Abstract: This paper introduces the VBE standard developed by the Video Electronics Standards Association (VESA). In combination with the standard, the three software implementation schemes of real-time rolling display system based on embedded platform for remote sensing images are compared, which highlights the hardware of the standard. The advantages of resource occupation. Finally, this paper presents an implementation scheme of real-time dynamic display system for remote sensing images based on embedded computer platform and VBE standard.
Keywords: VGA standard: VBE standard: dynamic image real-time display
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0 Introduction The open architecture of PCs allows more vendors to participate in the production of computer components and participate in the development of standards. In the early days of PC graphics display, IBM's VGA standard became the default industry standard, but for a while, other manufacturers' VGA graphics cards were compatible with the IBM VGA BIOS and registers, but added extensions. There have been many display cards with higher resolution, more colors and even additional graphics processing - Super VGA graphics card.
At the time, software developers for Super VGA cards faced a very serious problem: because there were no hardware design standards, software developers faced a variety of completely different Super VGA hardware structures, and because there was no A unified software development interface, in the development of the program must solve the problem of software compatible with different display cards, and then, for a specific Super VGA display card, in addition to some specific software can get the display driver provided by the manufacturer With program support, there are almost no software packages that take advantage of the power and benefits of Super VGA.
The development of the VBE standard is to change this dilemma. As a unified software interface for various Super VGA graphics cards, it can make application software and system software take advantage of the extended VGA available to a large extent.
This paper first introduces the VBE standard briefly, and then combines a specific design to give a real-time scrolling display of remote sensing images using the VBE standard.
1 VBE standard VBEl. 0 provides several basic functions such as basic information query, display mode information query, setting display mode, returning current display mode, saving/restoring video state, and defining a limited number of extended display modes.
VBEl. 1 Added the ability to set/get the length of the logical scan line, and added 5 display modes and new display mode parameters.
VBEl. 2 Added the interface set for the palette and more display modes and display mode parameters.
VBE 2.0 adds support for linear frame buffering and protection modes.
VBE 3.0 expands many of the features in previous versions, enabling refresh rates, dot clocks, hardware frame switching, and more. Due to space limitations, only the software interface defined by the VBE-2.0 standard widely supported by hardware vendors is briefly introduced here.
The standard VGA BIOS is invoked by interrupting lO, while VBE calls the different functions of the standard by setting a different function number by interrupting 4F:
(1) Function call 00H--Basic information query It can return VBE version number, OEM name, display video environment capability, supported display mode, display memory number and other information.
(2) Function call 01H--Display mode information query can return specific information of specific display mode, including display mode attribute, host video window attribute, function call entry address, resolution, pixel number, display memory block number, minute Block length, etc.
(3) Function call 02H--Set display mode Set the display mode.
(4) Function call 03H--Return display mode Returns the current display mode.
(5) Function call 04H--Save/Restore Video Status Save/Restore Video Status.
(6) Function call 05H--Host video window control Set the position of the host video window in the display memory.
(7) Function call 06H--Set/get the length of the logical scan line Set or obtain the length of the logical scan line by controlling the sub-function.
(8) Function call 07H--Set/Get display start address Set or get the display start address by controlling the sub function.
(9) Function call 08H--Set/Get palette format Implement the settings or get the palette format by controlling the sub-functions.
(10) Function call 09H--Set/Get palette data Set or acquire palette data by controlling the sub-functions.
(11) Function call 0AH--Return to protected mode interface Return to protected mode program interface.
2 Remote sensing image real-time scrolling display system design requirements Remote sensing image real-time scrolling display system has the following characteristics:
(1) The image size is large, and the number of rows of pixels is large;
(2) Image scrolling display, fast speed, more refresh lines per second;
(3) The display information is rich, in addition to displaying the dynamic image, it is also necessary to superimpose and display the text information and the grid information on the image;
(4) There is a good visual effect, and the image scrolling display cannot have a feeling of jumping;
(5) Based on embedded platform that can meet special environmental requirements.
Based on the above design constraints, the display speed requirement of the dynamic image real-time display system is relatively high. The specific technical indicators are as follows:
Input data rate: ≤2.5Mb/s
Enter the number of pixels per line: 8192 points / line Input data format: Remote sensing image + auxiliary data Display word length: 8bit
Display image gray level: 256
Screen display mode: Scroll display Mesh ruler overlay display: Hotkey selection Auxiliary information character display: Hotkey selection Image display mode: A. High-resolution partial display, line display start optional B. Sampling global display, row to 8 pumping 1, column to 8 pumping 1
The real-time display system is required to superimpose the displayed auxiliary data characters and the grid scale at a fixed position while scrolling the display image in the 1024×768 display mode. Due to the need to superimpose both scrolling and still images in the full screen range, it is difficult to implement on the embedded platform.
3 Comparison of several software implementation schemes According to the performance of the embedded computer's display card and the available programming software library, the following three methods can be used to realize the real-time image display software:
(1) Frame-switching based on frame switching-based scrolling image and still image overlay display is realized by a similar movie projection method, that is, a full-screen image constitutes one frame, and many such frames together constitute a frame sequence, which is sequentially displayed on the screen. These sequence of frames form a superimposed static grid and text while the image is scrolling.
