A small, real time OS for ARM Cortex-M4F microcontrollers.

Originally developed for the STM32F4DISCOVERY, but should work
just fine on any STM32F40x microcontroller.  Other STM32F4s should
be very easy to port to.

Initial support has also been added for TI LM4F120H5 microcontrollers
(TI Stellaris Launchpad).  Fewer peripherals have been developed, but
the core OS works well.

It should be possible to port to additional Cortex M4F cores simply
by using the two board/ folders as an example.  The core of what is
needed is a clock initialization function, and drivers for desired
peripherals.

Building requires arm-none-eabi-toolchain.  For hardfloat support, see
https://github.com/prattmic/arm-cortex-m4-hardfloat-toolchain or
https://launchpad.net/gcc-arm-embedded.

Specify the device you are building for using the BOARD environmental
variable.  For example, to build for the LM4F120H5, run 'BOARD=lm4f120h5 make'.
By default, make builds with BOARD=stm32f40x.

For flashing and debugging on the STM32F40x, texane's stlink is 
recommended: https://github.com/texane/stlink

With stlink in your path, "make burn" will flash your device.

For the LM4F120H5, I have used the JLink JTAG debugger, which
'make burn' will attempt to use.  The Stellaris Launchpad also has an
integrated debugger, which you should be able to use with lm4tools:
https://github.com/utzig/lm4tools

'make burn' calls flash.sh in the board folder, so modify it to
your heart's content.

By default, the shell program in usr/shell/ is built and run at
boot.  The main() function in main.c is called by the scheduler
before task switching begins and should be used to create tasks
that run at boot.

On the STM32F40x, resource 0 (stdin/out) is the USB device, which 
should appear as a USB CDC ACM (Virtual Terminal) device on the host.
Resource 1 (stderr) is the UART on PB6 (TX) and PB7 (RX).  The default 
resources can be changed in the board.c file for each board.

On the LM4F120H5, resources 0 and 1 are defaulted to UART0 on PA0 and PA1.

Michael Pratt