterns.

Is anyone out there aware of this problem, the cause and a solution please? I cannot see anything like this being fixed in the firmware revision history.

I have tried running a modem with firmware 7.47 and so far I have not seen the problem reoccur whilst using it, but I would like to know a definite problem has been fixed before recommending users upgrade their firmware.

Andrew S


I am chasing a similar issue with a Q26 Extreme (OpenAT 7.46). The issue I have is the CTS line being asserted by the modem and staying asserted until it is reset. I am not using FCM or OpenUART so the OS is in complete control of the buffers and flow management.
When your unit locks up is the CTS line asserted? If it is connected to a PC you can use the attached .Net program to see the pin states.


I will check this - I will need to get a modem in the locked state again before reporting back…

BTW in our case we are not using handshaking (AT+IFC=0,0). The baud rate is only set at 9600 baud though and no data is being transferred when the connection breaks so this problem is not a buffer overrun issue.

The modem is also set to AT&D2 and I noticed that even if the serial port is unplugged or DTR set low that modem does not hang-up the GPRS connection, as it should…