According to the requirements of the real-time display, when the frame switching method constitutes one frame, the image data of the entire frame is first reconstructed in the background video memory, and then the grid and the text are written to the corresponding address of the video memory. The data transfer amount of this method is very large, the required display memory capacity is large, and the access speed of the video memory is high.
(2) Based on frame switching, and using hardware two-dimensional acceleration function to realize frame switching by hardware two-dimensional acceleration function, this method is similar to the above method, except that it takes advantage of hardware, that is, scrolling displayed image and still The grid and the text are respectively stored in different areas of the display memory, and are superimposed by the hardware of the display card at the time of display, so that the operation of each frame image is basically concentrated only in the storage area of ​​the image data.
At this time, the main task of constructing one frame is to reconstruct the image data of the entire frame. Since the grid and the text are stored in another address space in the video memory, in general, only the individual characters need to be operated. However, the data transfer amount of this method is still very large, the system memory addressability requirement is high, and the required display memory capacity is larger.
(3) Based on changing the start address of the display window in the video memory In the display memory, only a small portion of the video memory is displayed on the screen. When the display mode is set, the entire display memory can be regarded as a long-length picture, and the display only shows a part of it as a window. We can change the content of the screen by changing the starting address of the display window in memory. If the change is sequential and continuous, a scrolling image will be formed on the screen.
Each time the input image data is stored in the memory, and then the required processing (such as adding a vertical grid line), when the screen scrolling is required, first change the starting address of the display window in the memory, and then process the horizontal Grid lines and text so they are in the right position on the screen. The data transfer amount of this method is relatively small, and the required system memory and display memory capacity are also small, but the data processing of this method is complicated, and various boundary effects need to be considered in the programming process. At the same time, when the user does not need to display grid lines and text, the processing amount of recovering the original image data that has been destroyed by the displayed grid lines and characters is very large, and whether it is possible to realize the system memory and the display memory depending on the target system. Access speed and efficiency of the programming language.
Combined with the real-time display of the technical indicators of the extension, the advantages and problems of each of the above three methods can be specified by Table 1:
For the ordinary computer platform, the three implementation methods can meet the requirements of the system, but in the actual engineering implementation, the environmental factors should be considered to limit the structure, temperature and humidity of the target system. When the target system that is limited can meet the requirements, it becomes a key factor that restricts the image display scheme.
Considering the special environmental adaptability requirements, the embedded computer of the dynamic image real-time display system must have a pin-type mechanical structure, and at the same time have a small volume and have various PCI interfaces. Therefore, considering the cost and volume constraints, the embedded computer of the PC104plus structure is selected. The display memory of such a computer is rarely configured at 2M or more. Therefore, the frame switching method using the hardware two-dimensional acceleration function cannot be applied temporarily. Although the PC104plus computer can obtain 2M memory, but because the system frequency is low, the system memory and display memory speed are slow. After testing, the frame switching method can only achieve the display speed of 25frame/s, considering the time taken by the image data input. At most, it can only guarantee 15frame/s. This update speed will cause the image to flicker and is unacceptable.
4 VBE-based image real-time display software solution The method based on changing the starting address of the display window in memory can be realized through the VBE programming interface, as follows:
4.1 Target system In the target system, the part related to the image display output is the embedded computer and the display card integrated on it. The embedded computer is a PC104plus structure with PCI and ISA bus interfaces, and its CPU is Pentium. MMXl66, system memory 32M, display control chip is M69000, display memory 2M.
4.2 Image real-time display software The image real-time display software consists of three modules: data read-in, display output and display control. The following only shows the relevant display output modules.
The display output module is configured to scroll display image data in a high resolution display mode of 1024×768, while superimposing and displaying fixed auxiliary data characters and grids, and the operator can control whether to display auxiliary data characters and grids through the display control module. . Each time the image is scrolled, the display output module needs to do the following:
(1) Change the current read and write window;
(2) writing the read data to the corresponding address of the video memory;
(3) writing longitudinal grid lines;
(4) Restoring the image data on the original horizontal grid line (the current read/write window needs to be changed during this period);
(5) Write a new horizontal grid line:
(6) restoring image data on the original auxiliary data characters;
(7) writing new auxiliary data characters;
(8) change the starting address of the display window in the video memory to make the screen scroll;
(9) Repeat (1)
4.3 Performance Tests show that each time you scroll 2 lines, you can scroll 120 lines per second. If you scroll 4 lines at a time, you can reach 240 lines per second. In both cases, there is no obvious jump when the image is scrolled. Dynamic.
5 Summary With the development of computer technology, the VBE standard is constantly being upgraded, and the highest version is version 3.0. At the same time, some sub-standards are also derived, such as VBE/AF, VBE/AI, VBE/PM, etc. However, the mainstream of computer display systems is developing in the direction of three-dimensional acceleration and stereoscopic display. Many of these mainstream development directions are not supported by VBE. However, in some special application areas, the VBE standard is still a good solution for a dynamic image real-time display system that adapts to high environmental requirements.
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