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/** \mainpage AVRISP MKII Programmer Project
 *
 *  \section Sec_Compat Project Compatibility
 *
 *  The following list indicates what microcontrollers are compatible with this project.
 *
 *  \li Series 7 USB AVRs (AT90USBxxx7)
 *  \li Series 6 USB AVRs (AT90USBxxx6)
 *  \li Series 4 USB AVRs (ATMEGAxxU4)
 *  \li Series 2 USB AVRs (AT90USBxx2, ATMEGAxxU2) - <i>8KB versions with reduced features only</i>
 *
 *  \section Sec_Info USB Information
 *
 *  The following table gives a rundown of the USB utilization of this project.
 *
 * <table>
 *  <tr>
 *   <td><b>USB Mode:</b></td>
 *   <td>Device</td>
 *  </tr>
 *  <tr>
 *   <td><b>USB Class:</b></td>
 *   <td>Vendor Specific Class</td>
 *  </tr>
 *  <tr>
 *   <td><b>USB Subclass:</b></td>
 *   <td>N/A</td>
 *  </tr>
 *  <tr>
 *   <td><b>Relevant Standards:</b></td>
 *   <td>Atmel AVRISP MKII Protocol Specification</td>
 *  </tr>
 *  <tr>
 *   <td><b>Supported USB Speeds:</b></td>
 *   <td>Full Speed Mode</td>
 *  </tr>
 * </table>
 *
 *  \section Sec_Description Project Description
 *
 *  Firmware for an Atmel Studio compatible AVRISP-MKII clone programmer. This project will enable the USB
 *  AVR series of microcontrollers to act as a clone of the official Atmel AVRISP-MKII programmer, usable within
 *  Atmel Studio or with any software capable of driving a real Atmel AVRISP-MKII programmer. In its most
 *  basic form, it allows for the programming of AVR TINY, MEGA and XMEGA devices at the programmer's VCC voltage from
 *  within Atmel Studio with no special hardware other than the USB AVR and the parts needed for the USB
 *  interface. If the user desires, more advanced circuits incorporating level conversion can be made to allow for the
 *  programming of target AVRs running at a different voltage to the programmer.
 *
 *  This device spoofs Atmel's official AVRISP-MKII device PID so that it remains compatible with Atmel's AVRISP-MKII
 *  drivers. It is currently tested working under the following configurations:
 *
 *    - <b>Windows:</b> Atmel Studio 7, with alternative driver
 *    - <b>Windows:</b> AVRDUDE 6.2, with alternative driver
 *    - <b>Linux:</b> AVRDUDE 6.1
 *
 *  <b>Note that this clone requires a libUSB based driver under Windows,</b> due to an incompatible change in the official
 *  Jungo based driver. The alternative driver given here will function with both real and clone AVRISP devices in Atmel
 *  Studio 7 onwards under Windows - and as a bonus, also provides AVRDude access to the programmer.
 *
 *  As of Atmel Studio version 7.0.1417 the legacy Jungo driver has been deprecated in favor of an official libUSB based
 *  driver, making the driver packaged here superfluous. Use the driver packaged here only if you are still using an earlier
 *  Atmel Studio 7 build, otherwise the official Atmel libUSB driver should be used.
 *
 *  Note that this design currently has the following limitations:
 *    - No reversed/shorted target connector detection and notification
 *    - A separate header is required for each of the ISP, PDI and TPI programming protocols that the user wishes to use
 *
 *  On AVR models with an ADC converter, the USB AVR's AVCC pin should be tied to 5V (e.g. VBUS) and the
 *  \c VTARGET_ADC_CHANNEL token should be set to an appropriate ADC channel number in the project makefile for VTARGET
 *  detection to operate correctly. On models without an ADC converter, VTARGET will report a fixed 3.3V level at all times
 *  which should allow the programmer to remain compatible at the protocol level with all AVR devices.
 *
 *  While this application can be compiled for USB AVRs with as little as 8KB of FLASH, for full functionality 16KB or more
 *  of FLASH is required. On 8KB devices, ISP or PDI/TPI protocol programming support can be disabled to reduce program size.
