The Graphic Display Controller (GDC) is a key engine at the heart of vehicle information and entertainment systems. These infotainment systems typically include head-end units that require a variety of human-machine interfaces and a full range of instruments. Graphic display controllers, which began to be designed for navigation systems in high-end vehicles on the Japanese and European markets, are now available in mid-range and low-end vehicles of various models around the world. It is also used in the entertainment system of vehicles.
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The vehicle GDC is a unique device that integrates many of the features required in a vehicle entertainment system. The basic function of the GDC is to control the LCD panel and produce a wide range of rich image content. GDC can implement advanced features such as navigation, characterization of analog meters, vibration splash screens, and other more vivid experiences without taking up too much resources on the main CPU. In addition, the GDC also performs power management, which makes it possible to dispense with some external cooling components such as fans or heat sinks.
Unlike desktop graphics controllers, GDCs for embedded applications are used for low-resolution small-screen applications. The resolution of a car display usually ranges from the CIF (320×240) used for basic information display to the Ultra Wide VGA (1024?480) used by the instrument. Due to the complex environment in the vehicle, a large amount of information needs to be displayed on these small screens, and the display is required to be clear, which brings some special challenges. The GDC uses multiple layers and multiple transparency to allow viewers to view several screens simultaneously. Similar to the Windows Workbench system, the screen size needs to be adjusted and moved to the display area. The GDC will allow viewing from below the screen or image to improve the display.
GDC performance classification
GDCs come in many different types and performance levels depending on the microcontroller used. Basically, there are 5 different performance levels.
The first type is the basic GDC, which includes a simple frame buffer memory and a controller that generates display signals. The main controller handles the drawing function and manually changes the display frame on the buffer. The second category is a more complex version that includes a frame buffer and a graphics engine with 2D capabilities, such as drawing lines and polygon graphics. This type of GDC will cover 2 or 3 layers and complete the alpha blending between the layers.
The third type of GDC covers more layers - possibly as many as 4 to 6 layers. This level of IC uses hardware sensors to implement alpha blending and alpha planes, and includes full-featured drawing capabilities.
The fourth type of GDC adds subordinate functions to the above functions: a 2D/3D graphics engine, a geometry processor, and a graphics engine with an internal working frequency of 100 to 200 MHz, which provides a high rendering rate. It can reach 400MHz when displaying the dot clock. The actual example is Fujitsu's 32-bit MB86296.
The last category is also the most advanced GDC, such as Fujitsu's MB86R01, another 32-bit IC that offers many additional multimedia features, including support for audio and video, and the ability to decode audio and video, not like other Types are just captures and adjustments. It also includes fogging, highlighting and programmable masking to provide a lively experience and a live feel, and the drawing rate is the fastest and highest of all graphic display controllers.
When selecting a GDC, it is also important to determine the amount of processing that will be sent to the CPU, if possible. If the main processor processing power can reach 400 MIPs or higher, there will be many cycles available, so it is possible to perform geometric operations with the CPU and perform bitmap operations with a simple GDC. On the other hand, if the main processor does not have a high enough processing speed, you must take advantage of the powerful GDC. The main processor must be fast enough to maintain bitmap coordinates and display lists for the GDC, so the relative level of the processor and GDC must be considered. Of course, the main considerations in the processor depend on the complexity of the displayed image or graphics.
Regardless of the IC, they are required to consume as little power as possible while performing the task. Many of the latest and most efficient controllers consume less than 2.3 watts of power, much less than previous power levels. Therefore, graphic display controllers are constantly improving their efficiency and performance.
Memory: key components in the GDC
Graphics memory is one of the most important components in the GDC system. In the GDC as a geometry and drawing engine that effectively performs drawing functions, the graphics memory provides a buffer, and all graphics information is stored here. Display frames on the display in the vehicle are also stored in the graphical display. This is very important for providing frame data to the video output interface in a timely and reliable manner. There are a range of different types of data stored in graphics memory, including drawing frames, display frames that are a subset of the drawing frames, Z-buffered data that carries the information needed for 3D drawing, and video capture buffered data from the video input interface (per pixel 16 bits), the polygon drawing flag buffer data (1 bit per pixel) required to draw a polygon, display list data, texture map, and Cursor Patterns data.
