Guidelines and rules for drivers

The following are guidelines and rules for writing areaDetector drivers

  • Drivers will generally implement one or more of the writeInt32(), writeFloat64() or writeOctet() functions if they need to act immediately on a new value of a parameter. For many parameters it is normally sufficient to simply have them written to the parameter library, and not to handle them in the writeXXX() functions. The parameters are then retrieved from the parameter library with the getIntParam(), getDoubleParam(), or getStringParam() function calls when they are needed.

  • If the writeInt32(), writeFloat64() or writeOctet() functions are implemented they must call the base class function for parameters that they do not handle and whose parameter index value is less than the first parameter of this class, i.e. parameters that belong to a base class.

  • Drivers will need to call the createParam() function in their constructor if they have additional parameters beyond those in the asynPortDriver or ADDriver base classes.

  • Drivers will generally need to create a new thread in which they run the acquisition task. Some vendor libraries create such a thread themselves, and then the driver must just implement a callback function that runs in that thread (the Prosilica is an example of such a driver).

  • The acquisition thread will typically monitor the acquisition process and perform periodic status update callbacks. The details of how to implement this will vary depending on the specifics of the vendor API. There are many existing detector drivers that can be used as examples of how to write a new driver.

  • If the detector hardware does not support fixed-period acquisition or muliple-image acquisition sequence (ADNumImages parameter) then these should be emulated in the driver. The simDetector, marCCD and other drivers can be used as examples of how to do this.

  • If NDArrayCallbacks is non-zero then drivers should do the following:

    • Call asynNDArrayDriver::getAttributes to attach any attributes defined for this driver to the current array.

    • Call doCallbacksGenericPointer() so that registered clients can get the values of the new arrays.