The Implementation And Optimization Of Hard Disk Data Transfer Based On Embedded WINDOWS CE.NET System

As embedded devices increase in functionality, greater in-system storage capacity is needed. At the same time, hard-disk drives, subsequently referred to as HDDs, are increasing in capacity while decreasing in price and size. Small HDDs have become competitive to flash storage for some designs. Potential uses of these small HDDs include MP3 players, portable media player, portable gaming systems, PDAs, GPS navigation devices and etc.The implementation and optimization of Hard-disk data transfer described in this paper is based on a PDA's platform, which uses PXA255 processor as its core processor. The Intel PXA255 Processor offers an integrated system-on-a-chip design based on the Intel XScale microarchitecture. The PXA255 processor memory controller provides several possible solutions to implement an HDD interface. These interfaces include the PCMCIA/ Compact Flash interface and the variable latency input/output (VLIO) interface.The CPLD is used to connect the HDD to the VLIO interface of Intel processor in the design. Configurations using programmed IO (PIO) and flow-through DMA are presented. The VLIO interface solution only requires a small number of additional components and produces low-cost and efficient DMA performance. The design discussed is designed to work under PIO mode 4 and DMA mode 2, but not Ultra DMA or any other working mode.The HDD driver, which is registered to the OS as a block device driver for Microsoft Windows CE.net, is designed using stream interface. The read/write and IOCTL operations are implemented in the driver. Both PIO mode and DMA mode are supported in the driver with the same read/write interface to upper layer applications. In order to reduce the occupation rate of the cpu, interrupt mode is used to control the data transfer of the hard disk. Besides, as the battery in the embedded system is limited and the power consumption of hard disk is high, a simple power management strategy is presented to reduce the system power consumption. At last, the driver is optimized to improve the data transfer rate and the driver is tested.Till now, all the work described in this paper is completed. The HDD driver has been tested by CETK and runs well in the PDA system. Test results reveal that data transfer rate is about 2.2～2.3MB/s in PIO mode and 2.4～2.5MB/s in DMA mode.