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This is the Readme file to Objective Development's firmware-only USB driver

for Atmel AVR microcontrollers. For more information please visit

http://www.obdev.at/vusb/

This directory contains the USB firmware only. Copy it as-is to your own

project and add all .c and .S files to your project (these files are marked

with an asterisk in the list below). Then copy usbconfig-prototype.h as

usbconfig.h to your project and edit it according to your configuration.

TECHNICAL DOCUMENTATION

=======================

The technical documentation (API) for the firmware driver is contained in the

file "usbdrv.h". Please read all of it carefully! Configuration options are

documented 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.

  usbportability.h ....... Header with compiler-dependent stuff.

  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.

  USB-ID-FAQ.txt ......... General infos about USB Product- and Vendor-IDs.

  USB-IDs-for-free.txt ... List and terms of use for free shared PIDs.

(*) ... These files should be linked to your project.

CPU CORE CLOCK FREQUENCY

========================

We supply assembler modules for clock frequencies of 12 MHz, 12.8 MHz, 15 MHz,

16 MHz, 16.5 MHz 18 MHz and 20 MHz. Other clock rates are not supported. The

actual clock rate must be configured in usbconfig.h.

12 MHz Clock

This is the traditional clock rate of V-USB because it's the lowest clock

rate where the timing constraints of the USB spec can be met.

15 MHz Clock

Similar to 12 MHz, but some NOPs inserted. On the other hand, the higher clock

rate allows for some loops which make the resulting code size somewhat smaller

than the 12 MHz version.

16 MHz Clock

This clock rate has been added for users of the Arduino board and other

ready-made boards which come with a fixed 16 MHz crystal. It's also an option

if you need the slightly higher clock rate for performance reasons. Since

16 MHz is not divisible by the USB low speed bit clock of 1.5 MHz, the code

is somewhat tricky and has to insert a leap cycle every third byte.

12.8 MHz and 16.5 MHz Clock

The assembler modules for these clock rates differ from the other modules

because they have been built for an RC oscillator with only 1% precision. The

receiver code inserts leap cycles to compensate for clock deviations. 1% is

also the precision which can be achieved by calibrating the internal RC

oscillator of the AVR. Please note that only AVRs with internal 64 MHz PLL

oscillator can reach 16.5 MHz with the RC oscillator. This includes the very

popular ATTiny25, ATTiny45, ATTiny85 series as well as the ATTiny26. Almost

all AVRs can reach 12.8 MHz, although this is outside the specified range.

See the EasyLogger example at http://www.obdev.at/vusb/easylogger.html for

code which calibrates the RC oscillator based on the USB frame clock.

18 MHz Clock

This module is closer to the USB specification because it performs an on the

fly CRC check for incoming packets. Packets with invalid checksum are

discarded as required by the spec. If you also implement checks for data

PID toggling on application level (see option USB_CFG_CHECK_DATA_TOGGLING

in usbconfig.h for more info), this ensures data integrity. Due to the CRC

tables and alignment requirements, this code is bigger than modules for other

clock rates. To activate this module, you must define USB_CFG_CHECK_CRC to 1

and USB_CFG_CLOCK_KHZ to 18000 in usbconfig.h.

20 MHz Clock

This module is for people who won't do it with less than the maximum. Since

20 MHz is not divisible by the USB low speed bit clock of 1.5 MHz, the code

uses similar tricks as the 16 MHz module to insert leap cycles.

USB IDENTIFIERS

===============

Every USB device needs a vendor- and a product-identifier (VID and PID). VIDs

are obtained from usb.org for a price of 1,500 USD. Once you have a VID, you

can assign PIDs at will.

Since an entry level cost of 1,500 USD is too high for most small companies

and hobbyists, we provide some VID/PID pairs for free. See the file

USB-IDs-for-free.txt for details.

Objective Development also has some license offerings which include product

IDs. See http://www.obdev.at/vusb/ for details.

DEVELOPMENT SYSTEM

==================

This driver has been developed and optimized for the GNU compiler version 3

and 4. We recommend that you use the GNU compiler suite because it is freely

available. V-USB has also been ported to the IAR compiler and assembler. It

has been tested with 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 may therefore fail to compile with IAR. Please note that gcc is

more efficient for usbdrv.c because this module has been deliberately

optimized for gcc.

Gcc version 3 produces smaller code than version 4 due to new optimizing

capabilities which don't always improve things on 8 bit CPUs. The code size

generated by gcc 4 can be reduced with the compiler options

-fno-move-loop-invariants, -fno-tree-scev-cprop and

-fno-inline-small-functions in addition to -Os. On devices with more than

8k of flash memory, we also recommend the linker option --relax (written as

-Wl,--relax for gcc) to convert absolute calls into relative where possible.

For more information about optimizing options see:

    http://www.tty1.net/blog/2008-04-29-avr-gcc-optimisations_en.html

These optimizations are good for gcc 4.x. Version 3.x of gcc does not support

most of these options and produces good code anyway.

USING V-USB FOR FREE

====================

The AVR firmware driver is published under the GNU General Public License

Version 2 (GPL2) and the GNU General Public License Version 3 (GPL3). It is

your choice whether you apply the terms of version 2 or version 3.

If you decide for the free GPL2 or GPL3, we STRONGLY ENCOURAGE you to do the

following things IN ADDITION to the obligations from the GPL:

(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/vusb/feedback.html for your submission.

If you don't have a web site, you can publish the project in obdev's

documentation wiki at

http://www.obdev.at/goto.php?t=vusb-wiki&p=hosted-projects.

(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/vusb/

(3) If you improve the driver firmware itself, please give us a free license

to your modifications for our commercial license offerings.

COMMERCIAL LICENSES FOR V-USB

=============================

If you don't want to publish your source code under the terms of the GPL,

you can simply pay money for V-USB. As an additional benefit you get

USB PIDs for free, reserved exclusively to you. See the file

"CommercialLicense.txt" for details.