README
======

This is the README file for the port of NuttX to the Arduino Mega 2560 Rev3.

https://www.arduino.cc/en/Main/ArduinoBoardMega2560

The board is based on ATMega2560 chip from Atmel

http://www.atmel.com/devices/atmega2560.aspx

Contents
========

o Toolchain
o Serial Console
o Configurations

Toolchain
=========

Right now only Atmel's AVR8 Toolchain is supported. You can get it from

http://www.atmel.com/tools/atmelavrtoolchainforwindows.aspx

It is basically WinAVR compatible so sub-projects may define WinAVR as a
tool-chain but specify path to the Atmel AVR8 in path. See
arduino-mega2560/hello for example.

Serial Console
==============

The serial console is available on USART0. You will need to connect an
RS-232 shield or an external RS-232 driver as follows:

TXD: TX0->1
RXD: RX0->0
GND: Power GND
+5V: Power +5V

You will then need to use a terminal program configured at 38400 8N1.

Configurations
==============

Common Configuration Notes
--------------------------
1. Each Arduino MEGA2560 configuration is maintained in a sub-directory
and can be selected as follow:

tools/configure.sh arduino-mega2560/

Where is one of the configuration sub-directories described in
the following paragraph.

2. These configurations use the mconf-based configuration tool. To
change a configurations using that tool, you should:

a. Build and install the kconfig-mconf tool. See nuttx/README.txt
see additional README.txt files in the NuttX tools repository.

b. Execute 'make menuconfig' in nuttx/ in order to start the
reconfiguration process.

3. By default, all configurations assume the Atmel Studio AVR8 toolchain
under Cygwin with Windows. This is easily reconfigured:

CONFIG_HOST_WINDOWS=y
CONFIG_WINDOWS_CYGWIN=y
CONFIG_AVR_BUILDROOT_TOOLCHAIN=y

Configuration Sub-Directories
-----------------------------
hello:
The simple apps/examples/hello "Hello, World!" example.

nsh:
This is a reduce NuttShell (NSH) configuration using apps/example/nsh.
The serial console is provided on USART0 and can be accessed via
an external RS-232 driver as described above under "Serial Console".

NOTES:

1. As of 2015-01-16, the default static memory usage is:

$ size nuttx.elf
text data bss dec hex filename
34348 2117 944 37409 9221 nuttx.elf

And dynamic, heap usage:

nsh> free
total used free largest
Mem: 4736 1768 2968 2968

There is plenty of FLASH space but not a lot of free SRAM. This
SRAM usage is due primarily to constant strings defined by NSH.

NOTE: I investigated the possibility of adding IPTR/IOBJ
qualifiers in the NSH library and moving the strings to FLASH.
This is still a possibility but would requires some extensive
changes to NSH.