How do you use the state pattern to manage the different states and transitions of your device driver?

Natively this pattern is common even without OOP for the embedded devices. Or you are solving low power quest, or boot sequence - in any case, there is a state pattern. One other name - is a state machine, it is a more common name from electronics design and FPGA. So just the nature of an electronic device.

// State interface class TrafficLightState { public: virtual void handle() = 0; }; // Concrete state classes class RedState : public TrafficLightState { public: void handle() override { std::cout << "Traffic Light is RED - STOP!\n"; } }; class GreenState : public TrafficLightState ..... class YellowState : public TrafficLightState ..... // Context class class TrafficLight { private: std::unique_ptr<TrafficLightState> currentState; public: TrafficLight() : currentState(std::make_unique<RedState>()) {} void changeState(std::unique_ptr<TrafficLightState> newState) { currentState = std::move(newState); } void request() { currentState->handle(); } };

extensibility and flexibility are the main cases, agree. One more - clarity of the code. By separating states your visual component of the class interface - easy to understand and as a result less errors with the usage of such a class will be.

I have used the state pattern in firmware development to handle the various states a device could be in such as unprovisioned, provisioning, connecting to wifi, provisioned, etc. The main benefit I've seen is it creates a very clear separation in the code of what happens in each state and how states transition. The code is very readable and, due to the pattern, separated in a way that makes it easy to reason about.

One of the challenges I've run into is having states that aren't clearly defined. For the pattern to work well you need very clear states and transitions. Once states try to do too much or you have too many of them the complexity will quickly become unmanageable and difficult to maintain.

I will add - that the biggest challenge is correctly apply this pattern, as described before only states covered by the proposed implementation, and nothing about the transitions ;) for the driver, not commonly but in some cases, you shall provide handling of transitions, and looks like an additional pattern shall be used - like a "transaction". But be aware - you need to design states properly if you are willing to handle transitions. Real life and best practice are fare from each other.

unfortunately, I have seen C driver solutions instead of C++, Linux, FreeRtos, and MbedOS - full of drivers written in LL language, but state patterns built in many of them. It looks rather different, and states have split the functionality set in an old-fashioned way, dirty and simple but clear and robust (state switch cases, of for the specific cases binary if-then tree style).