Questions.txt

We are working in a multiple camera setup. Cameras may be connected and
disconnected many times during the lifetime of the caller application. Cameras may
disconnect because of EMI, power or cable failure, and we need robust
ways to handle disconnects and remediate.

Setup is Ubuntu 18, we have been testing a lot of your versions of the SDK, up to 20.8.26.

* we find no function in the SDK for determining if an opened camera [OpenQHYCCD(CameraName);  InitQHYCCD(camhandle)]
is still reachable. Parameters can be read with GetQHYCCDParam() with a formerly valid camhandle, even if the cable of the camera has been pulled.

* Calling ScanQHYCCD() after communication with a camera is opened, makes that camera unreachable.

* we find no function in the SDK for determining how many cameras have been opened. Knowing that at least one camera is opened is necessary, to prevent calling ReleaseQHYCCDResource() too early.

* the caller application segfaults with the following trace if a camera is opened 
[OpenQHYCCD(CameraName);  InitQHYCCD(camhandle)], closed [CloseQHYCCD(camhandle)] and reopened again. What is going on?

  Stack Trace (from fault):
  [  0] 0x00007f1266346de6     /lib/x86_64-linux-gnu/libusb-1.0.so.0+00044518 libusb_control_transfer+00000086
  [  1] 0x00007f12642f8949     /usr/local/lib/libqhyccd.so+00780617 _ZN6QHYCAM7vendTXDEPvhPht+00000229
  [  2] 0x00007f12642fa5b2     /usr/local/lib/libqhyccd.so+00787890 _ZN6QHYCAM10LowLevelA0EPvhtth+00000196
  [  3] 0x00007f12643c1ad5     /usr/local/lib/libqhyccd.so+01604309 _ZN10QHY600BASE12InitChipRegsEPv+00000277
  [  4] 0x00007f12642e9d25     /usr/local/lib/libqhyccd.so+00720165 InitQHYCCD+00000411
  ...

* the caller application segfaults if libqhyccd.so is released before all cameras are closed and ReleaseQHYCCDResource() is called. What resource is left allocated under the carpet?

* Explain the function QHYCCDQuit(). We have seen application crashes if it is not called when a camera is closed. On the other hand, the function has no argument specifying which camera connection is terminated.