Basic knowledge about display driver

For Android display driver, you must have a certain understanding of the basic knowledge of the display, in order to write the driver code more easily!

LCD interfaces include SPI/I2C/mCu/CPU/RGB/mddi/mipi, SPI/I2C for low-speed black and white screen, and mCu/CPU/RGB for parallel port, there were a lot of functional machines used before the smart machines. When mobile phones entered the big screen era, the transmission speed of the parallel ports could not keep up, especially in the face of applications with high-definition playback, which caused the emergence of mddi and mipi, mddi was launched by Qualcomm, and mipi was jointly established by many important manufacturers. It launched a series of mobile standards, including mipi DSI.

 

The launch of mipi is not long, but the promotion speed is very fast, including iphone4/meizum9 using the mipi interface (most of them except for Qualcomm's mobile phones)

 

The mipi interface has physical specifications, so we can see that the Development Board and LCD supporting DSI are both a line of the mipi specification. However, at present, the LCD OF THE mipi interface is basically not available. There are some self-developed and used iPhone screens on the Internet.

In the Development Board Section, the panda board does not introduce the mipi signal on the CPU and cannot be used. The Samsung s5pc100 Development Board does not provide any interface. The Samsung s5pv210 Development Board generally has the mipi interface.

Driver section. Currently, only OMAP code can be found.

 

 

The mipi interface supports Mode 2: video mode and command mode.

The video mode and RGB interfaces are similar. framebufferdriver uses system memory and pixel data is stored in the buffer. The mipi host sends data to the LCD over the DBI bus according to the specified sequence. Because the signal lines and data lines of mipi are reused, the synchronization of time series is actually completed by data package, rather than the level on the signal line as in the parallel port.

In video mode, there is no big difference between the entire architecture and parallel interfaces such as RGB.

 

The command mode requires the LCD module to integrate the LCD Ram. The host sends the display data to the LCD in command mode, and the LCD obtains the data refresh from its own LCD Ram.

 

In contrast, the command mode is relatively power-saving. When the screen is not updated, the mipi bus can be idle. The LCD uses its own ram to refresh the screen, while the video mode needs to continuously transmit data to the LCD, even if the screen does not change

However, the command mode may be insufficient in High-Resolution HD playback on the screen.

 

OLED-Organic Light Emitting Devices, due to their excellent features, such as ultra-wide angle of view, fast response, high contrast, wide color gamut, light and thin, low power consumption, etc, it is considered as the ideal next-generation flat display technology. In addition, compared with traditional TFT display technology, OLED has unique potential capabilities to achieve flexible and transparent display, and is also known as the ultimate fantastic display technology. Compared with TFT, The OLED display has many advantages: the OLED device is a sandwich structure (), the manufacturing process is simple, and the cost of mass production is 20% less than that of TFT. The OLED can emit light on its own, so the OLED is much brighter than the TFT, especially when used outdoors. At the same time, because the OLED does not need a backlight, it not only saves energy, but also can be very lightweight. In addition, the contrast of the OLED is larger, and the color effect is richer. There is no restriction on the perspective range of the OLED. The visual angle can generally reach 170 degrees. The solid-state OLED display provides better seismic performance.

 

The next generation flat panel display technology is similar to and better than TFT display technology. OLED has a very simple sandwich structure, that is, there is a very thin organic material between the two electrodes, when there is electricity flow, these organic materials will emit light. Compared with TFT display, OLED has many advantages: Because the OLED itself can emit light without backlight, The OLED display can be made lighter and thinner, with a larger visual angle and richer colors, and can significantly save energy. The driving mode of OLED display is divided into passive matrix (PM-OLED) and active matrix (AM-OLED. The pixel size of the OLED display can be dozens to hundreds of micrometers, and the display resolution can reach more than 300 PPI (the number of pixels per inch ). Based on these advantages, OLED has been widely used in mobile electronic devices such as MP3 and mobile phones, and has gradually extended to large-size display fields such as PC monitors, laptops, and televisions.

