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The MicroPython project

The LoPy

This is the MicroPython project, which aims to put an implementation of Python 3.x on microcontrollers and small embedded systems. You can find the official website at micropython.org.

WARNING: this project is in beta stage and is subject to changes of the code-base, including project-wide name changes and API changes.

MicroPython implements the entire Python 3.4 syntax (including exceptions, "with", "yield from", etc., and additionally "async" keyword from Python 3.5). The following core datatypes are provided: str (including basic Unicode support), bytes, bytearray, tuple, list, dict, set, frozenset, array.array, collections.namedtuple, classes and instances. Builtin modules include sys, time, and struct, etc. Select ports have support for _thread module (multithreading). Note that only subset of Python 3.4 functionality implemented for the data types and modules.

See the repository www.github.com/micropython/pyboard for the MicroPython board (PyBoard), the officially supported reference electronic circuit board.

The following components are actively maintained by Pycom:

  • py/ -- the core Python implementation, including compiler, runtime, and core library.
  • exp32/ -- a version of MicroPython that runs on the ESP32 based boards from Pycom.
  • tests/ -- test framework and test scripts.

Additional components:

  • stmhal/ -- a version of MicroPython that runs on the PyBoard and similar STM32 boards (using ST's Cube HAL drivers).
  • minimal/ -- a minimal MicroPython port. Start with this if you want to port MicroPython to another microcontroller.
  • bare-arm/ -- a bare minimum version of MicroPython for ARM MCUs. Used mostly to control code size.
  • teensy/ -- a version of MicroPython that runs on the Teensy 3.1 (preliminary but functional).
  • pic16bit/ -- a version of MicroPython for 16-bit PIC microcontrollers.
  • cc3200/ -- a version of MicroPython that runs on the CC3200 from TI.
  • esp8266/ -- an experimental port for ESP8266 WiFi modules.
  • tools/ -- various tools, including the pyboard.py module.
  • examples/ -- a few example Python scripts.
  • docs/ -- user documentation in Sphinx reStructuredText format.

The subdirectories above may include READMEs with additional info.

"make" is used to build the components, or "gmake" on BSD-based systems. You will also need bash and Python (at least 2.7 or 3.3).

The ESP32 version

The "esp32" port requires an xtensa gcc compiler, which can be downloaded from the Espressif website:

To use it, you will need to update your PATH environment variable in ~/.bash_profile file. To make xtensa-esp32-elf available for all terminal sessions, add the following line to your ~/.bash_profile file::

export PATH=$PATH:$HOME/esp/xtensa-esp32-elf/bin

Alternatively, you may create an alias for the above command. This way you can get the toolchain only when you need it. To do this, add different line to your ~/.bash_profile file::

alias get_esp32="export PATH=$PATH:$HOME/esp/xtensa-esp32-elf/bin"

Then when you need the toolchain you can type get_esp32 on the command line and the toolchain will be added to your PATH.

You also need the ESP IDF along side this repository in order to build the ESP32 port. To get it:

$ git clone https://github.com/pycom/pycom-esp-idf.git

After cloning, make sure to checkout all the submodules:

$ cd pycom-esp-idf
$ git submodule update --init

Finally, before building, export the IDF_PATH variable

$ export IDF_PATH=~/pycom-esp-idf

This repository contains submodules! Clone using the --recursive option:

$ git clone --recursive https://github.com/pycom/pycom-micropython-sigfox.git

Alternatively checkout the modules manually:

$ cd pycom-micropython-sigfox
$ git submodule update --init
If you updated the repository from a previous revision and/or if switching between branches,<br>
make sure to also update the submodules with the command above.

Prior to building the main firmware, you need to build mpy-cross

$ cd mpy-cross && make clean && make && cd ..

By default the firmware is built for the WIPY2:

$ cd esp32
$ make clean
$ make TARGET=boot
$ make TARGET=app
$ make flash

You can change the board type by using the BOARD variable:

$ cd esp32
$ make BOARD=GPY clean
$ make BOARD=GPY TARGET=boot
$ make BOARD=GPY TARGET=app
$ make BOARD=GPY flash

We currently support the following BOARD types:

WIPY LOPY SIPY GPY FIPY LOPY4

For LoRa, you may need to specify the LORA_BAND as explained below.

To specify a serial port other than /dev/ttyUSB0, use ESPPORT variable:

$ # On MacOS
$ make ESPPORT=/dev/tty.usbserial-DQ008HQY flash
$ # On Windows
$ make ESPPORT=COM3 flash
$ # On linux
$ # make ESPPORT=/dev/ttyUSB1 flash

To flash at full speed, use ESPSPEED variable:

$ make ESPSPEED=921600 flash

To build and flash a LoPy:

$ cd esp32
$ make BOARD=LOPY clean
$ make BOARD=LOPY TARGET=boot
$ make BOARD=LOPY TARGET=app
$ make BOARD=LOPY flash

The above also applies to the FiPy and LoPy4

Make sure that your board is placed into programming mode, otherwise flashing will fail.
PyTrack and PySense boards will automatically switch into programming mode
(currently supported on MacOS and Linux only!)

