47 lines
2.1 KiB
ReStructuredText
47 lines
2.1 KiB
ReStructuredText
===========
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AVR AT90USB
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===========
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AVR AT90USB64x and AT90USB6128x
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-------------------------------
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**Micropendous 3 AT90USB64x** and **AT90USB6128x**. This port of NuttX
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to the Opendous Micropendous 3 board. The Micropendous3 is may be
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populated with an AT90USB646, 647, 1286, or 1287. I have only the
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AT90USB647 version for testing. This version have very limited memory
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resources: 64K of FLASH and 4K of SRAM.
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**PJRC Teensy++ 2.0 AT90USB1286**. This is a port of NuttX to the PJRC
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Teensy++ 2.0 board. This board was developed by
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`PJRC <http://pjrc.com/teensy/>`__. The Teensy++ 2.0 is based on an
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Microchip AT90USB1286 MCU.
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**AVR-Specific Issues**. The basic AVR port is solid. The biggest issue
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for using AVR is its tiny SRAM memory and its Harvard architecture.
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Because of the Harvard architecture, constant data that resides to flash
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is inaccessible using "normal" memory reads and writes (only SRAM data
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can be accessed "normally"). Special AVR instructions are available for
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accessing data in FLASH, but these have not been integrated into the
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normal, general purpose OS.
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Most NuttX test applications are console-oriented with lots of strings
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used for ``printf()`` and debug output. These strings are all stored in
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SRAM now due to these data accessing issues and even the smallest
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console-oriented applications can quickly fill a 4-8K memory. So, in
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order for the AVR port to be useful, one of two things would need to be
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done:
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#. Don't use console applications that required lots of strings. The
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basic AVR port is solid and your typical deeply embedded application
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should work fine. Or,
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#. Create a special version of printf that knows how to access strings
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that reside in FLASH (or EEPROM).
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**Development Environments:** 1) Linux with native Linux GNU toolchain,
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2) Cygwin/MSYS with Cygwin GNU toolchain, 3) Cygwin/MSYS with Windows
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native toolchain, or 4) Native Windows. All testing, however, has been
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performed using the NuttX DIY toolchain for Linux or Cygwin is provided
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by the NuttX
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`buildroot <https://bitbucket.org/nuttx/buildroot/downloads/>`__
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package. As a result, that toolchain is recommended.
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