HDMI/DVI HDCP handshake problems & how to avoid them

Looking For Trouble
A recent survey of existing products indicates most HDCP problems have simple causes. This is not to say that troubleshooting such problems is always simple. HDCP handshake problems can be totally bewildering if you don't have the specialized tools necessary to detect root causes. Assuming you have the right tools, here are some problems to avoid and guidelines to follow:

1. HDCP transmitters that don't distinguish between high-value HDCP content and unprotected content will encrypt everything. These source devices won't display anything on a non-HDCP receiver, even if the material being played is an unprotected homemade DVD.
2. There are source products that ignore sink power-cycles, hot-plugs, or reconnects. These sources typically require customers to disconnect and reconnect a cables or power-cycle equipment in order to trigger re-authentication. Sometimes, nothing works. When connecting a source to a repeater, hot-plugs become even more critical as up-stream sources must be informed of all down-stream sink changes. Make sure that your product detects all HDCP-critical sink device state and cabling changes. Make sure your product detects all hot-plugs " even the ones that only last for the minimum 100 milliseconds. Make sure that your source responds to hot-plugs in a timely manner. When you receive a hot-plug, immediately terminate existing display data channel (DDC) tasks and begin a new HDCP handshake.
3. Doing things too fast can lead to blinking video. When your HDMI transmitter drives an HDMI receiver, always mute before changing signal timing and un-mute afterwards. Allow the HDMI receiver some time to detect mute and process the timing change before you remove mute. DVI sources must cease transmission and re-authenticate only after signal timing stabilizes and the receiver has had time to recover. The HDCP circuits in most sinks require stable timing in order to function properly.
4. Ensure that your HDMI HDCP transmitter can detect and drive a DVI HDCP receiver. Pay attention to the HDMI capability in the Bcaps register and switch to your HDMI transmitter to DVI-mode if necessary. Alternately, when you read the sink's EDID, look for an HDMI vendor specific data block (VSPD). If you can't find one, switch your HDMI transmitter to DVI mode.
5. Support repeaters! More consumers are inserting A/V receivers (AVRs) between their source and presentation products. Unfortunately, not all source products support repeaters. The ones that don't cause systems to stop working when the repeater is inserted. In this case, the innocent repeater manufacturer is often blamed.
6. Do not transmit HDCP content to non-HDCP or revoked-HDCP receivers. In the first case, your customers may end-up watching snow. In the latter case, you'll be defeating HDCP's renewability system.
7. Do not transmit decrypted HDCP content. This invites content theft and potential legal action.