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|
//! Nesting claims and how the preemption threshold works
//!
//! If you run this program you'll hit the breakpoints as indicated by the
//! letters in the comments: A, then B, then C, etc.
#![deny(unsafe_code)]
#![deny(warnings)]
#![feature(proc_macro)]
#![no_std]
extern crate cortex_m_rtfm as rtfm;
extern crate stm32f103xx;
use stm32f103xx::Interrupt;
use rtfm::{app, Resource, Threshold};
app! {
device: stm32f103xx,
resources: {
static LOW: u64 = 0;
static HIGH: u64 = 0;
},
tasks: {
EXTI0: {
path: exti0,
priority: 1,
resources: [LOW, HIGH],
},
EXTI1: {
path: exti1,
priority: 2,
resources: [LOW],
},
EXTI2: {
path: exti2,
priority: 3,
resources: [HIGH],
},
},
}
fn init(_p: init::Peripherals, _r: init::Resources) {}
fn idle() -> ! {
// A
rtfm::bkpt();
// Sets task `exti0` as pending
//
// Because `exti0` has higher priority than `idle` it will be executed
// immediately
rtfm::set_pending(Interrupt::EXTI0); // ~> exti0
loop {
rtfm::wfi();
}
}
#[allow(non_snake_case)]
fn exti0(
t: &mut Threshold,
EXTI0::Resources { mut LOW, mut HIGH }: EXTI0::Resources,
) {
// Because this task has a priority of 1 the preemption threshold `t` also
// starts at 1
// B
rtfm::bkpt();
// Because `exti1` has higher priority than `exti0` it can preempt it
rtfm::set_pending(Interrupt::EXTI1); // ~> exti1
// A claim creates a critical section
LOW.claim_mut(t, |_low, t| {
// This claim increases the preemption threshold to 2
//
// 2 is just high enough to not race with task `exti1` for access to the
// `LOW` resource
// D
rtfm::bkpt();
// Now `exti1` can't preempt this task because its priority is equal to
// the current preemption threshold
rtfm::set_pending(Interrupt::EXTI1);
// But `exti2` can, because its priority is higher than the current
// preemption threshold
rtfm::set_pending(Interrupt::EXTI2); // ~> exti2
// F
rtfm::bkpt();
// Claims can be nested
HIGH.claim_mut(t, |_high, _| {
// This claim increases the preemption threshold to 3
// Now `exti2` can't preempt this task
rtfm::set_pending(Interrupt::EXTI2);
// G
rtfm::bkpt();
});
// Upon leaving the critical section the preemption threshold drops back
// to 2 and `exti2` immediately preempts this task
// ~> exti2
});
// Once again the preemption threshold drops but this time to 1. Now the
// pending `exti1` task can preempt this task
// ~> exti1
}
fn exti1(_t: &mut Threshold, _r: EXTI1::Resources) {
// C, I
rtfm::bkpt();
}
fn exti2(_t: &mut Threshold, _r: EXTI2::Resources) {
// E, H
rtfm::bkpt();
}
|
