173 lines
8.3 KiB
Plaintext
173 lines
8.3 KiB
Plaintext
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This is the readme file to Objective Development's firmware-only USB driver
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for Atmel AVR microcontrollers. For more information please visit
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http://www.obdev.at/vusb/
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This directory contains the USB firmware only. Copy it as-is to your own
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project and add all .c and .S files to your project (these files are marked
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with an asterisk in the list below). Then copy usbconfig-prototype.h as
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usbconfig.h to your project and edit it according to your configuration.
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TECHNICAL DOCUMENTATION
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=======================
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The technical documentation (API) for the firmware driver is contained in the
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file "usbdrv.h". Please read all of it carefully! Configuration options are
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documented in "usbconfig-prototype.h".
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The driver consists of the following files:
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readme.txt ............. The file you are currently reading.
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Changelog.txt .......... Release notes for all versions of the driver.
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usbdrv.h ............... Driver interface definitions and technical docs.
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* usbdrv.c ............... High level language part of the driver. Link this
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module to your code!
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* usbdrvasm.S ............ Assembler part of the driver. This module is mostly
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a stub and includes one of the usbdrvasm*.S files
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depending on processor clock. Link this module to
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your code!
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usbdrvasm*.inc ......... Assembler routines for particular clock frequencies.
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Included by usbdrvasm.S, don't link it directly!
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asmcommon.inc .......... Common assembler routines. Included by
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usbdrvasm*.inc, don't link it directly!
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usbconfig-prototype.h .. Prototype for your own usbdrv.h file.
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* oddebug.c .............. Debug functions. Only used when DEBUG_LEVEL is
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defined to a value greater than 0. Link this module
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to your code!
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oddebug.h .............. Interface definitions of the debug module.
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usbportability.h ....... Header with compiler-dependent stuff.
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usbdrvasm.asm .......... Compatibility stub for IAR-C-compiler. Use this
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module instead of usbdrvasm.S when you assembler
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with IAR's tools.
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License.txt ............ Open Source license for this driver.
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CommercialLicense.txt .. Optional commercial license for this driver.
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USB-ID-FAQ.txt ......... General infos about USB Product- and Vendor-IDs.
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USB-IDs-for-free.txt ... List and terms of use for free shared PIDs.
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(*) ... These files should be linked to your project.
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CPU CORE CLOCK FREQUENCY
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========================
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We supply assembler modules for clock frequencies of 12 MHz, 12.8 MHz, 15 MHz,
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16 MHz, 16.5 MHz 18 MHz and 20 MHz. Other clock rates are not supported. The
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actual clock rate must be configured in usbconfig.h.
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12 MHz Clock
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This is the traditional clock rate of V-USB because it's the lowest clock
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rate where the timing constraints of the USB spec can be met.
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15 MHz Clock
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Similar to 12 MHz, but some NOPs inserted. On the other hand, the higher clock
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rate allows for some loops which make the resulting code size somewhat smaller
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than the 12 MHz version.
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16 MHz Clock
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This clock rate has been added for users of the Arduino board and other
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ready-made boards which come with a fixed 16 MHz crystal. It's also an option
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if you need the slightly higher clock rate for performance reasons. Since
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16 MHz is not divisible by the USB low speed bit clock of 1.5 MHz, the code
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is somewhat tricky and has to insert a leap cycle every third byte.
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12.8 MHz and 16.5 MHz Clock
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The assembler modules for these clock rates differ from the other modules
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because they have been built for an RC oscillator with only 1% precision. The
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receiver code inserts leap cycles to compensate for clock deviations. 1% is
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also the precision which can be achieved by calibrating the internal RC
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oscillator of the AVR. Please note that only AVRs with internal 64 MHz PLL
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oscillator can reach 16.5 MHz with the RC oscillator. This includes the very
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popular ATTiny25, ATTiny45, ATTiny85 series as well as the ATTiny26. Almost
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all AVRs can reach 12.8 MHz, although this is outside the specified range.
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See the EasyLogger example at http://www.obdev.at/vusb/easylogger.html for
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code which calibrates the RC oscillator based on the USB frame clock.
