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MicroPython port to Zephyr RTOS

This is an initial port of MicroPython to Zephyr RTOS (http://zephyrproject.org).

The port integrates well with Zephyr build system, using the latest features which will be available in 1.6.0, and thus requires Zephyr master to build against. All boards supported by Zephyr (with standard level of feature support, like UART console) should work with MicroPython (but not all were tested).

Features supported at this time:

REPL (interactive prompt) over Zephyr UART console.
utime module for time measurements and delays.
machine.Pin class for GPIO control.
"Frozen modules" support to allow to bundle Python modules together with firmware. Including complete applications, including with run-on-boot capability.

Over time, bindings for various Zephyr subsystems may be added.

Building

Follow to Zephyr web site for Getting Started instruction of installing Zephyr SDK, getting Zephyr source code, and setting up development environment. (Direct link: https://www.zephyrproject.org/doc/getting_started/getting_started.html). You may want to build Zephyr's own sample applications to make sure your setup is correct.

To build MicroPython port, in the port subdirectory (zephyr/), run:

make BOARD=<board>

If you don't specify BOARD, the default is qemu_x86 (x86 target running in QEMU emulator). Consult Zephyr documentation above for the list of supported boards.

Running

To run the resulting firmware in QEMU (for BOARDs like qemu_x86, qemu_cortex_m3):

make qemu

For deploying/flashing a firmware on a real board, follow Zephyr documentation for a given board.

Quick example

To blink an LED:

import time
from machine import Pin

LED = Pin(("GPIO_1", 21), Pin.OUT)
while True:
    LED.value(1)
    time.sleep(0.5)
    LED.value(0)
    time.sleep(0.5)

The above code uses an LED location for a FRDM-K64F board (port B, pin 21; following Zephyr conventions port are identified by "GPIO_x", where x starts from 0). You will need to adjust it for another board (using board's reference materials). To execute the above sample, copy it to clipboard, in MicroPython REPL enter "paste mode" using Ctrl+E, paste clipboard, press Ctrl+D to finish paste mode and start execution.

Minimal build

MicroPython is committed to maintain minimal binary size for Zephyr port below 128KB, as long as Zephyr project is committed to maintain stable minimal size of their kernel (which they appear to be). Note that at such size, there is no support for any Zephyr features beyond REPL over UART, and only very minimal set of builtin Python modules. Thus, this build is more suitable for code size control and quick demonstrations even on smaller systems. It's also suitable for careful enabling of features one by one to achieve needed functionality and code size. This is in contrast to the "default" build, which may get more and more features enabled by default over time.

To make a minimal build:

make BOARD=<board> minimal

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