capsules_core/virtualizers/virtual_alarm.rs
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// Licensed under the Apache License, Version 2.0 or the MIT License.
// SPDX-License-Identifier: Apache-2.0 OR MIT
// Copyright Tock Contributors 2022.
//! Virtualize the Alarm interface to enable multiple users of an underlying
//! alarm hardware peripheral.
use core::cell::Cell;
use kernel::collections::list::{List, ListLink, ListNode};
use kernel::hil::time::{self, Alarm, Ticks, Time};
use kernel::utilities::cells::OptionalCell;
use kernel::ErrorCode;
#[derive(Copy, Clone)]
struct TickDtReference<T: Ticks> {
/// Reference time point when this alarm was setup.
reference: T,
/// Duration of this alarm w.r.t. the reference time point. In other words, this alarm should
/// fire at `reference + dt`.
dt: T,
/// True if this dt only represents a portion of the original dt that was requested. If true,
/// then we need to wait for another max_tick/2 after an internal extended dt reference alarm
/// fires. This ensures we can wait the full max_tick even if there is latency in the system.
extended: bool,
}
impl<T: Ticks> TickDtReference<T> {
#[inline]
fn reference_plus_dt(&self) -> T {
self.reference.wrapping_add(self.dt)
}
}
/// An object to multiplex multiple "virtual" alarms over a single underlying alarm. A
/// `VirtualMuxAlarm` is a node in a linked list of alarms that share the same underlying alarm.
pub struct VirtualMuxAlarm<'a, A: Alarm<'a>> {
/// Underlying alarm which multiplexes all these virtual alarm.
mux: &'a MuxAlarm<'a, A>,
/// Reference and dt point when this alarm was setup.
dt_reference: Cell<TickDtReference<A::Ticks>>,
/// Whether this alarm is currently armed, i.e. whether it should fire when the time has
/// elapsed.
armed: Cell<bool>,
/// Next alarm in the list.
next: ListLink<'a, VirtualMuxAlarm<'a, A>>,
/// Alarm client for this node in the list.
client: OptionalCell<&'a dyn time::AlarmClient>,
}
impl<'a, A: Alarm<'a>> ListNode<'a, VirtualMuxAlarm<'a, A>> for VirtualMuxAlarm<'a, A> {
fn next(&self) -> &'a ListLink<VirtualMuxAlarm<'a, A>> {
&self.next
}
}
impl<'a, A: Alarm<'a>> VirtualMuxAlarm<'a, A> {
/// After calling new, always call setup()
pub fn new(mux_alarm: &'a MuxAlarm<'a, A>) -> VirtualMuxAlarm<'a, A> {
let zero = A::Ticks::from(0);
VirtualMuxAlarm {
mux: mux_alarm,
dt_reference: Cell::new(TickDtReference {
reference: zero,
dt: zero,
extended: false,
}),
armed: Cell::new(false),
next: ListLink::empty(),
client: OptionalCell::empty(),
}
}
/// Call this method immediately after new() to link this to the mux, otherwise alarms won't
/// fire
pub fn setup(&'a self) {
self.mux.virtual_alarms.push_head(self);
}
}
impl<'a, A: Alarm<'a>> Time for VirtualMuxAlarm<'a, A> {
type Frequency = A::Frequency;
type Ticks = A::Ticks;
fn now(&self) -> Self::Ticks {
self.mux.alarm.now()
}
}
impl<'a, A: Alarm<'a>> Alarm<'a> for VirtualMuxAlarm<'a, A> {
fn set_alarm_client(&self, client: &'a dyn time::AlarmClient) {
self.client.set(client);
}
fn disarm(&self) -> Result<(), ErrorCode> {
if !self.armed.get() {
return Ok(());
}
self.armed.set(false);
let enabled = self.mux.enabled.get() - 1;
self.mux.enabled.set(enabled);
// If there are not more enabled alarms, disable the underlying alarm
// completely.
if enabled == 0 {
let _ = self.mux.alarm.disarm();
}
Ok(())
}
fn is_armed(&self) -> bool {
self.armed.get()
}
fn set_alarm(&self, reference: Self::Ticks, dt: Self::Ticks) {
let enabled = self.mux.enabled.get();
let half_max = Self::Ticks::half_max_value();
// If the dt is more than half of the available time resolution, then we need to break
// up the alarm into two internal alarms. This ensures that our internal comparisons of
// now outside of range [ref, ref + dt) will trigger correctly even with latency in the
// system
let dt_reference = if dt > half_max.wrapping_add(self.minimum_dt()) {
TickDtReference {
reference,
dt: dt.wrapping_sub(half_max),
extended: true,
}
} else {
TickDtReference {
reference,
dt,
extended: false,
}
};
self.dt_reference.set(dt_reference);
// Ensure local variable has correct value when used below
let dt = dt_reference.dt;
if !self.armed.get() {
self.mux.enabled.set(enabled + 1);
self.armed.set(true);
}
// First alarm, so set it
if enabled == 0 {
//debug!("virtual_alarm: first alarm: set it.");
self.mux.set_alarm(reference, dt);
} else if !self.mux.firing.get() {
// If firing is true, the mux will scan all the alarms after
// firing and pick the soonest one so do not need to modify the
// mux. Otherwise, this is an alarm
// started in a separate code path (e.g., another event).