 *
 *  \section Sec_Installation Installation
 *  The programmer supports multiple platforms, both Windows and Linux.
 *
 *  \subsection SSec_LinuxInstallation Linux Installation
 *  On Linux systems, the programmer should be usable out of the box with no special setup other than (on some systems)
 *  editing of the system permissions to allow the programmer to be used from a non-elevated (root) context. The programmer
 *  is compatible with the free open source AVRDude programming software project.
 *
 *  \subsection SSec_WindowsInstallation Windows Installation
 *  On Windows systems, due to an unfortunate limitation of the USB AVR devices and the Atmel Studio platform, the programmer
 *  requires an alternative libUSB based driver. Uninstall the existing Jungo driver for the device (if installed) and replace
 *  it with the driver that ships with this project, to enable access to the programmer in Atmel Studio and AVRDUDE.
 *
 *  \section Sec_ISP ISP Connections
 *  Connections to the device for SPI programming (when enabled):
 *
 *  <table>
 *   <tr>
 *    <th><b>Programmer Pin:</b></th>
 *    <th><b>Target Device Pin:</b></th>
 *    <th><b>ISP 6 Pin Layout:</b></th>
 *   </tr>
 *   <tr>
 *    <td>MISO</td>
 *    <td>PDO</td>
 *    <td>1</td>
 *   </tr>
 *   <tr>
 *    <td>ADCx <b><sup>1</sup></b></td>
 *    <td>VTARGET</td>
 *    <td>2</td>
 *   </tr>
 *   <tr>
 *    <td>SCLK</td>
 *    <td>SCLK</td>
 *    <td>3</td>
 *   </tr>
 *   <tr>
 *    <td>MOSI</td>
 *    <td>PDI</td>
 *    <td>4</td>
 *   </tr>
 *   <tr>
 *    <td>PORTx.y <b><sup>2</sup></b></td>
 *    <td>/RESET</td>
 *    <td>5</td>
 *   </tr>
 *   <tr>
 *    <td>GND</td>
 *    <td>GND</td>
 *    <td>6</td>
 *   </tr>
 *  </table>
 *
 *  In addition, the AVR's OCR1A pin will generate a 4MHz clock, to act as an external rescue device clock if the
 *  fuses have been mis-set. To use the recovery clock, connect the OCR1A pin of the USB AVR to the target AVR's
 *  XTAL1 pin, and set the ISP programming speed to 125KHz (note: other ISP speeds will not work correctly).
 *
 *  <b><sup>1</sup></b> <i>Optional, see \ref Sec_Options section - for USB AVRs with ADC modules only</i> \n
 *  <b><sup>2</sup></b> <i>See AUX line related tokens in the \ref Sec_Options section</i>
 *
 *  \section Sec_PDI PDI Connections
 *  Connections to the device for PDI programming (when enabled):
 *
 *  <table>
 *   <tr>
 *    <th><b>Programmer Pin:</b></th>
 *    <th><b>Target Device Pin:</b></th>
 *    <th><b>PDI 6 Pin Layout:</b></th>
 *   </tr>
 *   <tr>
 *    <td>Tx/Rx <b><sup>2</sup></b></td>
 *    <td>DATA</td>
 *    <td>1</td>
 *   </tr>
 *   <tr>
 *    <td>ADCx <b><sup>1</sup></b></td>
 *    <td>VTARGET</td>
 *    <td>2</td>
 *   </tr>
 *   <tr>
 *    <td>N/A</td>
 *    <td>N/A</td>
 *    <td>3</td>
 *   </tr>
 *   <tr>
 *    <td>N/A</td>
 *    <td>N/A</td>
 *    <td>4</td>
 *   </tr>
 *   <tr>
 *    <td>XCK</td>
 *    <td>CLOCK</td>
 *    <td>5</td>
 *   </tr>
 *   <tr>
 *    <td>GND</td>
 *    <td>GND</td>
 *    <td>6</td>
 *   </tr>
 *  </table>
 *
 *  <b><sup>1</sup></b> <i>Optional, see \ref Sec_Options section - for USB AVRs with ADC modules only</i> \n