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18 MHz Clock
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This module is closer to the USB specification because it performs an on the
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fly CRC check for incoming packets. Packets with invalid checksum are
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discarded as required by the spec. If you also implement checks for data
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PID toggling on application level (see option USB_CFG_CHECK_DATA_TOGGLING
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in usbconfig.h for more info), this ensures data integrity. Due to the CRC
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tables and alignment requirements, this code is bigger than modules for other
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clock rates. To activate this module, you must define USB_CFG_CHECK_CRC to 1
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and USB_CFG_CLOCK_KHZ to 18000 in usbconfig.h.
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20 MHz Clock
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This module is for people who won't do it with less than the maximum. Since
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20 MHz is not divisible by the USB low speed bit clock of 1.5 MHz, the code
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uses similar tricks as the 16 MHz module to insert leap cycles.
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USB IDENTIFIERS
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===============
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Every USB device needs a vendor- and a product-identifier (VID and PID). VIDs
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are obtained from usb.org for a price of 1,500 USD. Once you have a VID, you
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can assign PIDs at will.
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Since an entry level cost of 1,500 USD is too high for most small companies
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and hobbyists, we provide some VID/PID pairs for free. See the file
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USB-IDs-for-free.txt for details.
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Objective Development also has some license offerings which include product
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IDs. See http://www.obdev.at/vusb/ for details.
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DEVELOPMENT SYSTEM
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==================
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This driver has been developed and optimized for the GNU compiler version 3
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and 4. We recommend that you use the GNU compiler suite because it is freely
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available. V-USB has also been ported to the IAR compiler and assembler. It
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has been tested with IAR 4.10B/W32 and 4.12A/W32 on an ATmega8 with the
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"small" and "tiny" memory model. Not every release is tested with IAR CC and
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the driver may therefore fail to compile with IAR. Please note that gcc is
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more efficient for usbdrv.c because this module has been deliberately
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optimized for gcc.
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Gcc version 3 produces smaller code than version 4 due to new optimizing
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capabilities which don't always improve things on 8 bit CPUs. The code size
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generated by gcc 4 can be reduced with the compiler options
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-fno-move-loop-invariants, -fno-tree-scev-cprop and
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-fno-inline-small-functions in addition to -Os. On devices with more than
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8k of flash memory, we also recommend the linker option --relax (written as
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-Wl,--relax for gcc) to convert absolute calls into relative where possible.
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For more information about optimizing options see:
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http://www.tty1.net/blog/2008-04-29-avr-gcc-optimisations_en.html
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These optimizations are good for gcc 4.x. Version 3.x of gcc does not support
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most of these options and produces good code anyway.
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USING V-USB FOR FREE
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====================
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The AVR firmware driver is published under the GNU General Public License
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Version 2 (GPL2) and the GNU General Public License Version 3 (GPL3). It is
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your choice whether you apply the terms of version 2 or version 3.
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If you decide for the free GPL2 or GPL3, we STRONGLY ENCOURAGE you to do the
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following things IN ADDITION to the obligations from the GPL:
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(1) Publish your entire project on a web site and drop us a note with the URL.
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Use the form at http://www.obdev.at/vusb/feedback.html for your submission.
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If you don't have a web site, you can publish the project in obdev's
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documentation wiki at
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http://www.obdev.at/goto.php?t=vusb-wiki&p=hosted-projects.
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(2) Adhere to minimum publication standards. Please include AT LEAST:
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- a circuit diagram in PDF, PNG or GIF format
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- full source code for the host software
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- a readme.txt file in ASCII format which describes the purpose of the
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project and what can be found in which directories and which files
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- a reference to http://www.obdev.at/vusb/
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(3) If you improve the driver firmware itself, please give us a free license
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to your modifications for our commercial license offerings.
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COMMERCIAL LICENSES FOR V-USB
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=============================
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If you don't want to publish your source code under the terms of the GPL,
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you can simply pay money for V-USB. As an additional benefit you get
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USB PIDs for free, reserved exclusively to you. See the file
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"CommercialLicense.txt" for details.
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