103 lines
4.5 KiB
Plaintext
103 lines
4.5 KiB
Plaintext
This is the Readme file for the directory "examples" of V-USB, a firmware-
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only USB driver for AVR microcontrollers.
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WHAT IS IN THIS DIRECTORY?
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==========================
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This directory contains examples which are mostly for educational purposes.
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Examples can be device firmware only, host software only or both. Here is
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a summary:
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custom-class
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A custom class device with host software based on libusb. It demonstrates
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the straight forward way of sending small amounts of data to a device and
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receiving data from the device. It does NOT demonstrate how to send large
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amounts of data to the device or how to receive data generated on the fly
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by the device (how to use usbFunctionWrite() and usbFunctionRead()). See
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the hid-data example for how usbFunctionWrite() and usbFunctionRead() are
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used.
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hid-custom-rq
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This example implements the same functionality as the custom-class example
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above, but declares the device as HID. This prevents the "give me a driver
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CD" dialog on Windows. The device can still be controlled with libusb as in
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the previous example (on Windows, the filter version of libusb-win32 must
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be installed). In addition to the features presented in custom-class, this
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example demonstrates how a HID class device is defined.
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hid-mouse
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This example implements a mouse device. No host driver is required since
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today's operating systems have drivers for USB mice built-in. It
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demonstrates how a real-world HID class device is implemented and how
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interrupt-in endpoints are used.
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hid-data
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This example demonstrates how the HID class can be misused to transfer
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arbitrary data over HID feature reports. This technique is of great value
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on Windows because no driver DLLs are needed (the hid-custom-rq example
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still requires the libusb-win32 DLL, although it may be in the program's
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directory). The host side application requires no installation, it can
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even be started directly from a CD. This example also demonstrates how
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to transfer data using usbFunctionWrite() and usbFunctionRead().
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usbtool
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This is a general purpose development and debugging tool for USB devices.
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You can use it during development of your device to test various requests
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without special test programs. But it is also an example how all the
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libusb API functions are used.
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More information about each example can be found in the Readme file in the
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respective directory.
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Hardware dependencies of AVR code has been kept at a minimum. All examples
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should work on any AVR chip which has enough resources to run the driver.
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Makefile and usbconfig.h have been configured for the metaboard hardware (see
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http://www.obdev.at/goto.php?t=metaboard for details). Edit the target
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device, fuse values, clock rate and programmer in Makefile and the I/O pins
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dedicated to USB in usbconfig.h.
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WHAT IS NOT DEMONSTRATED IN THESE EXAMPLES?
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===========================================
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These examples show only the most basic functionality. More elaborate
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examples and real world applications showing more features of the driver are
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available at http://www.obdev.at/vusb/projects.html. Most of these
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features are described in our documentation wiki at
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http://www.obdev.at/goto.php?t=vusb-wiki.
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To mention just a few:
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Using RC oscillator for system clock
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The 12.8 MHz and 16.5 MHz modules of V-USB have been designed to cope
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with clock rate deviations up to 1%. This allows an RC oscillator to be
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used. Since the AVR's RC oscillator has a factory precision of only 10%,
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it must be calibrated to an external reference. The EasyLogger example
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shows how this can be done.
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Dynamically generated descriptors
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Sometimes you want to implement different typtes of USB device depending
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on a jumper or other condition. V-USB has a very flexible interface for
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providing USB descriptors. See AVR-Doper for how to provide descriptors
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at runtime.
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Virtual COM port
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Some people prefer a virtual serial interface to communicate with their
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device. We strongly discourage this method because it does things
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forbidden by the USB specification. If you still want to go this route,
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see AVR-CDC.
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Implementing suspend mode
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V-USB does not implement suspend mode. This means that the device does
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not reduce power consumption when the host goes into sleep mode. Device
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firmware is free to implement suspend mode, though. See USB2LPT for an
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example.
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The projects mentioned above can best be found on
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http://www.obdev.at/vusb/prjall.html
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where all projects are listed.
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----------------------------------------------------------------------------
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(c) 2009 by OBJECTIVE DEVELOPMENT Software GmbH.
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http://www.obdev.at/
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