 

TN panel and IPS panel

1. IPS is a hard screen and suitable for touch devices, such as tablets.

2. IPS must win the NT panel in color, so IPs has a color representation that is not available in TN panel. And IPS is just a big concept, which is divided into many models of Panel, such as P-IPs, S-IPs, H-IPS, etc., now generally more than one thousand of the display is the lowest end of the E-IPS, although almost, however, the color is better than TN.

3. The disadvantage of IPS is that the response time is not as short as tn. At this stage, it is positive.

Second, black shows poor IPs, which is visible to the naked eye compared to tn.

IPS is relatively expensive, of course, E-IPS and TN now almost. However, high-end IPs are expensive, ranging from thousands to tens of thousands, or even higher.

Generally, Asus and LG are recommended for IPs display. Samsung does not have IPs, otherwise it should be good.

 

The above describes the materials and technologies of mobile phone screens in the current market. Such as OLED, AMOLED, superamoled, and SLCD are screen materials, while mobile phone manufacturers such as retina, CBD, and ASV have developed some practical technologies on the screen panel, in order to make your product more characteristic, bring different visual feelings to consumers.

Organic Light Emitting Display (OLED) is a new type of cell phone LCD. It is called a "dream display ".

The OLED display technology is different from the traditional LCD display method, without the need for backlight, using a very thin organic material coating and glass substrate, when there is electricity flow out of time, these organic materials will emit light. In addition, the OLED display screen can be lighter and thinner, with a larger visual angle and significantly reduce power consumption.

The differences between OLED and TFT and SLCD/ASV are: the latter is one of the liquid crystal, which requires light transmission to enable the image, while the OLED does not, each of its pixels can emit light. There are two types of OLED: passive driving pmoled and active driving AMOLED.

Pmoled is generally monochrome, and will be small on some mobile phones, such as: a few inches at to display the phone time and status of the secondary screen is pmoled.

 

AMOLED

AMOLED Full name: activematrix/Organic Light Emitting Diode, which can be colored. In terms of display efficiency, AMOLED has a fast response speed, a higher contrast, and a wider angle of view. These are the natural advantages of AMOLED over tft LCD. In addition, AMOLED has its own luminous characteristics and does not need to use a backlight, therefore, it is more lightweight and energy-saving than TFT. There is also a more important feature. AMOLED without a backlight can save 3 ~ of tft LCD ~ The cost of a 4-proportion backlight module is flawed. Compared with other materials, the screen has a higher particle size at the same resolution.

Superamoled

Superamoled Full name: Super active matrix/Organic Light emittingdiode, in the original AMOLED screen with fast response, self-light, outstanding performance and lower power consumption advantages at the same time, the removal of glass covers provides better sunlight display. In addition, Super AMOLED is equipped with mdnie (mobile digital Natural Image Engine) technology to view and respond quickly from any angle. In short, Super AMOLED is an upgraded version of AMOLED. Available models: Samsung i9000 and Samsung S8500.

 

Superamoled plus

Super AMOLED plus (SAP for short), Chinese nickname: Magic screen, uses improved Super AMOLED material, improved the way the previous Super AMOLED screen pentile pixel arrangement, the matrix is more normal and delicate. If it is calculated by pixel, the number of pixels for the new display will increase by 50%, both in contrast and in outdoor readability compared to the previous Super AMOLED screen.

The Super AMOLED, once proud of its predecessors, also features a great deal of scenery. However, in the later stage, it was said that it showed a large particle size and gradually became mediocre. The Super AMOLED plus panel was also launched by Samsung.

 

OLED

Organic Light Emitting Display (OLED) is a new type of cell phone LCD. It is called a "dream display ".

The OLED display technology is different from the traditional LCD display method, without the need for backlight, using a very thin organic material coating and glass substrate, when there is electricity flow out of time, these organic materials will emit light.In addition, the OLED display screen can be lighter and thinner, with a larger visual angle and significantly reduce power consumption.

