All I/O functions must be initiated with DRV_DeviceOpen, which opens a device via Device file to return the driver handle of the device. With the driver handle, user can use the device to perform I/O operations by calling various functions. Call DRV_DeviceClose to finish the operation and free the resources allocated by DRV_DeviceOpen.
The calling flow is shown as below:
Device file specifies the device on which you want to perform the I/O operations.
For example, a device has association with a device file "/dev/advdaq0"
using advdevice_bind utility. You can assign the device file "/dev/advdaq0" to the function DRV_DeviceOpen
directly.
DRV_DeviceOpen initializes the device specified by device file. This function must be called before any other methods that perform I/O operations. DRV_DeviceClose is the counterpart function of the DRV_DeviceOpen function. Its purpose is to close the device.
Driver Handle is returned by DRV_DeviceOpen. It points to the structure that keeps the settings of a device. The subsequent functions require the use of Driver Handle, instead of device file, to represent the desired device.
Each driver function returns an Error Code that indicates whether or not the function was performed successfully. If the function has failed to perform, it will return a code that is non-zero. The error code may be passed to the DRV_GetErrorMessage function to retrieve its error message.