Copying data from unmanaged buffer to local array

[David Smith]

I'm trying to copy data from an array that's created and filled by an
external DLL into a local managed array. The basics are something like:

ushort[,] localArray = new ushort[columns, rows];
IntPtr unmanagedBuffer = IntPtr.Zero;

// Note: I can't pass in a pointer to my array.
// The DLL creates its own buffer which it passes back.
// Image size is set through other commands.
Controller.AllocateBuffer(Device, ref unmanagedBuffer);

// This command would actually store the image in the buffer pointed to
// by unmanagedBuffer
Controller.ReadImage(Device, imageNumber);
I then want to copy the array from the unmanagedBuffer to the
localArray. I can do this at present by looping through the array
elements and doing a Marshal.ToInt16 on each one, but speed has become a
major factor. It takes 3 ms to complete the ReadImage function, but 750
ms to complete a looped copy, and that's just way too long (300 frames
would take about 1 second to read, but almost 4 minutes to copy).

I've tried to figure out how to just use Marshal.Copy for this, but it
always tends to run into some exception. Is there a way to do the
equivalent of a fast memcpy here?

--
David