micropython-samples

A place for assorted code ideas for MicroPython. Most are targeted at the Pyboard variants.

0. Index

1. Installation guides
   1.1 Installing MicroPython libraries
   1.2 Fastbuild Build scripts and udev rules
   1.3 Installing PicoWeb For users of official firmware
   1.4 Buildcheck Check firmware build date
2. Hardware information and drivers
   2.1 ESP32 Pinout and notes on the reference board
   2.2 SSD1306 Write large fonts to the SSD1306
   2.3 Pyboard D Assorted scraps of information
   2.4 DS3231 precision RTC Use cheap hardware to calibrate Pyboard RTC
3. Essays General thoughts
   3.1 Resilient A guide to writing resilient WiFi code
   3.2 Serialisation Review of MicroPython's four serialisation libraries
   3.3 Measurement of relative timing and phase of fast analog signals For Pyboard.
4. Code samples Samples prefixed Pyboard are Pyboard specific
   4.1 Pyboard Mutex Share data between threads and ISR's.
   4.2 Pyboard watchdog Access a Pyboard hardware WDT
   4.3 Software Watchdog Cross-platform soft WDT
   4.4 Reverse Reversal algorithms for bytearrays
   4.5 Timed function Time execution with a decorator
   4.6 ESP8266 MQTT benchmark Test performance of MQTT with official library
   4.7 Rotary incremental encoder Fast, simple, proven algorithm
   4.8 A pseudo random number generator
   4.9 Verifying incrementing sequences Test communications drivers
   4.10 Bitmaps Non-allocating ways to access bitmaps
   4.11 Functors and singletons Useful decorators
   4.12 A Pyboard power meter One of my own projects

1. Installation guides

1.1 Installing MicroPython libraries

This is more involved since the advent of the pycopy fork of MicroPython. This doc describes the issues and provides a utility to simplify installation for users of official MicroPython firmware.

1.2 Fastbuild

Scripts for building MicroPython for various target hardware types and for updating your local source. Now detects and builds for Pyboard D. See docs

1.3 Installing PicoWeb

Paul Sokolovsk's PicoWeb requires his fork of MicroPython.

Some time ago I was asked what was involved to install it on official firmware. Changes were minor. However it should be stressed that while the version here works, it is not up to date. See the Easy installation guide.

PR's with updated versions of PicoWeb are welcome.

1.4 Buildcheck

Raise an exception if a firmware build is earlier than a given date.

2. Hardware information and drivers

2.1 ESP32

Pinout diagram for the reference board with notes and warnings about reserved pins etc. See this doc.

2.2 SSD1306

A means of rendering multiple larger fonts to the SSD1306 OLED display. The Writer class which performs this has been substantially improved and may now be found as part of this repository.

2.3 Pyboard D

Assorted information not yet in the official docs).

2.4 DS3231 precision RTC

This is a low cost precision battery backed real time clock (RTC) accurate to +-2 minutes/year. Two drivers are provided, one portable across platforms and one which is Pyboard specific.

The Pyboard-specific driver provides a facility to calibrate the Pyboard's RTC from the DS3231. Calibration to high precision may be achieved in five minutes.

The drivers are documented here.

Index

3. Essays

3.1 Resilient

A guide to writing reliable ESP8266 networking code. Probably applies to other WiFi connected MicroPython devices.

3.2 Serialisation

A discussion of the need for serialisation and of the relative characteristics of four libraries available to MicroPython. Includes a tutorial on a Protocol Buffer library.

3.3 Measurement of relative timing and phase of fast analog signals

This describes ways of using the Pyboard to perform precision measurements of analog signals of up to around 50KHz. It is documented here.

Index

4. Code samples

4.1 Pyboard mutex

A class providing mutual exclusion enabling hard interrupt handlers and the main program to access shared data in a manner which ensures data integrity.

4.2 Pyboard watchdog

Access the simpler of the Pyboard's watchdog timers.

4.3 Software watchdog

A software watchdog timer with a fixed or variable timeout. Supports temporary suspension and permanent cancellation. The latter can be useful when debugging code to prevent a machine reboot when the application fails, terminates or is interrupted with ctrl-c. See code and comments in the test script.

