Jpeg Image Process For Transmission By USB Interface

The design of the system module involved in this article is based on the AT91SAM9263 platform. It is required that within one second the image captured should be encoded with JPEG and transmitted to the host through the USB 2.0 interface.In the actual process of designing, we have to simulate the SCCB, which is a private protocol, to configure OV9650 with AT91SAM9263 general input/output pins, which provides the Image Sensor Interface to connect CMOS image sensor.The bulky image data captured with OV9650 is in RGB565 format, which should be encoded with JPEG into proper size for transmission.The module migrates the JPEG standard library to AT91SAM9263 and largely adopts the float calculation for Discrete Cosine Transform in JPEG encoder. Because no float coprocessor is integrated into the MPU, and the efficiency would be lower if using the IAR complier system to optimize the float calculation, the article makes full use of other optimal methods based on the ARM platform, like the fixed point data instead of the float data, the shift-addition/ subtraction replaced the multiply. In one word, the best way to speed up the operation speed system is to use the 32bit integer capacity of ARM kernel.When designing the USB firmware, the ATMEL protocol library is made use of for the purpose of communicating and controlling.Largely owing to the various optimization mentioned above, the executive efficiency of the JPEG encoder module, which consumes the largest chunk of the resources of the MPU, is improved by 90%, shrinking the system's image capturing time to a standard level as required by the design documents.