With such a large amount of information stored in graphics memory, memory accesses that extract information must be prioritized as follows:
Display frame refresh
2. Video capture
3. Display processing
4. Main CPU access (for displaying lists, texture maps and bitmaps)
5. Drawing access (Z-buffer, polygon flag buffer, etc.)
Display frame refresh updates the content on the display, 50 or 60 times per second. This work needs to transfer a large amount of data, which directly affects the effect of human-computer interaction. Therefore, it must be assigned the highest priority.
The second important thing mentioned above is video capture, which requires buffering the input video data in the graphics memory. The next one is display processing, including various processing related to the display controller, such as displaying alpha blending, overlay, pointer graph processing, and others. Next down is the main CPU access, which includes passing the display list, texture map, and bitmap to memory. The last one is a drawing access, which includes updating the drawing frame with a Z-buffer and a polygon flag buffer.
Since a large amount of data passes through the graphics memory interface, the bandwidth requirements for the interface are very high. The typical GDC's graphics memory bandwidth is 532MB/s. However, since memory reads and writes take multiple clock cycles, the actual effective bandwidth will only be 1/2 to 2/3 of this value, assuming a memory clock frequency of 133 MHz and a data bus width of 32 bits. The memory bandwidth of the high-end GDC is twice as high as this value, or close to 1GB/s. DDR-SDRAM technology can be used to increase the memory bandwidth of the highest-end GDC.
As shown in Figure 1, in addition to the memory interface, GDC also has a CPU interface, video capture interface and video output interface. Obviously, the vast majority of data passes through the memory interface. Display lists, bitmaps, and texture maps are transferred from the CPU to the GDC.
The CPU may also have to access the GDC register or memory directly. But all of these tasks don't generate a lot of data. For a PCI host interface (33MHz), the typical bandwidth of a GDC is 50MB/s. On the other hand, the SRAM type host interface bandwidth is higher than 100MB/s. This value depends on the bus clock frequency.
Figure 1: Block diagram of a typical GDC. In addition to the memory interface, GDC also has a CPU interface, video capture interface, and video output interface.
Similarly, the video capture and video output interfaces require less bandwidth than memory interfaces. These interfaces perform specialized tasks, with data flowing into the video capture interface and output from the video output interface. Therefore, the memory interface is the biggest bottleneck in the entire GDC system. Its architecture depends on the target application of GDC.
Dedicated memory architecture: optimal performance
According to the above, the memory interface must be dedicated. If you assign non-graphics to the memory, such as dialing a portion of it as the work area of ​​the main CPU, it will take up bandwidth and directly affect the performance of the GDC. In order to improve performance, this situation must be avoided. The solution, the solution adopted by Fujitsu GDC, isolates the CPU memory from the graphics processor.
The system requires separate memory for the GDC and a large PCB space to supply external components that do not provide graphics capabilities. Another solution is a unified memory architecture that allows the main CPU and GDC to share a single memory. If the system uses separate ICs for processing and graphics functions, the memory interface must be implemented with a CPU or GDC. For an IC without a memory interface, the memory data stream must be transmitted by connecting it to the interface of another IC.
Figure 2: Comparison of external and internal CPU-GDC communications.
A better way to implement this architecture is to use a high-speed data channel in the SOC to simultaneously integrate the main CPU and GDC onto a single chip to achieve high-bandwidth CPU-GDC communication. This interface is easier to implement on-chip than on the outside, and can meet both bandwidth requirements and space constraints without sacrificing GDC performance. With today's processing technology, it is possible to develop such an SOC at a reasonable cost.
Today, GDC's rich variety and performance enable a range of innovative infotainment applications in vehicles around the world. They are a key component in navigation and video products, and as automakers differentiate their models and types, they will become even more important.
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