Expansion Board 2.0 users, please connect P2 to GND and then reset the board.

Steps for using Secure Boot and Flash Encryption

Summary

  1. Obtain keys (for Secure Boot and Flash Encryption)
  2. Flash keys and parameters in efuses
  3. Compile bootloader and application with make SECURE=on
  4. Flash: bootloader-digest at address 0x0 and encrypted; all the others (partitions and application) encrypted, too.

Prerequisites

$ export IDF_PATH=<pycom-esp-idf_PATH>
$ cd esp32

Hold valid keys for Flash Encryption and Secure Boot; they can be generated randomly with the following commands:

python $IDF_PATH/components/esptool_py/esptool/espsecure.py generate_flash_encryption_key flash_encryption_key.bin
python $IDF_PATH/components/esptool_py/esptool/espsecure.py generate_signing_key secure_boot_signing_key.pem

The Secure Boot key secure_boot_signing_key.pem has to be transformed into secure-bootloader-key.bin, to be burnt into efuses. This can be done in 2 ways:

python $IDF_PATH/components/esptool_py/esptool/espsecure.py extract_public_key --keyfile secure_boot_signing_key.pem signature_verification_key.bin

# or, as an artifact of the make build process, on the same directory level as Makefile
make BOARD=GPY SECURE=on TARGET=boot

Flash keys (flash_encryption_key.bin and secure-bootloader-key.bin) into the efuses (write and read protected):

Note: Irreversible operations

# Burning Encryption Key
python $IDF_PATH/components/esptool_py/esptool/espefuse.py --port /dev/ttyUSB0 burn_key flash_encryption flash_encryption_key.bin
# Burning Secure Boot Key
python $IDF_PATH/components/esptool_py/esptool/espefuse.py --port /dev/ttyUSB0 burn_key secure_boot secure-bootloader-key.bin
# Enabling Flash Encryption mechanism
python $IDF_PATH/components/esptool_py/esptool/espefuse.py --port /dev/ttyUSB0 burn_efuse FLASH_CRYPT_CNT
# Configuring Flash Encryption to use all address bits togheter with Encryption key (max value 0x0F)
python $IDF_PATH/components/esptool_py/esptool/espefuse.py --port /dev/ttyUSB0 burn_efuse FLASH_CRYPT_CONFIG 0x0F
# Enabling Secure Boot mechanism
python $IDF_PATH/components/esptool_py/esptool/espefuse.py --port /dev/ttyUSB0 burn_efuse ABS_DONE_0

If the keys are not written in efuse, before flashing the bootloader, then random keys will be generated by the ESP32, they can never be read nor re-written, so bootloader can never be updated. Even more, the application can be re-flashed (by USB) just 3 more times.

Makefile options:

make BOARD=GPY SECURE=on SECURE_KEY=secure_boot_signing_key.pem ENCRYPT_KEY=flash_encryption_key.bin TARGET=[boot|app]
  • SECURE=on is the main flag; it's not optional
  • if SECURE=on by default:
    • encryption is enabled
    • secure_boot_signing_key.pem is the secure boot key, located relatively to Makefile
    • flash_encryption_key.bin is the flash encryption key, located relatively to Makefile

For flashing the bootloader digest and the encrypted versions of all binaries:

make BOARD=GPY SECURE=on flash

Flashing

For flashing the bootloader-reflash-digest.bin has to be written at address 0x0, instead of the bootloader.bin (at address 0x1000).

Build is done using SECURE=on option; additionally, all the binaries are pre-encrypted.

make BOARD=GPY clean
make BOARD=GPY SECURE=on TARGET=boot
make BOARD=GPY SECURE=on TARGET=app
make BOARD=GPY SECURE=on flash

Manual flash command:

python $IDF_PATH/components/esptool_py/esptool/esptool.py --chip esp32 --port /dev/ttyUSB0 --baud 921600 --before no_reset --after no_reset write_flash -z --flash_mode dio --flash_freq 80m --flash_size detect 0x0 build/GPY/release/bootloader/bootloader-reflash-digest.bin_enc 0x8000 build/GPY/release/lib/partitions.bin_enc 0x10000 build/GPY/release/gpy.bin_enc_0x10000

OTA update

The OTA should be done using the pre-encrypted application image.

Because the encryption is done based on the physical flash address, there are 2 application binaries generated:

  • gpy.bin_enc_0x10000 which has to be written at default factory address: 0x10000
  • gpy.bin_enc_0x1A0000 which has to be written at the ota_0 partition address (0x1A0000)

Hint: on micropython interface, the method pycom.ota_slot() responds with the address of the next OTA partition available (either 0x10000 or 0x1A0000).

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