OO Library to handle Pico PIO relative interrupts: intro

RE: OO Library to handle Pico PIO relative interrupts: intro

Jan Cumps — Wed, 27 Aug 2025 13:41:04 GMT

How to use the library, with example: OO Library to handle Pico PIO relative interrupts: usage and example

RE: OO Library to handle Pico PIO relative interrupts: intro

DAB — Tue, 26 Aug 2025 19:00:12 GMT

Great solution to the problem Jan.

RE: OO Library to handle Pico PIO relative interrupts: intro

Jan Cumps — Mon, 25 Aug 2025 19:51:42 GMT

All 12 available PIO state machines on a Pico2 having all their PIO relative interrupts managed by their own object:

This is captured on a RISCV core. It works the same on the ARMs

RE: OO Library to handle Pico PIO relative interrupts: intro

Jan Cumps — Mon, 25 Aug 2025 15:26:00 GMT

Early results:

The mechanism works. A single class with 2 public methods supports the mechanism.

One to tell that we're interested in managing an interrupt. The other to register the object that will handle the interrupt.

The screen capture shows a minimal handler, that just prints a message and counts how many times it's been invoked.
The only requirement for a handler class is that it has line 15. All other implementation parts are for demo use.

RE: OO Library to handle Pico PIO relative interrupts: intro

Jan Cumps — Sun, 24 Aug 2025 19:58:25 GMT

C++ has a mechanism to enforce that a class has to provide particular operations. This allows to only accept classes and objects that can do a particular thing, without the need for a base class. And without inheritance.

In the lib that I'm writing, it's expected that the objects you pass to it for interrupt handling, can actually be executed. They need to provide the () operator.

C++ has concepts. Guards that you can use to investigate capabilities at compile time. There are standard ones, and you can define your own checks.

In this case, I'm lucky, because there is a standard concept to check if a template type can be executed: std::invocable. If I set that as a requirement for a template parameter, the code will not compile if you use the template class with a type that doesn't have the () operator:

[embed:dc8ab71f-3b98-42d9-b0f6-e21e02a0f8e2:35c030e2-a539-48b3-98e6-664149393e90:type=csharp&text=%2F%2F%20guard%20that%20E%20has%20to%20support%20%28%29%20operator.%0D%0Atemplate%20%3Cstd%3A%3Ainvocable%20E%2C%20uint32_t%20interrupt_number%3E%20class%20pio_irq%20%7B]

This is a help to the user of the library. They get a clear message that they are using the library with objects that aren't fit to handle the interrupts.

The nice thing is that E can actually be a simple function pointer. Doesn't need to be a class with () operator.

Another nice thing is that the runtime cost is zero.

RE: OO Library to handle Pico PIO relative interrupts: intro

shabaz — Sun, 24 Aug 2025 12:28:36 GMT

Looking forward to this! And it's becoming more relevant since number of PIO are increasing in each RPxxxx chip generation it seems. It will remove a bit of the 'wild west' when it comes to developing with them, when there are decent libraries to help with these common tasks.