Over The Air

Pycom modules come with the ability to update the devices firmware, while it is still running, we call this an “over the air” (OTA) update. The pycom library provides several functions to achieve this. This example will demonstrate how you could potentially use this functionality to update deployed devices. The full source code of this example can be found here.

Pybytes

Before we talk about OTA, we need to first discuss the inner workings of the bootmgr and partitioning. The (modern) Pycom devices all have 16MB flash, divided across different partitions:

Using the function pycom.bootmgr(), we can switch between the different boot partitions. This way, we can upload a new firmware to the device and then reboot, with the boot partition switched from pycom.FACTORY to pycom.OTA_0 to load the updated firmware. We can do this using the functions: pycom.ota_start() pycom.ota_write(), pycom.ota_finish() and pycom.ota_verify().

Method A

Here we will describe one possible update methodology you could use that is implemented by this example.

Imagine you a smart metering company and you wish to roll out an update for your Pycom based smart meter. These meters usually send data back via LoRa. Unfortunately LoRa downlink messages have a very limited size and several hundred if not thousand would be required to upload a complete firmware image. To get around this you can have your devices sending their regular data via LoRa and when they receive a special command via a downlink message, the devices will connect to a WiFi network. It is unfeasible to ask customers to allow your device to connect to their home network so instead this network could be provided by a vehicle. This vehicle will travel around a certain geographic area in which the devices have been sent the special downlink message to initiate the update. The devices will look for the WiFi network being broadcast by the vehicle and connect. The devices will then connect to a server running on this WiFi network. This server (also shown in this example) will generate manifest files that instruct the device on what it should update, and where to get the update data from.

Server

This script runs a HTTP server on port 8000 that provisions over the air (OTA) update manifests in JSON format as well as serving the update content. This script should be run in a directory that contains every version of the end devices code, in the following structure:

  - server directory
    |- this_script.py
    |- 1.0.0
    |  |- flash
    |  |   |- lib
    |  |   |  |- lib_a.py
    |  |   |- main.py
    |  |   |- boot.py
    |  |- sd
    |     |- some_asset.txt
    |     |- asset_that_will_be_removed.wav
    |- 1.0.1
    |  |- flash
    |  |   |- lib
    |  |   |  |- lib_a.py
    |  |   |  |- new_lib.py
    |  |   |- main.py
    |  |   |- boot.py
    |  |- sd
    |     |- some_asset.txt
    |- firmware_1.0.0.bin
    |- firmware_1.0.1.bin

The top level directory that contains this script can contain one of two things:

How to use

Once the directory has been setup as described above you simply need to start this script using python3. Once started this script will run a HTTP server on port 8000 (this can be changed by changing the PORT variable). This server will serve all the files in directory as expected along with one additional special file, manifest.json. This file does not exist on the file system but is instead generated when requested and contains the required changes to bring the end device from its current version to the latest available version. You can see an example of this by pointing your web browser at:

The current_ver field at the end of the URL should be set to the current firmware version of the end device. The generated manifest will contain lists of which files are new, have changed or need to be deleted along with SHA1 hashes of the files. Below is an example of what such a manifest might look like:

{
   "delete": [
      "flash/old_file.py",
      "flash/other_old_file.py"
   ],
   "firmware": {
       "URL": "http://192.168.1.144:8000/firmware_1.0.1b.bin",
       "hash": "ccc6914a457eb4af8855ec02f6909316526bdd08"
   },
   "new": [
       {
           "URL": "http://192.168.1.144:8000/1.0.1b/flash/lib/new_lib.py",
           "dst_path": "flash/lib/new_lib.py",
           "hash": "1095df8213aac2983efd68dba9420c8efc9c7c4a"
       }
   ],
   "update": [
       {
           "URL": "http://192.168.1.144:8000/1.0.1b/flash/changed_file.py",
           "dst_path": "flash/changed_file.py",
           "hash": "1095df8213aac2983efd68dba9420c8efc9c7c4a"
       }
   ],
   "version": "1.0.1b"
}

In order for the URL’s to be properly formatted you are required to send a “host” header along with your HTTP get request e.g:

GET /manifest.json?current_ver=1.0.0 HTTP/1.0\r\nHost: 192.168.1.144:8000\r\n\r\n

Client Library

A MicroPyton library for interfacing with the server described above is available here.

