HDCP Receiver Issues
- If your sink has an HDMI HDCP receiver, ensure it can interoperate with a DVI HDCP transmitter.
- Don't assume that all HDMI transmitters support HDCP. Make sure your sink functions with HDMI non-HDCP transmitters.
- Ensure your HDCP Ri register supports both long and short reads. Most sources do long reads, but your sink may encounter a source that is tweaked for performance and therefore will want to read your HDCP Ri register using short reads.
HDCP Repeater Issues
Repeaters are probably the most difficult products to design. That contributes to the difficulty in finding a fully HDCP-compliant repeater today. Compliant repeaters exist, but what we typically find is varying degrees of non-compliance - ranging from "dangerous" to "almost perfect."
The most dangerous repeaters forget to re-encrypt HDCP content. Other repeaters forget to forward hot-plugs to upstream devices, a behavior that can lead to loss of signal especially when switching between inputs.
Because source devices are not required to support repeaters, most repeaters on the market today purposely set their repeater bit false and masquerade as no-output presentation devices. Repeaters that properly announce themselves as such, sometimes forget to pass all downstream BKSVs to upstream devices " so they can be checked against the system renewability message (SRM). They also sometimes forget to indicate MAX_DEVS_EXCEEDED or MAX_CASCADE_EXCEEDED, when conditions warrant. The result is that HDCP's renewability system is again compromised.
To design a compliant repeater with the repeater bit set to true, ensure that your design is compliant and robust. To do this, you must test rigorously. Here are some additional issues to pay attention to:
- Make sure that your repeater behaves correctly in the presence of multiple format-switching sources and hot-plug-generating sinks.
- Don't transmit HDCP content to "hidden" receivers; all downstream BKSVs should be made visible to upstream devices.
- Don't transmit HDCP content to non-HDCP (or revoked-HDCP) receivers operating alone or to a splitter in parallel with a HDCP receiver.
- Don't encrypt non-HDCP content from non-HDCP sources.
- Cycle repeater power for each setup and make sure that your system recovers.
- Make sure HDCP recovers after your repeater switches from one source to another (with a different timing) and back.
- Make certain that your repeater detects and forwards all hot-plugs to up-stream devices, even if the hot-plug signals only last for 100 milliseconds.
- When receiving, decrypting and re-transmitting HDCP content, make sure that re-transmitted HDCP content is re-encrypted. If HDCP content is re-transmitted over another interface, ensure the re-transmission is protected using an equally robust encryption method according to rule #2 previously discussed under "The Basics" above. For example, if you intend to decrypt, scale, compress and send protected content across a LAN to a display device, the content must be ciphered at every step along the way.
- Make sure your list is big enough when building a timing list from data extracted from downstream EDIDs. Recent changes in the CEA-861 standard enable sink devices to declare support for all timings listed in the 861 standard.