AN1169 USB Mass Storage Class on an Embedded Device FEATURES Author: Sean Justice Microchip Technology Inc. This application note provides key components of an MSD device function driver. The Microchip MSD device function driver incorporates the following features: INTRODUCTION • Functions independently of RTOS or application In recent years, there has been immense growth in • Supports Microchip MPLAB IDE tool suite Universal Serial Bus (USB) based applications, • Supports the MSD 1.0 specification primarily due to the Plug-and-Play nature of USB. • Uses two USB endpoints that are configured for This application note discusses and provides a Mass bulk transfers Storage Device (MSD) function driver that can be inte- • File system support (FAT16, FAT32, NTFS) is grated with almost any application running on Micro- dependent on the host OS ® microcontroller products with USBchip 32-bit PIC • No custom drivers required peripheral support. It describes the design and imple- • Handles standard MSD USB configuration mentation of a USB MSD function driver using a requests, as stated in Chapter 9 of the “Universal Secure Digital card, which is useful to developers of Serial Bus Specification, Revision 2.0” (available USB mass storage solutions. on the Internet at the following URL: This application may be used as a stand-alone MSD or http://www.usb.org/developers/docs/ as a Secure Digital/Multimedia Card (SD/MMC) reader/ writer interface. The MSD function driver uses the LIMITATIONS Microchip PIC32 USB device stack. Since the MSD function driver is developed for use in embedded systems, the limitations are those that areASSUMPTIONS inherited by the USB device stack (refer to Microchip The author assumes that the reader is familiar with the Application Note AN1176, “USB Device Stack for ® IDEfollowing Microchip development tools: MPLAB PIC32 Programmer’s Guide”. and MPLAB REAL ICE™ in-circuit emulator. It is also assumed that the reader is familiar with C programming SYSTEM HARDWARE language, and USB device protocol and descriptors. Terminology from these technologies is used in this This application and firmware was developed for the document, and only brief overviews of the concepts are following hardware: provided. Advanced users are encouraged to read the • PIC32MX Family Microcontroller PIM (Processor associated specifications. Interface Module), supporting USB • Microchip Explorer 16 Development Board • USB PICtail™ Plus Daughter Board • PICtail™ Daughter Board for SD and MMC Cards The USB device and MSD function driver source files can be modified to use an alternative development board and accommodate most hardware differences.