Android HDMI (I): Basics of HDMI

Keywords:Android 4.0 HDMI

Platform information:
Kernel:Linux3.0
System:Android4.0.3
Platform:S5pv310 (Samsung exynos 4210)

Author: xubin341719 (Thank you for reprinting. Please indicate the author.)

Speaking of Android's HDMI, from Android 2.2, android2.3 to android4.0, Samsung's chips have also become Samsung's professional users, including 3sc2440, s5pc110, s5pv210, s5pv310, and Samsung exynos 4412, which is the core of the new case, however, the Samsung chip HDMI is still very good. The big problem is no. It solves some bugs, no sound, and the image resolution is incorrect ...... So I didn't see that much real code. I should write a basic article on HDMI first, and check whether there is patience to look at this piece of code. (In fact, most of my work notes are my work notes. If you cannot understand them, please ......)

I have worked on TV for a while before. I know about HDMI, but it takes a long time ...... So I often write work notes. Some time ago, our Samsung exynos 4210 Platform had no sound HDMI. I consulted a colleague and found out that he was "looking for something related to HDMI IIS and codecs ", I was a bit dumpfounded, and I always thought it was wrong, but I couldn't remember it. I found a channel on the schematic and couldn't find it. I finally found myself sb. The video and audio are transmitted on the same data line. I still felt right. I still had a TV, and the code was right.

Let's take a look at the figure. It is clear that the voice is transmitted from there:

1. Basic HDMI knowledge

HDMI (High-Definition Multimedia Interface), also known as the High-Definition Multimedia Interface, is the first to support transmission on a single cable, digital interfaces for full digital high definition, multi-channel audio, and smart format and control command data without compression. The HDMI interface was jointly developed by silicon image, a subsidiary of eight famous consumer electronics manufacturers, including Sony, Hitachi, Panasonic, Philips, Thomson, and Toshiba.

Ii. HDMI Transmission Principle

HDMI uses tmds (timeminimized differential signal) to minimize the transmission of differential signals. tmds is a differential signal mechanism that uses differential transmission, it is a technology that uses the voltage difference between two pins to transmit signals.Each standard HDMI connection includes three tmds transmission channels for data transmission and an independent tmds Clock Channel to ensure the unified timing required during transmission.Each tmds channel can transmit 10-bit data streams within a clock cycle. The 10 bit data can be composed of several different encoding formats.

Terms used:

HDMI classifies video signals into five types: R, G, B, H, and V and uses tmds for coding.

Tmds: these three channels transmit the three primary colors of R, G, and B, and the HV code is transmitted in the B signal channel. The redundant positions of R and G are used to transmit the audio signal.

DDC: a data display channel used to send configuration information and data format information to the video receiving device.

Information for E-EDID (enhanced extended display for identifying data.

CEC: The consumption electronic control channel. This channel can be used to control the work of Audiovisual Devices.

Iii. HDMI data capacity

The clock frequency in the HDMI circuit is defined as 25mhz-165mhz in version 1.0. That is to say, a tmds channel can transmit up to MHz × 10bit = 1.65gbit data per second, the three tmds channels can transmit 1.65x3 = 4.95gbit data in one second. In addition, with control data, the standard bandwidth is 4.96gbps. If the transmission signal ratio is less than 25 MHz, HDMI uses the Automatic loop technology to fill the bit rate and increase the bit rate of the signal to 25 MHz.

If it is represented by pixels, it means that the data volume needed to transmit and display 1.65g pixels (a complete pixel information consists of three primary colors of R/G/B) in one second.

In version 1.3, the connection bandwidth of the tmds instance has been increased from 340 MHz to 10.2 MHz, and the data transmission rate has also increased from Gbps to Gbps, which can support high-definition digital traffic with higher data volumes, if type-B dual-channel is used

After the tmds connection, you can increase the system bandwidth by a factor of one.

Iv. HDMI Data Transmission

The source encoding format of the HDMI input includes video pixel data (8 bits), control data (2 bits), and data packets (4 bits ). The data package contains audio data and auxiliary information data. The data transmission process can be divided into three parts: video data transmission period, Island data transmission period, and control data transmission period.

Video data transmission period: video pixel signals are transmitted on the HDMI data cable. The video signals are encoded to generate three channels (that is, three tmds data information channels, each with 8 bits) A total of 24-bit video data streams are input to the HDMI transmitter. The 24-bit pixel video signal is transmitted through the tmds channel. Each channel encodes the 8-bit video signal into 10 bits, and transmits a minimum signal sequence at each 10-bit pixel clock cycle, the video signal is modulated into the tmds data signal for transmission and finally received in the receiver.

V. HDMI audio Functions

Traditional Digital Audio Signal Transmission mainly relies on two channels: coaxial cable and optical fiber transmission.

Coaxial cable transmission of digital audio signals is a very mature and high-quality method. This interface standard has low requirements on the hardware of the device, but it is prone to large attenuation when transmitting high-frequency signals, affecting the final sound quality.

The optical fiber has strict requirements on synchronization between devices and transmitting terminals, which is technically more difficult to implement than coaxial. However, the optical fiber technology has obvious advantages in long-distance transmission, the long-distance attenuation of coaxial cables is not too large, so it is also favored by many users with distance restrictions and new decoration.

The HDMI technology combines the advantages of both: the physical layer uses mature cable connections. In theory, HDMI can achieve a maximum of 20 meters of Lossless Digital audio signal transmission, and those who have requirements for distance can also be better accepted.

6. HDMI Interface Type

Common HDMI types include A, B, and C. Type A is the standard 19-pin HDMI interface with the highest penetration rate. Type B interface has a slightly larger size, but has 29 pins, which can provide dual tmds transmission channels. The performance of C-type and A-type interfaces is the same,

Small product, more suitable for the use of compact portable devices. Interface A, interface B, and interface C

 

VII. HDMI features

1. It has better anti-interference performance and can achieve up to 20 meters of non-gain transmission.

2. The resolution of a large-sized digital flat panel TV is optimized to ensure compatibility.

3. Supports the edid (Note 1) and ddc2b (note 2) standards. You can intelligently select the optimal connection mode between devices.

4. Powerful copyright protection mechanism (HDCP (note 3) to effectively prevent piracy.

5. 24 bit color depth processing (RGB, YCbCr4-4-4, YCbCr4-2-2 ).

6. The interface is small and can be easily installed on various devices.

7. A single cable enables synchronous transmission of digital audio and video signals, effectively reducing costs and complexity.

8. fully compatible with DVI interface standards. You do not have to worry about mismatch between the new and old systems.

9. Supports hot swapping technology.