// This new alarm fires sooner if two things are both true:
// 1. The current earliest alarm expiration doesn't fall
// in the range of [reference, reference+dt): this means
// it is either in the past (before reference) or the future
// (reference + dt), AND
// 2. now falls in the [reference, reference+dt)
// window of the current earliest alarm. This means the
// current earliest alarm hasn't fired yet (it is in the future).
// -pal
let cur_alarm = self.mux.alarm.get_alarm();
let now = self.mux.alarm.now();
let expiration = reference.wrapping_add(dt);
if !cur_alarm.within_range(reference, expiration) {
let next = self.mux.next_tick_vals.get();
if next.map_or(true, |(next_reference, next_dt)| {
now.within_range(next_reference, next_reference.wrapping_add(next_dt))
}) {
self.mux.set_alarm(reference, dt);
}
} else {
// current alarm will fire earlier, keep it
}
}
}
fn get_alarm(&self) -> Self::Ticks {
let dt_reference = self.dt_reference.get();
let extension = if dt_reference.extended {
Self::Ticks::half_max_value()
} else {
Self::Ticks::from(0)
};
dt_reference.reference_plus_dt().wrapping_add(extension)
}
fn minimum_dt(&self) -> Self::Ticks {
self.mux.alarm.minimum_dt()
}
}
impl<'a, A: Alarm<'a>> time::AlarmClient for VirtualMuxAlarm<'a, A> {
fn alarm(&self) {
self.client.map(|client| client.alarm());
}
}
/// Structure to control a set of virtual alarms multiplexed together on top of a single alarm.
pub struct MuxAlarm<'a, A: Alarm<'a>> {
/// Head of the linked list of virtual alarms multiplexed together.
virtual_alarms: List<'a, VirtualMuxAlarm<'a, A>>,
/// Number of virtual alarms that are currently enabled.
enabled: Cell<usize>,
/// Underlying alarm, over which the virtual alarms are multiplexed.
alarm: &'a A,
/// Whether we are firing; used to delay restarted alarms
firing: Cell<bool>,
/// Reference to next alarm
next_tick_vals: Cell<Option<(A::Ticks, A::Ticks)>>,
}
impl<'a, A: Alarm<'a>> MuxAlarm<'a, A> {
pub const fn new(alarm: &'a A) -> MuxAlarm<'a, A> {
MuxAlarm {
virtual_alarms: List::new(),
enabled: Cell::new(0),
alarm,
firing: Cell::new(false),
next_tick_vals: Cell::new(None),
}
}
pub fn set_alarm(&self, reference: A::Ticks, dt: A::Ticks) {
self.next_tick_vals.set(Some((reference, dt)));
self.alarm.set_alarm(reference, dt);
}
pub fn disarm(&self) {
self.next_tick_vals.set(None);
let _ = self.alarm.disarm();
}
}
impl<'a, A: Alarm<'a>> time::AlarmClient for MuxAlarm<'a, A> {
/// When the underlying alarm has fired, we have to multiplex this event back to the virtual
/// alarms that should now fire.
fn alarm(&self) {
// Check whether to fire each alarm. At this level, alarms are one-shot,
// so a repeating client will set it again in the alarm() callback.
self.firing.set(true);
self.virtual_alarms
.iter()
.filter(|cur| {
let dt_ref = cur.dt_reference.get();
// It is very important to get the current now time as the reference could have been
// set from now in the previous for_each iteration. We rely on the reference always
// being in the past when compared to now.
let now = self.alarm.now();
cur.armed.get() && !now.within_range(dt_ref.reference, dt_ref.reference_plus_dt())
})
.for_each(|cur| {
let dt_ref = cur.dt_reference.get();
if dt_ref.extended {
// The first part of the extended alarm just fired, leave alarm armed with
// remaining time.
