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SD Library
Library for reading and writing from a Secure Digital (SD) card.
Source
Modified by Alvaro Lopes from the original Arduino source.
Soft Processor
Any ZPUino variant that has SPI on wishbone slot 6, such as the Hyperion variant.
Usage Notes
The SD card library uses the ZPUino SPI wishbone core to communicate with an SD card attached to the Papilio board. One of the benefits of using a Soft Processor on an FPGA is that we are able to move the SPI pins on the fly so we can connect an SD card programmatically to any of the Papilio pins. The example code located in the ZAP IDE shows how to move the SPI pins so we use either a microSD Wing or the microSD slot on the RetroCade Synth MegaWing.
This library can eat up quite a bit of space, if you only need read functionality then you can save 2KB of code space by disabling the write functionality. To disable write functionality edit your boards file in zap/hardware/zpuino/zpu/cores/zpuino/. Either edit board_papilio_one.h or board_papilio_pro.h depending on which hardware you have. Simply remove the "#define SD_WRITE_SUPPORT" line to save code space.
Reference from Arduino.cc
This section is directly from the SD Library section on Arduino.cc site which is covered by a Creative Commons Attribution-ShareAlike 3.0 License
SD Library
SD class
The SD class provides functions for accessing the SD card and manipulating its files and directories.
File class
The File class allows for reading from and writing to individual files on the SD card.