capsules_core/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.
//! Tock syscall driver capsule for Alarms, which issue callbacks when
//! a point in time has been reached.
use kernel::grant::{AllowRoCount, AllowRwCount, Grant, UpcallCount};
use kernel::hil::time::{self, Alarm, Ticks};
use kernel::syscall::{CommandReturn, SyscallDriver};
use kernel::{ErrorCode, ProcessId};
/// Syscall driver number.
use crate::driver;
pub const DRIVER_NUM: usize = driver::NUM::Alarm as usize;
#[derive(Copy, Clone, Debug)]
struct Expiration<T: Ticks> {
reference: T,
dt: T,
}
#[derive(Copy, Clone)]
pub struct AlarmData<T: Ticks> {
expiration: Option<Expiration<T>>,
}
const ALARM_CALLBACK_NUM: usize = 0;
const NUM_UPCALLS: u8 = 1;
impl<T: Ticks> Default for AlarmData<T> {
fn default() -> AlarmData<T> {
AlarmData { expiration: None }
}
}
pub struct AlarmDriver<'a, A: Alarm<'a>> {
alarm: &'a A,
app_alarms:
Grant<AlarmData<A::Ticks>, UpcallCount<NUM_UPCALLS>, AllowRoCount<0>, AllowRwCount<0>>,
}
impl<'a, A: Alarm<'a>> AlarmDriver<'a, A> {
pub const fn new(
alarm: &'a A,
grant: Grant<
AlarmData<A::Ticks>,
UpcallCount<NUM_UPCALLS>,
AllowRoCount<0>,
AllowRwCount<0>,
>,
) -> AlarmDriver<'a, A> {
AlarmDriver {
alarm,
app_alarms: grant,
}
}
/// Find the earliest [`Expiration`] from an iterator of expirations.
///
/// Each [`Expiration`] value is provided as a tuple, with
/// - `UD`: an additional user-data argument returned together with the
/// [`Expiration`], should it be the earliest, and
/// - `F`: a call-back function invoked when the [`Expiration`] has already
/// expired. The callback is porivded the expiration value and a reference
/// to its user-data.
///
/// Whether an [`Expiration`] has expired or not is determined with respect
/// to `now`. If `now` is in `[exp.reference; exp.reference + exp.dt)`, it
/// the [`Expiration`] has not yet expired.
///
/// An expired [`Expiration`] is not a candidate for "earliest" expiration.
/// This means that this function will return `Ok(None)` if it receives an
/// empty iterator, or all [`Expiration`]s have expired.
///
/// To stop iteration on any expired [`Expiration`], its callback can return
/// `Some(R)`. Then this function will return `Err(Expiration, UD, R)`.
/// This avoids consuming the entire iterator.
fn earliest_alarm<UD, R, F: FnOnce(Expiration<A::Ticks>, &UD) -> Option<R>>(
now: A::Ticks,
expirations: impl Iterator<Item = (Expiration<A::Ticks>, UD, F)>,
) -> Result<Option<(Expiration<A::Ticks>, UD)>, (Expiration<A::Ticks>, UD, R)> {
let mut earliest: Option<(Expiration<A::Ticks>, UD)> = None;
for (exp, ud, expired_handler) in expirations {
let Expiration {
reference: exp_ref,
dt: exp_dt,
} = exp;
// Pre-compute the absolute "end" time of this expiration (the
// point at which it should fire):
let exp_end = exp_ref.wrapping_add(exp_dt);
// If `now` is not within `[reference, reference + dt)`, this
// alarm has expired. Call the expired handler. If it returns
// false, stop here.
if !now.within_range(exp_ref, exp_end) {
let expired_handler_res = expired_handler(exp, &ud);
if let Some(retval) = expired_handler_res {
return Err((exp, ud, retval));
}
}
// `exp` has not yet expired. At this point we can assume that
// `now` is within `[exp_ref, exp_end)`. Check whether it will
// expire earlier than the current `earliest`:
match &earliest {
None => {
// Do not have an earliest expiration yet, set this
// expriation as earliest:
earliest = Some((exp, ud));
}
Some((
Expiration {
reference: earliest_ref,
dt: earliest_dt,
},
_,
)) => {
// As `now` is within `[ref, end)` for both timers, we
// can check which end time is closer to `now`. We thus
// first compute the end time for the current earliest
// alarm as well ...
let earliest_end = earliest_ref.wrapping_add(*earliest_dt);
// ... and then perform a wrapping_sub against `now` for
// both, checking which is smaller:
let exp_remain = exp_end.wrapping_sub(now);
let earliest_remain = earliest_end.wrapping_sub(now);
if exp_remain < earliest_remain {
// Our current exp expires earlier than earliest,
// replace it:
earliest = Some((exp, ud));
}
}
}
}
// We have computed earliest by iterating over all alarms, but have not
// found one that has already expired. As such return `false`:
Ok(earliest)
}
/// Re-arm the timer. This must be called in response to the underlying
/// timer firing, or the set of [`Expiration`]s changing. This will iterate
/// over all [`Expiration`]s and
///
/// - invoke upcalls for all expired app alarms, resetting them afterwards,
/// - re-arming the alarm for the next earliest [`Expiration`], or
/// - disarming the alarm if no unexpired [`Expiration`] is found.
fn process_rearm_or_callback(&self) {
// Ask the clock about a current reference once. This can incur a
// volatile read, and this may not be optimized if done in a loop:
let now = self.alarm.now();
let expired_handler = |expired: Expiration<A::Ticks>, process_id: &ProcessId| {
// This closure is run on every expired alarm, _after_ the `enter()`
// closure on the Grant iterator has returned. We are thus not
// risking reentrancy here.
