proto_activities

Uses the protothreads approach to enable imperative synchronous programming (as promoted by Blech) in C or C++.

With this header-only library you can simplify your embedded programming projects by keeping a delay based approach but still enable multiple things to happen at once in a structured, modular and deterministic way.

Example code

/* This blinks an LED on every other tick. */
pa_activity (FastBlinker, pa_ctx(pa_defer_res), int pin) {
    pa_defer {
        setLED(pin, BLACK);
    };
    while (true) {
        setLED(pin, RED);
        pa_pause;

        setLED(pin, BLACK);
        pa_pause;
    }
} pa_end

/* This blinks an LED on a custom schedule. */
pa_activity (SlowBlinker, pa_ctx_tm(pa_defer_res), int pin, unsigned on_ticks, unsigned off_ticks) {
    pa_defer {
        setLED(pin, BLACK);
    };
    while (true) {
        setLED(pin, RED);
        pa_delay (on_ticks);

        setLED(pin, BLACK);
        pa_delay (off_ticks);
    }
} pa_end

/* An activity which delays for a given number of ticks. */
pa_activity (Delay, pa_ctx_tm(), unsigned ticks) {
    pa_delay (ticks);
} pa_end


/* This drives blinking LEDs and preempts them after 3 and 10 ticks. */
pa_activity (Main, pa_ctx_tm(pa_co_res(3); pa_use(Delay); pa_use(FastBlinker); pa_use(SlowBlinker))) {
    printf("Begin\n");

    /* Blink Fast LED for 3 ticks */
    pa_after_abort (3, FastBlinker, 0);
    
    /* Blink both LED for 10 ticks */
    pa_co(3) {
        pa_with (Delay, 10);
        pa_with_weak (FastBlinker, 0);
        pa_with_weak (SlowBlinker, 1, 3, 2);
    } pa_co_end
    
    printf("Done\n");
} pa_end

In this example, a fast led is blinked for 3 ticks and then both the fast and a slow led are blinked concurrently for 10 ticks.

Constructs

As can be seen in the example above, an activity is defined by the pa_activity macro which takes the name of the activity as first parameter.

This is followed by what is called a context (pa_ctx(...)) and which stores the state which should outlive a single tick. Also sub-activities used in the activity are declared here with the pa_use(<SomeActivity>) macro. Separate context elements need to be separated by a semicolon (;). To use delays within an activity, use pa_ctx_tm instead of pa_ctx, which holds an implicit time variable.

After the context, place the input and output parameters of the activity.

At the end of an activity, use pa_activity_end or just pa_end to close it off.

Within an activity you can place normal C control structures and the following synchronous statements.

For a detailed description of the statements, please currently refer to the Blech documentation or look at the proto_activities test and example programs.

• pa_pause: will pause processing of an activity and resume it at the next tick
• pa_halt: will pause the activity forever
• pa_await (cond): will pause the activity and resume it once cond becomes true
• pa_await_immediate (cond): like pa_await but will not pause if cond is true in the current tick
• pa_delay (ticks): will pause the activity for the given number of ticks
• pa_delay_ms (ms): will pause the activity for the given number of milliseconds
• pa_run (activity, ...): runs the given sub-activity until it returns
• pa_return: end an activity from within its body - otherwise returns implicitly at the end
• pa_co(n): starts a concurrent section with n trails - reserve the number of trails with pa_co_res(num_trails) in the activities context - end section with pa_co_end
• pa_with (activity, ...): runs the given activity concurrently with the others of this section - only applicable within pa_co
• pa_with_weak (activity, ...): runs the given activity concurrently with the others of this section and can be preempted - only applicable within pa_co
• pa_when_abort (cond, activity, ...): runs the given activity until cond becomes true in a subsequent tick - unless it ends before
• pa_when_reset (cond, activity, ...): runs the given activity and restarts it when cond becomes true in a subsequent tick
• pa_when_suspend (cond, activity, ...): will suspend the given activity while cond is true and lets it continue when cond is false again
• pa_after_abort (ticks, activity, ...): will abort the given activity after the specified number of ticks
• pa_after_ms_abort (ms, activity, ...): will abort the given activity after the specified time in milliseconds
• pa_did_abort (activity): reports whether an activity was aborted in a call before
• pa_always: will run code on every tick - end block with pa_always_end
• pa_every (cond): will run code everytime cond is true - end block with pa_every_end
• pa_every_ms (ms): will run code now and every ms milliseconds thereafter - end block with pa_every_end. Note: Do not use any other construct which uses timing (like pa_delay_ms) in the enclosed block
• pa_whenever (cond, activity, ...): will run the given activity whenever cond is true and abort it if cond turns false

When compiling wit C++ you could also define the following lifecycle callbacks:

• pa_defer: defines an instantaneous block of code to run when the activity ends by itself or gets aborted. Add pa_defer_res annotation to the context to enable this feature.
• pa_suspend: defines an instantaneous block of code to run when an activity gets suspended by the surrounding pa_when_suspend. Add pa_susres_res annotation to the context to enable this feature.
• pa_resume: defines an instantaneous block of code to run when an activity gets resumed by the surrounding pa_when_suspend. Add pa_susres_res annotation to the context to enable this feature.

Related projects

• A medium article about proto_activities can be found here.
• Here is a little robot with proto_activities running on three ESP32 nodes.
• See running proto_activities code in this online Wokwi simulator.
• Blech is a new programming language for the embedded domain which inspired proto_activities.
• Pappe is a sibling project which uses an embedded DSL to allow Blech-style imperative synchronous programming in Swift.