Basic knowledge of HDMI

Reprint http://blog.csdn.net/xubin341719/article/details/7723725

Speaking of Android HDMI, from Android 2.2, android2.3 to android4.0, Samsung's chip has also done 3sc2440, s5pc110, s5pv210, s5pv310 plus new case four-core Samsung Exynos 4412, all become Samsung specialized, but Samsung chip HDMI this piece do is still very good. Big problem is not, is to solve some bugs, no sound, image resolution is wrong ... So the real code I did not see so much, first write an HDMI basic article, look at the back there is no patience to look at this piece of code side. (In fact, most of my work notes, such as I do not understand the words also ask everyone ...) ）

I used to do a period of time television, this HDMI still know point, but the time is long ... So I often write my work notes. Some time ago we Samsung Exynos 4210 platform HDMI no sound, I asked a colleague, is found after he said "What HDMI IIS, codecs related things", I heard a little dumbfounded, always feel wrong, but can not think of it there is not right, the schematic found a pass , did not find AH. Finally found himself SB, video, audio transmission on the same data line, or the original feeling right, ah or do TV, its code feel right.

Let's start with a picture, so be clear and see where the sound is transmitted from:

first, the basic knowledge of HDMI

HDMI (High-definitionmultimedia Interface) is also known as the high-definition multimedia interface, is the first to support transmission on a single cable, non-compressed full-digital high-definition, multichannel audio and intelligent format and control command data number Word interface. The HDMI interface was developed by Silicon Image USA, a joint team of eight renowned consumer electronics manufacturers, including Sony, Hitachi, Panasonic, Philips, Thomson, Toshiba, etc.

second, the HDMI transmission principle

HDMI uses TMDs (timeminimized differential Signal) to minimize transmission differential signal transmission technology, TMDS is a differential signaling mechanism, the use of differential transmission mode, is a use of 2 pin between the voltage difference Technology to transmit the signal. Each standard HDMI connection includes 3 TMDS transmission channels for data transmission, and 1 separate TMDS clock channels to ensure the uniform timing required for transmission. within a clock cycle, each TMDS channel can transmit 10bit of traffic. This 10bit data can be composed of several different encoding formats.

Terminology used:

HDMI to divide the video signal into R, G, B, H, v five kinds of signals with TMDS technology code.

TMDS: These three channels transmit R, G, b Three primary colors, the HV code in the B signal channel inside the transmission, R, G redundant locations used to transmit audio signals.

DDC: The display data channel, used to send configuration information and data format information to the video receiving device, the receiving device reads these

E-edid (Enhanced extended display recognition data).

CEC: The consumer electronic control channel, through which the audio-visual equipment can be controlled.

third, HDMI data capacity

The clock frequency in the HDMI circuit, in the 1.0 version is defined as 25mhz-165mhz, that is, a TMDS channel can transmit up to 165mhzx10bit=1.65gbit of data per second, 3 TMDS channels can be transmitted in one second 1.65x 3=4.95gbit data, coupled with control data, is represented by the standard method of 4.96Gbps bandwidth, if the ratio of transmission signal is less than 25MHZ,HDMI will use automatic cycle technology to fill the code rate, the signal rate to the level of 25MHz.

If a pixel is used, it is the amount of data that can be transmitted in a second to display 1.65G pixels (a complete pixel information consisting of r/g/b three primary colors).

In the 1.3 release specification, the TMDS connection bandwidth increased from the original maximum of 165MHz to 340MHz, the data transfer rate also increased from 4.96Gbps to 10.2Gbps, can support higher data volume of high-definition digital traffic, if the type B-type two-way

TMDS connection, you can then increase the system bandwidth on this basis.

Fourth, HDMI data transmission

the source encoding format for the HDMI input includes video pixel data (8-bit), control data (2-bit), and packet (4-bit). Where the packet contains audio data and ancillary information data. The data transfer process can be divided into three parts: video data transmission period, island data transmission period and control data transmission period.

Video data transmission period: The HDMI data line transmits the video pixel signal, the video signal is encoded, generates 3 channels (namely 3 TMDS data Information channel, each road 8 bits) altogether 24 bits of video data stream, enters into the HDMI emitter. The 24-bit pixel video signal is transmitted through the TMDS channel, the signal encoding of 8 bits per channel is converted to 10 bits, a minimized signal sequence is transmitted at each 10-bit pixel clock cycle, the video signal is modulated to transmit the TMDS data signal, and finally is received in the receiver.

Fifth, HDMI audio function

Traditional digital audio signal transmission mainly relies on two ways: coaxial cable and optical fiber transmission.

Coaxial cable transmission of digital audio signal is a very mature and high-quality way. This interface standard on the device side of the hardware requirements are low, but in the transmission of high-frequency signal, prone to relatively large attenuation, affecting the final sound quality.

Optical fiber to the device reception, transmitter synchronization requirements are very strict, technically than coaxial to be difficult to achieve, but the optical fiber technology in the long-distance transmission advantage is very obvious, there will be no long-distance coaxial cable attenuation too large problem, so also got a lot of distance restrictions and new decoration users of all ages.

HDMI technology combines the advantages of both: the physical layer uses a mature cable connection. HDMI can theoretically achieve a maximum of 20 meters of lossless digital audio signal transmission, those who are required to distance users can also be better accepted.

Sixth. HDMI interface type

Common HDMI types are a, B, and C three types. The type A is a standard 19-pin HDMI interface with the highest penetration rate. The B-type interface is slightly larger, but has 29 pins that can provide a dual TMDS transmission channel. While the C-type interface and the A-type interface have the same performance, the body

Smaller and more suitable for use in compact portable devices. Interface A, interface B, interface C

Seventh. features of HDMI

1, better anti-jamming performance, can achieve the maximum length of 20 meters without gain transmission.

2, for large-size digital flat-screen TV resolution optimization, compatibility is good.

3, Support EDID (note 1) and DDC2B (note 2) standard, the device can intelligently choose the best matching connection mode.

4, has a strong copyright protection mechanism (HDCP (note 3)), and effectively prevent piracy phenomenon.

5, support 24bit color deep processing, (RGB, Ycbcr4-4-4, ycbcr4-2-2).

6, the interface volume is small, all kinds of equipment can be easily installed.

7, a cable to achieve digital audio, video signal synchronization transmission, effectively reduce the use of cost and complexity.

8, fully compatible with the DVI interface standard, users do not have to worry about the old and new system mismatch.

9, hot-swappable technology is supported.