The Hpd__linux of LINUX:HDMI drivers

HPD (hot Plug detection), in a pair of HDMI connections, designed for the realization of thermal plug. Simply put, when the sending end is connected to the receiving end, the receiver will respond to the HPD signal to the sender, and then the sender will start the DDC channel, and read the received EDID information, and then HDCP interaction, if the two sides of the successful authentication, then the video, audio normal work, or join failure, different systems will have different processing.

For example, if the EDID information does not support HDMI, the sender will only send video information, and no audio information, this time the HDMI is only the equivalent of DVI; if HDCP authentication is unsuccessful, some systems may appear snowflakes screen and noise, and some systems will be high resolution (1080I, 720P) reduced to low resolution (480I, 480P) output, so that HDTV is no longer HD, and become a normal SD.

An Important element to proper interpretation of the EDID is ' hot plugging '. The following presents a recommendation for achieving consistent results-a hot during event.

DVI 1.0 Define a HPD signal function that indicates to the host whether a monitor is connected. HPD is designed to being powered by the DDC +5v coming from the host, and to be independaent of whether of the "monitor is" powere D or not. In this way, a host device can detect the monitor and read their characteristics from EDID without the monitor being powered . On a PC, this is feature allows the system to load the correct display configuration without delaying the boot process.

In HPD serves as a indication that EDID are available to be read, however HPD may also have AL Ternative uses. It does no imply any other state of readiness. The relevant definitions from the DVI 1.0 specification are:

A. Hpd-signal is driven by monitor to enable the system to identify the presence of a monitor;

B. The monitor is required to provide a voltage of greater than +2.4v on the HPD pin of the connector only when the EDID D The ATA structure is available to being read by the host.

Implementation Notes:as A example for hot plug support, a simple monitor implementation of HPD support-could be a pull u P resistor to the EDID power supply. After HPD goes active, the host was only expected to read EDID and determine this a valid display mode is available and SUP Ported.

Note---Whenever the EDID information in a device changes to any reason (e.g. if the EDID was updated, or is capable of D ynamically changing its information content), the receiving device pulses-HPD for at least 100ms. This recommendation follows from the HDCP repeater implementation requirement, HDCP repeater pulse HPD low for at LEAs T 100ms to indicate the connection of new device or disconnection of a existing one.

Here is just a summary of the talk, followed by its contact EDID and HDCP in detail.

Link: http://blog.csdn.net/linweig/article/details/5518858