I habe a problem with USB since ages. Now I want to ask if someone knows the problem.
I need to send sms with my Pi. First I had an USB Stick from Huawei (E1750c) to do the job. But it was working badly. At some time it was working well. Then... at any random point (from minutes to days) later it just was not 'responding' anymore. The port /dev/ttyUSB0 was still there. But Gammu was always telling me "Error while opening device. Unknown, busy or no permission" (something like that). I had to reboot many times and somewhen it was working again... for some time.
After reading and reading I gave it it's own 3A power source. But nothing changed. Then I added 2 1000uf capacitors. No real change.
Now finally I changed it to an Sim800L Module. I added it today (via ftdi usb to serial adaptor). At first it was working like a charm and I had hope that the problem is solved now. But I just got the same error from Gammu.
But in the same time I have now a Python script to communicate with the Sim800. And there is some kind of communication possible. When I send "AT" I get - not always - an "Ok" back. Sometimes just nothing comes back.
I also have another serial2usb device attached to the Pi (/sev/ttyUSB0). And some other sensors.
Is there any known problem with long term usage of serial devices at the Pi? Or problems with several serial devices (connected via usb)? Or is it maybe related to Gammu? Or problems with GSM modules?
I really don't know anymore.
PS: Just found this in the log file of gammu:
[System error - failed to lock device, probably opened by other process, 11, "Die Ressource ist zur Zeit nicht verfügbar ('recource is not available at the moment')"]
But there is no other process which is using this device. I am sure of that.