How can I check that I have proper communication between SigmaStudio and the SigmaDSP hardware?

The easiest way to do this is to try downloading a program, and then reading back a register with known contents. For example, the DSP core control register:

  AD1940/AD1941: address=0x2642, contents=0x42 0x00
  ADAU1701/ADAU1702: address=0x2076, contents=0x00 0x1C
  ADAU144x: address = 0xE228, data = 0x00, 0x01

If this fails, check that the communications link has properly been established in the Hardware Configuration Window. When SigmaStudio is plugged into the hardware and properly recognizes the driver, the Communications Channel block in the design will turn from red to white. If this block is orange, then you may have one processor properly connected, but another may still be disconnected.