Wireless endoscopy system solution using ARM and CPLD

At present, medical wireless endoscope products have been launched. At present, there is no independent manufacturing capability of this product in China, and foreign products are expensive. Therefore, it is of great significance to develop wireless endoscope products with independent intellectual property rights. This paper introduces the system structure of wireless endoscope system, the implementation of image compression standard JPEG-LS on ARM7 platform, and the debugging and optimization methods used in the implementation process.

1. System composition and working principle

1. Composition and structure of endoscopy system

As shown in Figure 1, the wireless endoscope system mainly consists of a host and a slave (wireless endoscope). The slave collects the original image through the camera, compresses it, and transmits the compressed image data to the host wirelessly; the host receives the compressed image through a USB connection to the Bluetooth adapter and forwards it to the management software on the PC, which decompresses the image and displays it.

Figure 1 Endoscopic system structure diagram

2. Composition and structure of wireless endoscope

As shown in Figure 2, the wireless endoscope uses the CPLD chip EPM7256-144 to realize the image acquisition control of the 300,000-pixel CMOS camera OV7660, as well as the switching of the data and address buses. Using Atmel's ARM7 chip AT91R40008, JPEG-LS lossless image compression and Bluetooth wireless data transmission are realized, and temperature and pressure acquisition, controllable light source and system control are realized. The image data exchange between CPLD and ARM7 is realized through the 8-bit data bus, and the handshake control between ARM7 and CPLD is realized through the I/O port line. Due to the large amount of image data, it is calculated to be hundreds of thousands of bytes according to the 640×480 resolution and 8-bit image format, so this system has expanded 2 512KB SRAMs on the external chip in ping-pong mode as data cache. [page]

Figure 2: Wireless endoscope hardware structure diagram

3. System working principle

The endoscopy system can realize continuous image acquisition and control of temperature, humidity, lighting brightness, etc. Image acquisition is the core of the system, and its workflow is as follows:

①By default, the system works in sleep mode.

② The staff sends a command through the PC management software to start collecting images. The software sends the command to the Bluetooth adapter through the USB interface and then to the wireless endoscope.

③After the endoscope receives the image acquisition command, ARM controls the CPLD to start collecting image data.

④CPLD writes the collected image data into a SRAM, switches the ARM bus to the SRAM, and notifies ARM to perform compression; at the same time, CPLD continues to collect the next frame of image into another SRAM, so as to improve the system throughput.

⑤ARM returns the response command through the Bluetooth module and returns the header information of the collected JPEG-LS image.

⑥ The PC management software sends a command to receive the next line of compressed image. ARM compresses the original image of this line and sends the compressed data. If an error occurs, it can be resent. Repeat this step to obtain the entire frame of compressed image.

⑦ PC software decodes and displays the compressed images, and provides other additional functions such as image processing and saving.

⑧Repeat steps ②~⑦ to obtain the next frame of compressed image.

From the above process, it can be seen that JPEG-LS compression and wireless channel transmission determine the image transmission rate of the entire system. Wireless transmission uses Bluetooth technology, and its nominal air rate is 1 Mbps, which is not easy to improve; therefore, the core of the system design is the coding efficiency of JPEG-LS.