cur.dt_reference.set(TickDtReference {
reference: dt_ref.reference_plus_dt(),
dt: A::Ticks::half_max_value(),
extended: false,
});
} else {
// Alarm fully expired, disarm and fire callback
cur.armed.set(false);
self.enabled.set(self.enabled.get() - 1);
//debug!(" Virtualizer: {:?} outside {:?}-{:?}, fire!", now, cur.reference.get(), cur.reference.get().wrapping_add(cur.dt.get()));
cur.alarm();
}
});
self.firing.set(false);
// Find the soonest alarm client (if any) and set the "next" underlying
// alarm based on it. This needs to happen after firing all expired
// alarms since those may have reset new alarms.
let now = self.alarm.now();
let next = self
.virtual_alarms
.iter()
.filter(|cur| cur.armed.get())
.min_by_key(|cur| {
let when = cur.dt_reference.get();
// If the alarm has already expired, then it should be
// considered as the earliest possible (0 ticks), so it
// will trigger as soon as possible. This can happen
// if the alarm expired *after* it was examined in the
// above loop.
if !now.within_range(when.reference, when.reference_plus_dt()) {
A::Ticks::from(0u32)
} else {
when.reference_plus_dt().wrapping_sub(now)
}
});
// Set the alarm.
if let Some(valrm) = next {
let dt_reference = valrm.dt_reference.get();
self.set_alarm(dt_reference.reference, dt_reference.dt);
} else {
self.disarm();
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use time::*;
struct FakeAlarm<'a> {
now: Cell<Ticks32>,
reference: Cell<Ticks32>,
dt: Cell<Ticks32>,
armed: Cell<bool>,
client: OptionalCell<&'a dyn AlarmClient>,
}
impl FakeAlarm<'_> {
fn new() -> Self {
Self {
now: Cell::new(1_000u32.into()),
reference: Cell::new(0u32.into()),
dt: Cell::new(0u32.into()),
armed: Cell::new(false),
client: OptionalCell::empty(),
}
}
/// The emulated delay from when hardware timer to when kernel loop will
/// run to check if alarms have fired or not.
pub fn hardware_delay(&self) -> Ticks32 {
Ticks32::from(10)
}
/// Fast forwards time to the next time we would fire an alarm and call client. Returns if
/// alarm is still armed after triggering client
pub fn trigger_next_alarm(&self) -> bool {
if !self.is_armed() {
return false;
}
self.now.set(
self.reference
.get()
.wrapping_add(self.dt.get())
.wrapping_add(self.hardware_delay()),
);
self.client.map(|c| c.alarm());
self.is_armed()
}
/// Runs for the specified number of ticks as long as there are alarms armed.
pub fn run_for_ticks(&self, left: Ticks32) {
let final_now = self.now.get().wrapping_add(left);
let mut left = left.into_u32();
while self.is_armed() {
// Ensure that we have enough remaining ticks to handle the next alarm. Reference is
// always in the past, so we need to figure out the difference between the reference
// and now to discount the DT the alarm needs to wait by.
let ticks_from_reference = self.now.get().wrapping_sub(self.reference.get());
let dt = self
.dt
.get()
.into_u32()
.saturating_sub(ticks_from_reference.into_u32());
if dt <= left {
left -= dt;
self.trigger_next_alarm();
} else {
break;
}
}
// Ensure that we ate up all of the time we were suppose to run for
self.now.set(final_now);
}
}
impl Time for FakeAlarm<'_> {
type Ticks = Ticks32;
type Frequency = Freq1KHz;
fn now(&self) -> Ticks32 {
// Every time we get now, it needs to increment to represent a free running timer
let new_now = Ticks32::from(self.now.get().into_u32() + 1);
self.now.set(new_now);
new_now
}
}
impl<'a> Alarm<'a> for FakeAlarm<'a> {
fn set_alarm_client(&self, client: &'a dyn AlarmClient) {
self.client.set(client);
}
fn set_alarm(&self, reference: Self::Ticks, dt: Self::Ticks) {
self.reference.set(reference);
self.dt.set(dt);
self.armed.set(true);
}
fn get_alarm(&self) -> Self::Ticks {
self.reference.get().wrapping_add(self.dt.get())
}
fn disarm(&self) -> Result<(), ErrorCode> {
self.armed.set(false);
Ok(())
}
fn is_armed(&self) -> bool {
self.armed.get()
}
fn minimum_dt(&self) -> Self::Ticks {
0u32.into()
}
}
struct ClientCounter(Cell<usize>);
impl ClientCounter {
fn new() -> Self {
Self(Cell::new(0))
}
fn count(&self) -> usize {
self.0.get()