 *  <b><sup>2</sup></b> <i>The AVR's Tx and Rx become the DATA line when connected together via a pair of 220 ohm resistors</i> \n
 *
 *  \section Sec_TPI TPI Connections
 *  Connections to the device for TPI programming (when enabled):
 *
 *  <table>
 *   <tr>
 *    <th><b>Programmer Pin:</b></th>
 *    <th><b>Target Device Pin:</b></th>
 *    <th><b>TPI 6 Pin Layout:</b></th>
 *   </tr>
 *   <tr>
 *    <td>Tx/Rx <b><sup>2</sup></b></td>
 *    <td>DATA</td>
 *    <td>1</td>
 *   </tr>
 *   <tr>
 *    <td>ADCx <b><sup>1</sup></b></td>
 *    <td>VTARGET</td>
 *    <td>2</td>
 *   </tr>
 *   <tr>
 *    <td>XCK <b><sup>2</sup></b></td>
 *    <td>CLOCK</td>
 *    <td>3</td>
 *   </tr>
 *   <tr>
 *    <td>N/A</td>
 *    <td>N/A</td>
 *    <td>4</td>
 *   </tr>
 *   <tr>
 *    <td>PORTx.y <b><sup>3</sup></b></td>
 *    <td>/RESET</td>
 *    <td>5</td>
 *   </tr>
 *   <tr>
 *    <td>GND</td>
 *    <td>GND</td>
 *    <td>6</td>
 *   </tr>
 *  </table>
 *
 *  <b><sup>1</sup></b> <i>Optional, see \ref Sec_Options section - for USB AVRs with ADC modules only</i> \n
 *  <b><sup>2</sup></b> <i>The AVR's Tx and Rx become the DATA line when connected together via a pair of 220 ohm resistors</i> \n
 *  <b><sup>3</sup></b> <i>See AUX line related tokens in the \ref Sec_Options section</i>
 *
 *  \section Sec_Options Project Options
 *
 *  The following defines can be found in this project, which can control the project behaviour when defined, or changed in value.
 *
 *  <table>
 *   <tr>
 *    <th><b>Define Name:</b></th>
 *    <th><b>Location:</b></th>
 *    <th><b>Description:</b></th>
 *   </tr>
 *   <tr>
 *    <td>AUX_LINE_PORT</td>
 *    <td>AppConfig.h</td>
 *    <td>PORT register for the programmer's AUX target line. The use of this line varies between the programming protocols,
 *        but is generally used for the target's /RESET line.
 *        \n \n <i>Ignored when compiled for the XPLAIN board.</i></td>
 *   </tr>
 *   <tr>
 *    <td>AUX_LINE_PIN</td>
 *    <td>AppConfig.h</td>
 *    <td>PIN register for the programmer's AUX target line. The use of this line varies between the programming protocols,
 *        but is generally used for the target's /RESET line.
 *        \n \n <i>Ignored when compiled for the XPLAIN board.</i></td>
 *   </tr>
 *   <tr>
 *    <td>AUX_LINE_DDR</td>
 *    <td>AppConfig.h</td>
 *    <td>DDR register for the programmer's AUX target line. The use of this line varies between the programming protocols,
 *        but is generally used for the target's /RESET line.
 *        \n \n <i>Ignored when compiled for the XPLAIN board.</i></td>
 *   </tr>
 *   <tr>
 *    <td>AUX_LINE_MASK</td>
 *    <td>AppConfig.h</td>
 *    <td>Mask for the programmer's AUX target line. The use of this line varies between the programming protocols,
 *        but is generally used for the target's /RESET line. <b>Must not be the AVR's /SS pin</b>.
 *        \n \n <i>Ignored when compiled for the XPLAIN board.</i></td>
 *   </tr>
 *   <tr>
 *    <td>VTARGET_ADC_CHANNEL</td>
 *    <td>AppConfig.h</td>
 *    <td>ADC channel number (on supported AVRs) to use for VTARGET level detection, if NO_VTARGET_DETECT is not defined.