4.4 Reverse

Fast reverse a bytearray in Arm Thumb assembler.
Also includes cross-platform Python code to bit-reverse (fast-ish) 8, 16 and 32 bit words.

4.5 Timed function

Time a function's execution using a decorator and implement timeouts using a closure.

Index

4.6 ESP8266 MQTT benchmark

This benchmark tests the performance of MQTT by periodically publishing while subscribed to the same topic. Measures the round-trip delay. Uses the official umqtt.simple library. Adapt to suit your server address and desired QOS (quality of service, 0 and 1 are supported). After 100 messages reports maximum and minimum delays.

This connect utility connects in station mode using saved connection details where possible.

4.7 Rotary Incremental Encoder

Classes for handling incremental rotary position encoders. Note Pyboard timers can do this in hardware. These samples cater for cases where that solution can't be used. The encoder_timed.py sample provides rate information by timing successive edges. In practice this is likely to need filtering to reduce jitter caused by imperfections in the encoder geometry.

There are other algorithms but this is the simplest and fastest I've encountered.

These were written for encoders producing TTL outputs. For switches, adapt the pull definition to provide a pull up or pull down as required.

The encoder_portable.py version should work on all MicroPython platforms. Tested on ESP8266. Note that interrupt latency on the ESP8266 limits performance. ESP32 has similar limitations.

4.8 A pseudo random number generator

On the Pyboard V1.1, true random numbers may be generated rapidly with pyb.rng() which uses a hardware random number generator on the microcontroller.

There are two use cases for the pseudo random number generator. Firstly on platforms lacking a hardware generator (e.g. the Pyboard Lite). And secondly where repeatable results are required, for example in testing. A pseudo random number generator is seeded with an arbitrary initial value. On each call to the function it will return a random number, but (given the same seed) the sequence of numbers following initialisation will always be the same.

See random.py for usage and timing documentation.

4.9 Verifying incrementing sequences

When testing communications applications it is often necessary to check for missing, duplicated, or out-of-order messages. To do this, the transmitter test script ensures that messages include an incrementing message number. The receiver script verifies the sequence. The CheckMid class does this, also detecting transmitter reboots

Index

4.10 Bitmaps

A bitmap stored in a pre-allocated, fixed size bytearray may be viewed in two ways:

1. As a set of positive integers whose values are constrained within limits.
2. As a fixed size one dimensional array of booleans.

These views provide a Pythonic interface while retaining the non-allocating performance advantage relative to native sets and lists.

The file bitmap.py offers classes supporting these views.

The constraint 0 <= value <= max_value applies where max_value is a constructor arg. The max_value arg defines the size of the underlying bytearray. For example if max_value is 255, the bytearray will use 32 bytes. The constraint applies to member values of a set, and to index values of a boolean array.

These classes are lightweight. For example the IntSet class does not include all the dunder (magic) methods required to match the native set class. These may readily be added as required.

4.11 Functors and singletons

Two simple class decorators for objects useful in hardware interfacing. Documented here.

Singletons denote classes for which only a single instance will ever occur. They are contentious in some circles, on the grounds that the single instance guarantee may be violated in a specification change. They can be useful in hardware contexts where a chip design is unlikely suddenly to change. Singletons denoting hardware interfaces avoid globals and the need to pass references around.

A functor is a class which is accessed via function call syntax. There is only one instance, like a singleton. Initial access calls the constructor, with subsequent accesses being via __call__. As an object it can retain state. As an example, a functor might have a continuously running task: successive calls modify the behaviour of the task.

4.12 A pyboard power meter

This uses a Pyboard to measure the power consumption of mains powered devices. Unlike simple commercial devices it performs a true vector (phasor) measurement enabling it to provide information on power factor and to work with devices which generate as well as consume power. It uses the official LCD160CR display as a touch GUI interface. It is documented here.

Index

License

Any code placed here is released under the MIT License (MIT).
The MIT License (MIT)
Copyright (c) 2016 Peter Hinch
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.