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