This is the Readme file to Objective Development's firmware-only USB driverfor Atmel AVR microcontrollers. For more information please visithttp://www.obdev.at/avrusb/This directory contains the USB firmware only. Copy it as-is to your ownproject and add your own version of "usbconfig.h". A template for your own"usbconfig.h" can be found in "usbconfig-prototype.h" in this directory.TECHNICAL DOCUMENTATION=======================The technical documentation (API) for the firmware driver is contained in thefile "usbdrv.h". Please read all of it carefully! Configuration options aredocumented in "usbconfig-prototype.h".The driver consists of the following files:  Readme.txt ............. The file you are currently reading.  Changelog.txt .......... Release notes for all versions of the driver.  usbdrv.h ............... Driver interface definitions and technical docs.* usbdrv.c ............... High level language part of the driver. Link this                           module to your code!* usbdrvasm.S ............ Assembler part of the driver. This module is mostly                           a stub and includes one of the usbdrvasm*.S files                           depending on processor clock. Link this module to                           your code!  usbdrvasm*.inc ......... Assembler routines for particular clock frequencies.                           Included by usbdrvasm.S, don't link it directly!  asmcommon.inc .......... Common assembler routines. Included by                           usbdrvasm*.inc, don't link it directly!  usbconfig-prototype.h .. Prototype for your own usbdrv.h file.* oddebug.c .............. Debug functions. Only used when DEBUG_LEVEL is                           defined to a value greater than 0. Link this module                           to your code!  oddebug.h .............. Interface definitions of the debug module.  iarcompat.h ............ Compatibility definitions for IAR C-compiler.  usbdrvasm.asm .......... Compatibility stub for IAR-C-compiler. Use this                           module instead of usbdrvasm.S when you assembler                           with IAR's tools.  License.txt ............ Open Source license for this driver.  CommercialLicense.txt .. Optional commercial license for this driver.  USBID-License.txt ...... Terms and conditions for using particular USB ID                           values for particular purposes.(*) ... These files should be linked to your project.CPU CORE CLOCK FREQUENCY========================We supply assembler modules for clock frequencies of 12 MHz, 15 MHz, 16 MHz and16.5 MHz. Other clock rates are not supported. The actual clock rate must beconfigured in usbdrv.h unless you use the default 12 MHz.12 MHz ClockThis is the traditional clock rate of AVR-USB because it's the lowest clockrate where the timing constraints of the USB spec can be met.15 MHz ClockSimilar to 12 MHz, but some NOPs inserted. On the other hand, the higher clockrate allows for some loops which make the resulting code size somewhat smallerthan the 12 MHz version.16 MHz ClockThis clock rate has been added for users of the Arduino board and otherready-made boards which come with a fixed 16 MHz crystal. It's also an optionif you need the slightly higher clock rate for performance reasons. Since16 MHz is not divisible by the USB low speed bit clock of 1.5 MHz, the codeis somewhat tricky and has to insert a leap cycle every third byte.16.5 MHz ClockThe assembler module for this clock rate differs from the other modules becauseit has been built for an RC oscillator with only 1% precision. The receivercode inserts leap cycles to compensate for clock deviations. 1% is also theprecision which can be achieved by calibrating the internal RC oscillator ofthe AVR. Please note that only AVRs with internal 64 MHz PLL oscillator can beused since the 8 MHz RC oscillator cannot be trimmed up to 16.5 MHz. Thisincludes the very popular ATTiny25, ATTiny45, ATTiny85 series as well as theATTiny26.We recommend that you obtain appropriate calibration values for 16.5 MHz coreclock at programming time and store it in flash or EEPROM or compute the valuefrom a reference clock at run time. Atmel's 8 MHz calibration is much moreprecise than the guaranteed 10% and it's therefore often possible to work witha fixed offset from this value, but it may be out of range.USB IDENTIFIERS===============Every USB device needs a vendor- and a product-identifier (VID and PID). VIDsare obtained from usb.org for a price of 1,500 USD. Once you have a VID, youcan assign PIDs at will.Since an entry level cost of 1,500 USD is too high for most small companiesand hobbyists, we provide a single VID/PID pair for free. If you want to useyour own VID and PID instead of our's, define the macros "USB_CFG_VENDOR_ID"and "USB_CFG_DEVICE_ID" accordingly in "usbconfig.h".To use our predefined VID/PID pair, you MUST conform to a couple ofrequirements. See the file "USBID-License.txt" for details.Objective Development also has some offerings which include product IDs. Seehttp://www.obdev.at/avrusb/ for details.HOST DRIVER===========You have received this driver together with an example device implementationand an example host driver. The host driver is based on libusb and compileson various Unix flavors (Linux, BSD, Mac OS X). It also compiles natively onWindows using MinGW (see www.mingw.org) and libusb-win32 (seelibusb-win32.sourceforge.net). The "Automator" project contains a nativeWindows host driver (not based on libusb) for Human Interface Devices.DEVELOPMENT SYSTEM==================This driver has been developed and optimized for the GNU compiler version 3(gcc 3). It does work well with gcc 4, but with bigger code size. We recommendthat you use the GNU compiler suite because it is freely available. AVR-USBhas also been ported to the IAR compiler and assembler. It has been testedwith IAR 4.10B/W32 and 4.12A/W32 on an ATmega8 with the "small" and "tiny"memory model. Not every release is tested with IAR CC and the driver maytherefore fail to compile with IAR. Please note that gcc is more efficient forusbdrv.c because this module has been deliberately optimized for gcc.USING AVR-USB FOR FREE======================The AVR firmware driver is published under the GNU General Public LicenseVersion 2 (GPL2). See the file "License.txt" for details.If you decide for the free GPL2, we STRONGLY ENCOURAGE you to do the followingthings IN ADDITION to the obligations from the GPL2:(1) Publish your entire project on a web site and drop us a note with the URL.Use the form at http://www.obdev.at/avrusb/feedback.html for your submission.(2) Adhere to minimum publication standards. Please include AT LEAST:    - a circuit diagram in PDF, PNG or GIF format    - full source code for the host software    - a Readme.txt file in ASCII format which describes the purpose of the      project and what can be found in which directories and which files    - a reference to http://www.obdev.at/avrusb/(3) If you improve the driver firmware itself, please give us a free licenseto your modifications for our commercial license offerings.COMMERCIAL LICENSES FOR AVR-USB===============================If you don't want to publish your source code under the terms of the GPL2,you can simply pay money for AVR-USB. As an additional benefit you getUSB PIDs for free, licensed exclusively to you. See the file"CommercialLicense.txt" for details.