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1 This is the Readme file to Objective Development's firmware-only USB driver
2 for Atmel AVR microcontrollers. For more information please visit
3 http://www.obdev.at/vusb/
4
5 This directory contains the USB firmware only. Copy it as-is to your own
6 project and add all .c and .S files to your project (these files are marked
7 with an asterisk in the list below). Then copy usbconfig-prototype.h as
8 usbconfig.h to your project and edit it according to your configuration.
9
10
11 TECHNICAL DOCUMENTATION
12 =======================
13 The technical documentation (API) for the firmware driver is contained in the
14 file "usbdrv.h". Please read all of it carefully! Configuration options are
15 documented in "usbconfig-prototype.h".
16
17 The driver consists of the following files:
18 Readme.txt ............. The file you are currently reading.
19 Changelog.txt .......... Release notes for all versions of the driver.
20 usbdrv.h ............... Driver interface definitions and technical docs.
21 * usbdrv.c ............... High level language part of the driver. Link this
22 module to your code!
23 * usbdrvasm.S ............ Assembler part of the driver. This module is mostly
24 a stub and includes one of the usbdrvasm*.S files
25 depending on processor clock. Link this module to
26 your code!
27 usbdrvasm*.inc ......... Assembler routines for particular clock frequencies.
28 Included by usbdrvasm.S, don't link it directly!
29 asmcommon.inc .......... Common assembler routines. Included by
30 usbdrvasm*.inc, don't link it directly!
31 usbconfig-prototype.h .. Prototype for your own usbdrv.h file.
32 * oddebug.c .............. Debug functions. Only used when DEBUG_LEVEL is
33 defined to a value greater than 0. Link this module
34 to your code!
35 oddebug.h .............. Interface definitions of the debug module.
36 usbportability.h ....... Header with compiler-dependent stuff.
37 usbdrvasm.asm .......... Compatibility stub for IAR-C-compiler. Use this
38 module instead of usbdrvasm.S when you assembler
39 with IAR's tools.
40 License.txt ............ Open Source license for this driver.
41 CommercialLicense.txt .. Optional commercial license for this driver.
42 USB-ID-FAQ.txt ......... General infos about USB Product- and Vendor-IDs.
43 USB-IDs-for-free.txt ... List and terms of use for free shared PIDs.
44
45 (*) ... These files should be linked to your project.
46
47
48 CPU CORE CLOCK FREQUENCY
49 ========================
50 We supply assembler modules for clock frequencies of 12 MHz, 12.8 MHz, 15 MHz,
51 16 MHz, 16.5 MHz 18 MHz and 20 MHz. Other clock rates are not supported. The
52 actual clock rate must be configured in usbconfig.h.
53
54 12 MHz Clock
55 This is the traditional clock rate of V-USB because it's the lowest clock
56 rate where the timing constraints of the USB spec can be met.
57
58 15 MHz Clock
59 Similar to 12 MHz, but some NOPs inserted. On the other hand, the higher clock
60 rate allows for some loops which make the resulting code size somewhat smaller
61 than the 12 MHz version.
62
63 16 MHz Clock
64 This clock rate has been added for users of the Arduino board and other
65 ready-made boards which come with a fixed 16 MHz crystal. It's also an option
66 if you need the slightly higher clock rate for performance reasons. Since
67 16 MHz is not divisible by the USB low speed bit clock of 1.5 MHz, the code
68 is somewhat tricky and has to insert a leap cycle every third byte.
69
70 12.8 MHz and 16.5 MHz Clock
71 The assembler modules for these clock rates differ from the other modules
72 because they have been built for an RC oscillator with only 1% precision. The
73 receiver code inserts leap cycles to compensate for clock deviations. 1% is
74 also the precision which can be achieved by calibrating the internal RC
75 oscillator of the AVR. Please note that only AVRs with internal 64 MHz PLL
76 oscillator can reach 16.5 MHz with the RC oscillator. This includes the very
77 popular ATTiny25, ATTiny45, ATTiny85 series as well as the ATTiny26. Almost
78 all AVRs can reach 12.8 MHz, although this is outside the specified range.
79
80 See the EasyLogger example at http://www.obdev.at/vusb/easylogger.html for
81 code which calibrates the RC oscillator based on the USB frame clock.