}
}
impl AlarmClient for ClientCounter {
fn alarm(&self) {
self.0.set(self.0.get() + 1);
}
}
fn run_until_disarmed(alarm: &FakeAlarm) {
// Don't loop forever if we never disarm
for _ in 0..20 {
if !alarm.trigger_next_alarm() {
return;
}
}
}
#[test]
fn test_single_max_ticks_dt() {
let alarm = FakeAlarm::new();
let client = ClientCounter::new();
let dt = u32::MAX.into();
let mux = MuxAlarm::new(&alarm);
alarm.set_alarm_client(&mux);
let valarm = VirtualMuxAlarm::new(&mux);
valarm.setup();
valarm.set_alarm_client(&client);
valarm.set_alarm(valarm.now(), dt);
run_until_disarmed(&alarm);
assert_eq!(client.count(), 1);
}
#[test]
fn test_multiple_max_ticks_dt() {
let alarm = FakeAlarm::new();
let client = ClientCounter::new();
let dt = u32::MAX.into();
let mux = MuxAlarm::new(&alarm);
alarm.set_alarm_client(&mux);
let v_alarms = &[
VirtualMuxAlarm::new(&mux),
VirtualMuxAlarm::new(&mux),
VirtualMuxAlarm::new(&mux),
];
for (i, v) in v_alarms.iter().enumerate() {
v.setup();
v.set_alarm_client(&client);
// Start with reference in the past since fake alarm now start with 1000 as now()
v.set_alarm((i as u32).into(), dt);
}
run_until_disarmed(&alarm);
assert_eq!(client.count(), 3);
}
struct SetAlarmClient<'a> {
alarm: &'a VirtualMuxAlarm<'a, FakeAlarm<'a>>,
dt: u32,
}
impl<'a> SetAlarmClient<'a> {
fn new(alarm: &'a VirtualMuxAlarm<'a, FakeAlarm<'a>>, dt: u32) -> Self {
Self { alarm, dt }
}
}
impl AlarmClient for SetAlarmClient<'_> {
fn alarm(&self) {
self.alarm.set_alarm(self.alarm.now(), self.dt.into());
}
}
#[test]
fn test_second_alarm_set_during_first_alarm_firing() {
let alarm = FakeAlarm::new();
let mux = MuxAlarm::new(&alarm);
alarm.set_alarm_client(&mux);
// It is important that 0 is setup last so it is first in the linked list
let v_alarms = &[VirtualMuxAlarm::new(&mux), VirtualMuxAlarm::new(&mux)];
v_alarms[1].setup();
v_alarms[0].setup();
let set_v1_alarm = SetAlarmClient::new(&v_alarms[1], 100);
v_alarms[0].set_alarm_client(&set_v1_alarm);
let counter = ClientCounter::new();
v_alarms[1].set_alarm_client(&counter);
// Set the first alarm for 10 ticks in the future. This should then set the second alarm,
// but not call fired for the second alarm until the timer gets to 100
v_alarms[0].set_alarm(0.into(), 10.into());
let still_armed = alarm.trigger_next_alarm();
// Second alarm should not have triggered yet
assert!(alarm.now().into_u32() < 100);
assert_eq!(counter.count(), 0);
assert!(still_armed);
let still_armed = alarm.trigger_next_alarm();
assert!(alarm.now().into_u32() > 100);
assert_eq!(counter.count(), 1);
assert!(!still_armed);
}
#[test]
fn test_quick_alarms_not_skipped() {
let alarm = FakeAlarm::new();
let client = ClientCounter::new();
let mux = MuxAlarm::new(&alarm);
alarm.set_alarm_client(&mux);
let v_alarms = &[
VirtualMuxAlarm::new(&mux),
VirtualMuxAlarm::new(&mux),
VirtualMuxAlarm::new(&mux),
VirtualMuxAlarm::new(&mux),
VirtualMuxAlarm::new(&mux),
VirtualMuxAlarm::new(&mux),
];
// Precalculated the now and dt for all alarms. The DT should be large enough that the
// initial check for firing is not true, but after evaluating all alarms, they would all
// be firing. This happens since time "progresses" every time now() is called, which
// emulates the clock progressing in real time.
let now = alarm.now();
let dt = alarm
.hardware_delay()
.wrapping_add(Ticks32::from(v_alarms.len() as u32));
for v in v_alarms {
v.setup();
v.set_alarm_client(&client);
v.set_alarm(now, dt);
}
// Set one alarm to trigger immediately (at the hardware delay) and the other alarm to
// trigger in the future by some large degree
v_alarms[0].set_alarm(now, 0.into());
v_alarms[1].set_alarm(now, 1_000.into());
// Run the alarm long enough for every alarm but the longer alarm to fire, and all other
// alarms should have fired once
alarm.run_for_ticks(Ticks32::from(750));
assert_eq!(client.count(), v_alarms.len() - 1);
// Run the alarm long enough for the longer alarm to fire as well and verify count
alarm.run_for_ticks(Ticks32::from(750));
assert_eq!(client.count(), v_alarms.len());
}
}