This library is split into two layers. The top level OTA class implements all the high level functionality such as parsing the JSON file, making back copies of files being updated incase the update fails, etc. The layer of the library is agnostic to your chosen transport method. Below this is the WiFiOTA class. This class implements the actual transport mechanism of how the device fetches the files and update manifest (via WiFi as the class name suggests). The reason for this split is so that the high level functionality can be reused regardless of what transport mechanism you end up using. This could be implemented on top of Bluetooth for example, or the sever changed from HTTP to FTP.

Example

Below is am example implementing the methodology previously explained in this tutorial to initiate an OTA update.


from network import LoRa, WLAN
import socket
import time
from OTA import WiFiOTA
from time import sleep
import pycom
import ubinascii

from config import WIFI_SSID, WIFI_PW, SERVER_IP

# Turn on GREEN LED
pycom.heartbeat(False)
pycom.rgbled(0xff00)

# Setup OTA
ota = WiFiOTA(WIFI_SSID,
              WIFI_PW,
              SERVER_IP,  # Update server address
              8000)  # Update server port

# Turn off WiFi to save power
w = WLAN()
w.deinit()

# Initialise LoRa in LORAWAN mode.
lora = LoRa(mode=LoRa.LORAWAN, region=LoRa.EU868)

app_eui = ubinascii.unhexlify('70B3D57ED0008CD6')
app_key = ubinascii.unhexlify('B57F36D88691CEC5EE8659320169A61C')

# join a network using OTAA (Over the Air Activation)
lora.join(activation=LoRa.OTAA, auth=(app_eui, app_key), timeout=0)

# wait until the module has joined the network
while not lora.has_joined():
    time.sleep(2.5)
    print('Not yet joined...')

# create a LoRa socket
s = socket.socket(socket.AF_LORA, socket.SOCK_RAW)

# set the LoRaWAN data rate
s.setsockopt(socket.SOL_LORA, socket.SO_DR, 5)

# make the socket blocking
# (waits for the data to be sent and for the 2 receive windows to expire)
s.setblocking(True)

while True:
    # send some data
    s.send(bytes([0x04, 0x05, 0x06]))

    # make the socket non-blocking
    # (because if there's no data received it will block forever...)
    s.setblocking(False)

    # get any data received (if any...)
    data = s.recv(64)

    # Some sort of OTA trigger
    if data == bytes([0x01, 0x02, 0x03]):
        print("Performing OTA")
        # Perform OTA
        ota.connect()
        ota.update()

    sleep(5)

Method B

OTA software updates can be performed through the FTP server. Download the appropriate .tar.gz file for the Firmware you want to upgrade/downgrade to from here. extract the application bin file eg. (wipy.bin) for WiPy, rename that file to appimg.bin Upload the appimg.bin file to: /flash/sys/appimg.bin via your FTP client. once the file is succesfully transfered through the FTP server, the Firmware upgrade is complete and the appimg.bin file will be automatically deleted.

To boot up from the new Firmware just reset the device via Reset button or via reset Command:

OTA update from version 1.18 to 1.20

Between version 1.18.2 and 1.20 the partition table is changed, the OTA_0 partition, among several others, is relocated because the size of the firmware has been increased due to the extended functionality of the 1.20 version. Due to this reason when updating from version 1.18.2 to 1.20 via OTA, an update to an intermediate version, numbered as 1.18.3, must be performed. The intermediate version makes sure that when OTA update to 1.20 is requested, the partition table contains correct entries and the new image will be flashed to the proper location.

The intermediate version, 1.18.3, contains the following EXTRA steps when OTA update is requested:

When the device is being updated to the 1.18.3 intermediate version it may be flashed onto “OTA_0” partition depending on the where current active image is loaded from. In this case on next boot it automatically copies itself from “OTA_0” to “Factory” partition as a preparation for being able to receive the 1.20 image in the future. Without this step when the 1.20 image is being flashed on the “Factory” partition due to its increased size it would overwrite the first segments of the curently running firmware (which is the 1.18.3 and located on “OTA_0” partition).

Therefore the correct update chain from 1.18 to 1.20 via OTA looks like: 1.18.2 -> 1.18.3 -> 1.20

Downgarding from 1.20 back to 1.18 is possible, however the target version must be 1.18.3. The 1.18.3 image able to detect whether a downgrade happened and in this case it will not perform the steps explained above, it behaves as the 1.18.2r7 image just with updated partition table and bootloader. Updating back again to 1.20 is possible and allowed.