82
83 18 MHz Clock
84 This module is closer to the USB specification because it performs an on the
85 fly CRC check for incoming packets. Packets with invalid checksum are
86 discarded as required by the spec. If you also implement checks for data
87 PID toggling on application level (see option USB_CFG_CHECK_DATA_TOGGLING
88 in usbconfig.h for more info), this ensures data integrity. Due to the CRC
89 tables and alignment requirements, this code is bigger than modules for other
90 clock rates. To activate this module, you must define USB_CFG_CHECK_CRC to 1
91 and USB_CFG_CLOCK_KHZ to 18000 in usbconfig.h.
92
93 20 MHz Clock
94 This module is for people who won't do it with less than the maximum. Since
95 20 MHz is not divisible by the USB low speed bit clock of 1.5 MHz, the code
96 uses similar tricks as the 16 MHz module to insert leap cycles.
97
98
99 USB IDENTIFIERS
100 ===============
101 Every USB device needs a vendor- and a product-identifier (VID and PID). VIDs
102 are obtained from usb.org for a price of 1,500 USD. Once you have a VID, you
103 can assign PIDs at will.
104
105 Since an entry level cost of 1,500 USD is too high for most small companies
106 and hobbyists, we provide some VID/PID pairs for free. See the file
107 USB-IDs-for-free.txt for details.
108
109 Objective Development also has some license offerings which include product
110 IDs. See http://www.obdev.at/vusb/ for details.
111
112
113 DEVELOPMENT SYSTEM
114 ==================
115 This driver has been developed and optimized for the GNU compiler version 3
116 and 4. We recommend that you use the GNU compiler suite because it is freely
117 available. V-USB has also been ported to the IAR compiler and assembler. It
118 has been tested with IAR 4.10B/W32 and 4.12A/W32 on an ATmega8 with the
119 "small" and "tiny" memory model. Not every release is tested with IAR CC and
120 the driver may therefore fail to compile with IAR. Please note that gcc is
121 more efficient for usbdrv.c because this module has been deliberately
122 optimized for gcc.
123
124 Gcc version 3 produces smaller code than version 4 due to new optimizing
125 capabilities which don't always improve things on 8 bit CPUs. The code size
126 generated by gcc 4 can be reduced with the compiler options
127 -fno-move-loop-invariants, -fno-tree-scev-cprop and
128 -fno-inline-small-functions in addition to -Os. On devices with more than
129 8k of flash memory, we also recommend the linker option --relax (written as
130 -Wl,--relax for gcc) to convert absolute calls into relative where possible.
131
132 For more information about optimizing options see:
133
134 http://www.tty1.net/blog/2008-04-29-avr-gcc-optimisations_en.html
135
136 These optimizations are good for gcc 4.x. Version 3.x of gcc does not support
137 most of these options and produces good code anyway.
138
139
140 USING V-USB FOR FREE
141 ====================
142 The AVR firmware driver is published under the GNU General Public License
143 Version 2 (GPL2) and the GNU General Public License Version 3 (GPL3). It is
144 your choice whether you apply the terms of version 2 or version 3.
145
146 If you decide for the free GPL2 or GPL3, we STRONGLY ENCOURAGE you to do the
147 following things IN ADDITION to the obligations from the GPL:
148
149 (1) Publish your entire project on a web site and drop us a note with the URL.
150 Use the form at http://www.obdev.at/vusb/feedback.html for your submission.
151 If you don't have a web site, you can publish the project in obdev's
152 documentation wiki at
153 http://www.obdev.at/goto.php?t=vusb-wiki&p=hosted-projects.
154
155 (2) Adhere to minimum publication standards. Please include AT LEAST:
156 - a circuit diagram in PDF, PNG or GIF format
157 - full source code for the host software
158 - a Readme.txt file in ASCII format which describes the purpose of the
159 project and what can be found in which directories and which files
160 - a reference to http://www.obdev.at/vusb/
161
162 (3) If you improve the driver firmware itself, please give us a free license
163 to your modifications for our commercial license offerings.
164
165
166 COMMERCIAL LICENSES FOR V-USB
167 =============================
168 If you don't want to publish your source code under the terms of the GPL,
169 you can simply pay money for V-USB. As an additional benefit you get
170 USB PIDs for free, reserved exclusively to you. See the file
171 "CommercialLicense.txt" for details.
172
Imprint / Impressum