The domestic Loongson 1A handheld computer and ReWorks embedded operating system provide a unified interface for the upper layer application by transplanting the touch middleware tslib, which realizes the calibration and testing of the touch screen.
1, review
The Loongson series processor is a general-purpose CPU independently developed by China. The Loongson 1 series processor is suitable for embedded applications such as industrial control and consumer electronics (mobile phones/MP4/PDAs). The Loongson 1A chip integrates 32-bit processor core, 2D GPU, VGA and LCD display interfaces, and Southbridge chipset functions to meet ultra-low-cost cloud terminals, industrial control/data acquisition, network equipment, and consumer electronics. And other field needs.
The ReWorks embedded operating system is an embedded real-time operating system developed by the China Electronics Technology Group based on the technical achievements of the “Ninth Five-Year Plan†and the “Tenth Five-Year Plan†and has all the source code. It is suitable for a variety of target hardware environments (x86, mips). .
In embedded, especially handheld electronic devices, the touch screen has gradually replaced the physical keyboard as the mainstream input device of the embedded computer system because of its friendly human-computer interaction, convenient and flexible operation, fast input speed and small space occupation.
At present, the debugging method of the touch screen under the general operating system such as Windows or Linux is mature, but there is no research on the touch screen debugging method of the domestic embedded operating system ReWorks. This paper introduces the handheld computer based on the domestic Godson 1A processor as the hardware platform. Calibration and testing of the touch screen under the domestic embedded operating system ReWorks.
2, touch screen calibration principle
In practical applications, the touch screen is generally used as an input device for use with a liquid crystal screen, and the coordinates obtained by sampling the touch screen need to be mapped with the display coordinates of the liquid crystal screen, that is, the so-called touch screen calibration. The purpose is to calculate the calibration coefficient by reading the coordinate values ​​of several points, save the calculated coefficients, and then click the touch screen coordinates obtained by the touch screen every time, and then pass the calibration coefficient to obtain the coincidence on the LCD screen. coordinate.
In this paper, the handheld computer uses a four-wire resistive touch screen, the touch screen controller uses the ADS7843E, and the touch screen calibration library tslib uses a five-point calibration. The touch screen control principle is shown in Figure 2.
Figure 2 touch screen control schematic
3, ReWorks calibration and test touch screen implementation
Tslib is a touch screen support library that provides a unified interface for different touch screens, as well as features such as filtering, debounce, and calibration. Tslib obtains raw device coordinate data from the touch screen driver, and removes noise and converts the original device coordinates into corresponding screen coordinates through a series of operations such as denoising, debounce, and coordinate transformation. This article transplants tslib to the domestic ReWorks operating system + Godson 1A processor (mips) platform, which realizes the calibration and testing functions of the touch screen under ReWorks. The tslib hierarchy under ReWorks system is shown in Figure 3.
Figure 3 tslib hierarchy diagram under ReWorks system
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