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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)]
#![feature(const_fn)]
#![feature(proc_macro)]
#![no_std]
#[macro_use(task)]
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: {
enabled: true,
priority: 1,
resources: [LOW, HIGH],
},
EXTI1: {
enabled: true,
priority: 2,
resources: [LOW],
},
EXTI2: {
enabled: true,
priority: 3,
resources: [HIGH],
},
},
}
fn init(_p: init::Peripherals, _r: init::Resources) {}
fn idle() -> ! {
// 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();
}
}
task!(EXTI0, exti0);
fn exti0(t: &mut Threshold, r: EXTI0::Resources) {
// because this task has a priority of 1 the preemption threshold is also 1
let mut low = r.LOW;
let mut high = r.HIGH;
// A
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
// just high enough to not race with task `exti1` for access to the
// `LOW` resource
// C
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
// E
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);
// F
rtfm::bkpt();
});
// upon leaving the critical section the preemption threshold drops to 2
// and `exti2` immediately preempts this task
// ~> exti2
});
// once again the preemption threshold drops to 1
// now the pending `exti1` can preempt this task
// ~> exti1
}
task!(EXTI1, exti1);
fn exti1(_t: &mut Threshold, _r: EXTI1::Resources) {
// B, H
rtfm::bkpt();
}
task!(EXTI2, exti2);
fn exti2(_t: &mut Threshold, _r: EXTI2::Resources) {
// D, G
rtfm::bkpt();
}
|
