Use of MicroPython uasyncio library

This GitHub repository consists of the following parts:

• Asynchronous device drivers. A module providing drivers for devices such as switches and pushbuttons.
• Synchronisation primitives.
• A tutorial An introductory tutorial on asynchronous programming and the use of the uasyncio library is offered. This is a work in progress, not least because uasyncio is not yet complete.
• A driver for an IR remote control This is intended as an example of an asynchronous device driver. It decodes signals received from infra red remote controls using the popular NEC protocol.
• A modified uasyncio This incorporates a simple priority mechanism. With suitable application design this improves the rate at which devices can be polled and improves the accuracy of time delays.
• Communication between devices Enables MicroPython boards to communicate without using a UART. Primarily intended to enable a a Pyboard-like device to achieve bidirectional communication with an ESP8266.

Installation of uasyncio

Firstly install the latest version of micropython-uasyncio. To use queues, also install the micropython-uasyncio.queues module.

Instructions on installing library modules may be found here.

On networked hardware, upip may be run locally.

On non-networked hardware the resultant modules will need to be copied to the target. The above Unix installation will create directories under ~/.micropython/lib which may be copied to the target hardware, either to the root or to a lib subdirectory. Alternatively the device may be mounted; then use the "-p" option to upip to specify the target directory as the mounted filesystem.

Current development state

For those familiar with asyncio under CPython 3.5, uasyncio supports the following Python 3.5 features:

• async def and await syntax.
• Awaitable classes (using __iter__ rather than __await__).
• Asynchronous context managers.
• Asynchronous iterators.
• Event loop methods call_soon and call_later.
• uasyncio sleep(seconds).

It supports millisecond level timing with the following:

• Event loop method call_later_ms
• uasyncio sleep_ms(time)

It doesn't support objects of type Future and Task. Routines to run concurrently are defined as coroutines instantiated with async def and yield execution with await <awaitable>.

Asynchronous I/O and uselect

At the time of writing this was under development. Asynchronous I/O works with devices whose drivers support streaming, such as the UART. As I understand it support for select is in the pipeline. Check the current state on GitHub.

Time values

For timing asyncio uses floating point values of seconds. The uasyncio sleep method accepts floats (including sub-second values) or integers. Note that in MicroPython the use of floats implies RAM allocation which incurs a performance penalty. The design of uasyncio enables allocation-free scheduling. In applications where performance is an issue, integers should be used and the millisecond level functions (with integer arguments) employed where necessary.

The loop.time method returns an integer number of milliseconds whereas CPython returns a floating point number of seconds. call_at follows the same convention.