Design And Implementation Of The Process For Opening Secure Digital Card

SD card (Secure Digital memory card) is widely used in every kind of consumer electronic devices, such as digital cameras, mobile phones and video players etc. The demands for SD card will increase rapidly. The research of opening card is an essential and very important part for designing SD card. It relates to whether SD card can be mass production successfully. So it has great benefit in economics to design and implement an efficient and flexible method for opening card.After more than 20 years of development, NANDFlash has been mainstream storage media. Because of restrictions on technology, NandFlash has bad blocks inevitably. In addition, in order to reduce waste and costs, recycling flash chip usually be reused for SD card. The recycling flash has more bad blocks, so it's critical to manage bad blocks effectively.This article proposed a novel method for opening card based on ZD5820 chip, which was designed by Beijing embedded system key laboratory. The goal is compatibility, efficiency, reliability and flexibility. This article will study:(1) System parameters are designed to shield the difference of flash structure through analyzing every kind of flash and the management algorithm. So the chip has good compatibility for different flashes. In addition, an algorithm of checking flash structure quickly based on ZD5820 chip is proposed and implemented in order to handle different flashes and improve the efficiency of opening card.(2) In order to assure the efficiency, a new method of detecting bad block, which combines software and hardware, is proposed through researching the general method. And then, this article proposed a new bad block management algorithm based on Zone and bad block table. This algorithm not only greatly reduces the demand for RAM space, but also ensures the reliability of SD card.(3) This article designs the communication protocol of CMD56 which is the general read-write command based on the security and functional requirements. Then designs and implements the scheme for updating driver dynamically to ensure the flexibility of opening card.(4) A scheme for loading file system based on FAT is proposed to help customers use SD card conveniently. In addition, this article improves the design of opening card for the recycling flash and reduces the cost.The experiment results show that this scheme for opening card can be used on ZD5820-based SD card successfully; ZD5820 has been used in mass production, so this scheme is of high value in business.