The differences between OLED and TFT and SLCD/ASV are: the latter is one of the liquid crystal, which requires light transmission to enable the image, while the OLED does not, each of its pixels can emit light. There are two types of OLED: passive driving pmoled and active driving AMOLED.

Pmoled is generally monochrome, and will be small on some mobile phones, such as: a few inches at to display the phone time and status of the secondary screen is pmoled.

 

AMOLED

AMOLED Full name: Active Matrix/Organic Light Emitting Diode, which can be colored. In terms of display efficiency, AMOLED features fast response speed, higher contrast, and wider viewing angle. These are AMOLED's inherent advantages over TFT.
LCD location;In addition, AMOLED features self-illumination and does not require a backlight.Therefore, it is thinner and thinner than TFT, andMore power-savingThere is also a more important feature, AMOLED without using the backlight can save
LCD 3 ~ The cost of a 4-proportion backlight module is flawed.Compared with other materials, the screen has a higher particle size at the same resolution.

 

Superamoled

Superamoled Full name: Super active matrix/Organic Light emittingdiode, in the original AMOLED screen with fast response, self-light, outstanding performance and lower power consumption advantages at the same time, the removal of glass covers provides better sunlight display. In addition, Super AMOLED is equipped with mdnie (mobile digital Natural Image Engine) technology to view and respond quickly from any angle. To put it simply,Super
AMOLED is an upgraded version of AMOLED.Available models: Samsung i9000 and Samsung S8500.

 

Superamoled plus

Super AMOLED plus (SAP), Chinese nickname: Magic screen, used to improve the Super AMOLED material,Improved previous super
AMOLED screen pentile pixel arrangement, the matrix is more normal, delicate. If calculated by pixel, the number of pixels on the new display will increase by 50%, both in contrast and outside readability compared to the previous super
The AMOLED screen has been improved.

The Super AMOLED, once proud of its predecessors, also features a great deal of scenery. However, in the later stage, it was said that it showed a large particle size and gradually became mediocre. The Super AMOLED plus panel was also launched by Samsung.

PS:

What is pentile?Arrange

Traditional pixels are composed of three sub-pixels: Red, green, and blue, while a single pixel of pentile is different. One is red-green, and the other is blue-green. We know that only three colors can constitute all colors, and the two colors cannot constitute all colors. Therefore, when an image is displayed, one pixel of A pentile will "borrow" another color of its adjacent pixel to form a three-base color. In the horizontal direction, each pixel and the adjacent pixel share the sub-pixel of the color that they do not have, and reach the white display together.To put it simply, pentile is a way to reduce the number of sub-pixels by sharing sub-pixels in adjacent pixels, so as to simulate High Resolution at low resolution.

 

Pentile Arrangement

The essence of pentile technology is to share sub-pixels of adjacent pixels.This requires that any pixel displayed on the screen must have an adjacent pixel, but in reality, this is not always possible! When you need to display fine content in actual applications,The essence of pentile will be exposed, and the definition will be greatly reduced, leading to the inability to clearly display the small fontIn order to make up for the color problem, when the pentile technology shows the color segmentation, the segmentation line will generate two times the actual pixel point distance, that is, it will generate a jagged edge. The last point is that as long as the displayed content is not white, there will be a grid-like spot that is twice the distance.

 

What is RGB arrangement?

RGB arrangement is the most standard arrangement. It divides a square-shaped Pixel into three equal points on average, and each part is given a different color so that a Color Pixel can be formed. This is also the sub-pixel arrangement method used by the vast majority of LCD monitors (of course, the order of the three pixels is random, not the country is generally "Red Green" or "blue green ").

The advantage of RGB arrangement is that pixels are highly independent, and each pixel can display all colors on its own. Super AMOLED plus technology changed the display arrangement to a more natural and delicate RGB mode.