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Tock Tutorial Rust Nation UK

The purpose of this turtorial is to build a simple smarthome device.

To work, the smarthome device has the folllowing components:

  1. a smarthome kernel driver that will act as the data model
  2. a smarthome service that will pull the data from the sensors (doors, temperature) and send the it to the driver for storing
  3. a ui app that displays the doors status and the temperature

Smarthome

For this tutorial you will have to implements the driver (1) and the service (2). The UI app (3) is already implemented using the C/C++ language.

Folders

This template has the kernel and upser space applications in the same repository. The organization is the following:

  • kernel - everything related to the kernel
    • tock - the Tock kernel repository
    • smarthome - the entry point (main.rs) for the smarthome kernel
    • drivers - drivers that we want to include in the kernel
  • applications - everything that is required for applications
    • c - C applications
      • libtock-c - the C library for Tock applications
      • example_app - an example app
      • drivers - libraries for the drivers that we added to the kernel
      • ui - the UI application that displays the doors status and the temperature
    • rust - Rust applications
      • libtock-rs the Rust library for Tock applications
      • example_app - an example app
      • service - the service app that we implement
  • build - the build folder where the UF2 files are placed

Driver

Write a Tock driver that acts like a model for the smarthome. It stores:

Value Description Data Type
door_a The status of the door connected to buttton A bool
door_b The status of the door connected to buttton B bool
temperature The temperature in hundreds of centigrades i32

The driver exposes the following API:

Cmd Description Data 1 Data 2 Return
0 Driver exists N/A N/A success
101 Stores the status of the doors Door A Door B success
102 Stores the temperature temperature in hunderds of centigrades N/A success
201 Returns the status of the doors N/A N/A success_u32_u32
202 Returns the temperature N/A N/A success_u32

Write the driver

The first step in writing the driver is to define a data structure Smarthome that stores the data.

The second step is to implement the SyscallDriver trait for Smarthome.

Hint: As the SyscallDriver trait uses &self for its methods, you have to use interior mutability to store the data.

Register the driver

To use the driver, it has to be registered with the board, meaning it has to be instatiated in main.rs. Follow the staps to to this:

  1. Define the driver in the PicoExplorerBase structure.
  2. Connect the smarthome::DRIVER_NUM to the kernel by adding it in the with_driver function
  3. Instantiate the driver in the main function

Hint: use static_init! get a reference to the driver

Build the kernel

To build the kernel run make in the smarthome folder.

Flash the kernel

To flash the kernel to the board, run the make kernel. This will create a UF2 file in build/kernel.uf2. Copy this file to the Pi's USB driver.

To connect the PI's USB drive, disconnect the micri usb cable from the Pi, press and hold the BOOTSEL button and connect the micro usb cable. Release the BOOTSEL button. A USB driver should become available.

Process Console

Tock offers a simple command line to manage processes. To access it, run a serial terminal and connect to the virtual USB port using a 115200 baudrate.

To easiest way to connect to the board is to use tockloader. To install tockloader run pip3 install tockloader.

Note You might have to use sudo to install

If tockloader is not working, use:

OS Software
Windows putty.exe
Linux screen
macOS screen

Software reset

To avoid puggin in and out the USB cable, you can reset the board using the process console.

Press and hold the BOOTSEL button and run the reset command in process console. Release the BOOTSEL button.

tock$ reset

Service (Rust)

Write a rust application that implements the logic of the smart home.

Build

To build the app, run make raspberry_pi_pico in the app folder.

Driver API

The first step is to implement the driver API that talks to the smarthome driver.

Use the exists function example tom implement the setting of the doors status and the temperature.

Service

Implement the services as an infinte loop that does the following:

  1. reads the door statuses
  2. sends the statuses to the driver
  3. reads the temperature
  4. sends the it to the driver
  5. waits for a few milliseconds

Flashing the apps

The smarthome will run two apps:

  • the UI app
  • the service app

To load both of the app, the make app command does the following:

  • builds the kernel as an ELF file
  • builds the UI app as a TBF file
  • builds the service app as a TBF file
  • merges the two TBF files (UI and service, in this order)
  • writes the merged TBFs as the .apps section of the kernel ELF file
  • converts the ELF file to a UF2

Relocation

While the UI app is relocatable, meaning that it can be loaded at any address, the service app is not. It uses a fixed loading address where it loads. That address depends on the size of the UI app. To figure out the address that the Rust app has to ooad to, follow:

  • enable the debug_load_processes feature for the kernel crate
  • load the UF2 file with the apps
  • the kernel will print the required address
    • first it prints the Flash address, modify it and reflash the app
    • then it prints the RAM address

Modify the layouts/raspberry_pi_pico.ld file and set the required addresses for the FLASH and RAM.

Extra

Implement the following extra features:

  1. Turn ON the Pi's LED if one of the doors is open
  2. Use button X to set and un set the smarthouse's alarm. The alarm will sound (blink the LED) when it is ON if one of the doors is open more than 10 seconds.