This project implements a simple HDMI test device. The intent is to allow
validation that an HDMI source under test is sending a valid HDMI signal,
and that the signal has the expected properties. This can validate both
the HDMI source hardware, as well as any driver/software stack present on
the device. This may be useful for automated driver regression testing.

Intended features are:

* Attach to an HDMI source, act as an HDMI sink, and provide measurement
  of various HDMI signal properties:
  - HDMI clock (implemented)
  - HDMI VSYNC and HSYNC frequency, polarity, and pulse width.
  - ? Measurement of active video area.
  - ? Analysis of active video data. Checksum? QR/... code extraction?

* Attach to a control device to allow:
  - Download of EDID content to provide over the HDMI port (implemented).
  - Control over the HDMI HPD (hoptplug) signal (implemented).
  - Retrieval of signal measurements (implemented for implemented
    measurements)

Currently, this project targets the Scarab Hardware[1] miniSpartan6+[2]
FPGA board, since that's what I have. I've modified the board so that
the HDMI HPD line is driven directly by an FPGA output, rather than
hard-connected to the source's HDMI +5V line. This allows control over
the HPD signal.

Limitations:

Unfortunately, it looks like the Spartan6 PLLs can't run fast enough to
generate the HDMI bit (not pixel) clock for a max-rate HDMI pixel clock
(165MHz pixel clock -> 1650MHz bit clock). Still, this board is enough to
prototype the idea.

[1] http://www.scarabhardware.com/
[2] http://www.scarabhardware.com/product/minispartan6-with-spartan-6-lx-25/