 *        \n \n <i>Ignored when compiled for targets lacking an ADC.</i></td>
 *   </tr>
 *   <tr>
 *    <td>ENABLE_ISP_PROTOCOL</td>
 *    <td>AppConfig.h</td>
 *    <td>Define to enable SPI programming protocol support.
 *        \n \n <i>Ignored when compiled for the XPLAIN board.</i></td>
 *   </tr>
 *   <tr>
 *    <td>ENABLE_XPROG_PROTOCOL</td>
 *    <td>AppConfig.h</td>
 *    <td>Define to enable PDI and TPI programming protocol support.
 *        \n \n <i>Ignored when compiled for the XPLAIN board.</i></td>
 *   </tr>
 *   <tr>
 *    <td>NO_VTARGET_DETECT</td>
 *    <td>AppConfig.h</td>
 *    <td>Define to disable VTARGET sampling and reporting on AVR models with an ADC converter. This will cause the programmer
 *        to report a fixed 3.3V target voltage to the host regardless of the real target voltage.
 *        \n \n <i>Ignored when compiled for targets lacking an ADC.</i></td>
 *   </tr>
 *   <tr>
 *    <td>VTARGET_REF_VOLTS</td>
 *    <td>AppConfig.h</td>
 *    <td>Indicates the programmer AVR's AVCC reference voltage when measuring the target's supply voltage. Note that the supply
 *        voltage should never exceed the reference voltage on the programmer AVR without some form of protection to prevent damage
 *        to the ADC.
 *        \n \n <i>Ignored when compiled for targets lacking an ADC, or when NO_VTARGET_DETECT is defined.</i></td>
 *   </tr>
 *   <tr>
 *    <td>VTARGET_USE_INTERNAL_REF</td>
 *    <td>AppConfig.h</td>
 *    <td>Selects the internal 2.56V ADC reference voltage, instead of using the AVR's VREF pin. When enabled, this option will
 *        override the VTARGET_REF_VOLTS configuration option.
 *        \n \n <i>Ignored when compiled for targets lacking an ADC, or when NO_VTARGET_DETECT is defined.</i></td>
 *   </tr>
 *   <tr>
 *    <td>VTARGET_SCALE_FACTOR</td>
 *    <td>AppConfig.h</td>
 *    <td>Indicates the target's supply voltage scale factor when applied to the ADC. A simple resistive divider can be used on the
 *        ADC pin for measuring the target's supply voltage, so that voltages above the programmer AVR's AVCC reference voltage can be
 *        measured. This should be the reciprocal of the division performed - e.g. if the VTARGET voltage is halved, this should be set
 *        to 2.
 *        \n \n <i>Ignored when compiled for targets lacking an ADC, or when NO_VTARGET_DETECT is defined.</i></td>
 *   </tr>
 *   <tr>
 *    <td>XCK_RESCUE_CLOCK_ENABLE</td>
 *    <td>AppConfig.h</td>
 *    <td>Define to move the ISP rescue clock to the AVR's XCK pin instead of the OCR1A output pin. This is useful for existing programming
 *        hardware that does not expose the OCR1A pin of the AVR, but <i>may</i> cause some issues with PDI programming mode.</td>
 *   </tr>
 *   <tr>
 *    <td>INVERTED_ISP_MISO</td>
 *    <td>AppConfig.h</td>
 *    <td>Define to invert the received data on the ISP MISO line. This is sometimes needed depending on the level translation hardware used,
 *        if the translator hardware inverts the received logic level.</td>
 *   </tr>
 *   <tr>
 *    <td>FIRMWARE_VERSION_MINOR</td>
 *    <td>AppConfig.h</td>
 *    <td>Define to set the minor firmware revision nunber reported to the host on request. By default this will use a firmware version compatible
 *        with the latest Atmel IDE version, however if desired the reported minor value can be adjusted here.</td>
 *   </tr>
 *  </table>
 */