// Enter the app's grant again:
let _ = self.app_alarms.enter(*process_id, |alarm_state, upcalls| {
// Reset this app's alarm:
alarm_state.expiration = None;
// Deliver the upcall:
upcalls
.schedule_upcall(
ALARM_CALLBACK_NUM,
(
now.into_u32_left_justified() as usize,
expired
.reference
.wrapping_add(expired.dt)
.into_u32_left_justified() as usize,
0,
),
)
.ok();
});
// Proceed iteration across expirations:
None::<()>
};
// Compute the earliest alarm, and invoke the `expired_handler` for
// every expired alarm. This will issue a callback and reset the alarms
// respectively.
let res = Self::earliest_alarm(
now,
// Pass an interator of all non-None expirations:
self.app_alarms.iter().filter_map(|app| {
let process_id = app.processid();
app.enter(|alarm_state, _upcalls| {
if let Some(exp) = alarm_state.expiration {
Some((exp, process_id, expired_handler))
} else {
None
}
})
}),
);
// Arm or disarm the alarm accordingly:
match res {
// No pending alarm, disarm:
Ok(None) => {
let _ = self.alarm.disarm();
}
// A future, non-expired alarm should fire:
Ok(Some((Expiration { reference, dt }, _))) => {
self.alarm.set_alarm(reference, dt);
}
// The expired closure has requested to stop iteration. This should
// be unreachable, and hence we panic:
Err((_, _, ())) => {
unreachable!();
}
}
}
fn rearm_u32_left_justified_expiration(
now: A::Ticks,
reference_u32: Option<u32>,
dt_u32: u32,
expiration: &mut Option<Expiration<A::Ticks>>,
) -> u32 {
let reference_unshifted = reference_u32.map(|ref_u32| ref_u32 >> A::Ticks::u32_padding());
// If the underlying timer is less than 32-bit wide, userspace is able
// to provide a finer `reference` and `dt` resolution than we can
// possibly represent in the kernel.
//
// We do not want to switch back to userspace *before* the timer
// fires. As such, when userspace gives us reference and ticks values
// with a precision unrepresentible using our Ticks object, we round
// `reference` down, and `dt` up (ensuring that the timer cannot fire
// earlier than requested).
let dt_unshifted = if let Some(reference_u32) = reference_u32 {
// Computing unshifted dt for a userspace alarm can
// underestimate dt in some cases where both reference and
// dt had low-order bits that are rounded off by
// unshifting. To ensure `dt` results in an actual
// expiration that is at least as long as the expected
// expiration in user space, compute unshifted dt from an
// unshifted expiration.
let expiration_shifted = reference_u32.wrapping_add(dt_u32);
let expiration_unshifted =
if expiration_shifted & ((1 << A::Ticks::u32_padding()) - 1) != 0 {
// By right-shifting, we would decrease the requested dt value,
// firing _before_ the time requested by userspace. Add one to
// compensate this:
(expiration_shifted >> A::Ticks::u32_padding()) + 1
} else {
expiration_shifted >> A::Ticks::u32_padding()
};
expiration_unshifted.wrapping_sub(reference_u32 >> A::Ticks::u32_padding())
} else if dt_u32 & ((1 << A::Ticks::u32_padding()) - 1) != 0 {
// By right-shifting, we would decrease the requested dt value,
// firing _before_ the time requested by userspace. Add one to
// compensate this:
(dt_u32 >> A::Ticks::u32_padding()) + 1
} else {
// dt does not need to be shifted *or* contains no lower bits
// unrepresentable in the kernel:
dt_u32 >> A::Ticks::u32_padding()
};
// For timers less than 32-bit wide, we do not have to handle a
// `reference + dt` overflow specially. This is because those timers are
// conveyed to us left-justified, and as such userspace would already
// have to take care of such overflow.
//
// However, we *may* need to handle overflow when the timer is *wider*
// than 32 bit. In this case, if `reference + dt` were to overflow, we
// need to rebase our reference on the full-width `now` time.
//
// If userspace didn't give us a reference, we can skip all of this and
// simply set the unshifted dt.
let new_exp = match (reference_unshifted, A::Ticks::width() > 32) {
(Some(userspace_reference_unshifted), true) => {
// We have a userspace reference and timer is wider than 32 bit.
//
// In this case, we need to check whether the lower 32 bits of the
// timer `reference` have already wrapped, compared to the reference
// provided by userspace:
if now.into_u32() < userspace_reference_unshifted {
// The lower 32-bit of reference are smaller than the userspace
// reference. This means that the full-width timer has had an
// increment in the upper bits. We thus set the full-width
// reference to the combination of the current upper timer bits
// *minus 1*, concatenated to the user-space provided bits.
//
// Because we don't know the integer type of the Ticks object
// (just that it's larger than a u32), we:
//
// 1. subtract a full `u32::MAX + 1` to incur a downward wrap,
// effectively subtracting `1` from the upper part,
// 2. subtract the lower `u32` bits from this value, setting
// those bits to zero,
// 3. adding back the userspace-provided reference.
// Build 1 << 32:
let bit33 = A::Ticks::from(0xffffffff).wrapping_add(A::Ticks::from(0x1));
// Perform step 1, subtracting 1 << 32:
let sub_1_upper = now.wrapping_sub(bit33);
// Perform step 2, setting first 32 bit to zero:
let sub_lower =
sub_1_upper.wrapping_sub(A::Ticks::from(sub_1_upper.into_u32()));
// Perform step 3, add back the userspace-provided reference:
let rebased_reference =
sub_lower.wrapping_add(A::Ticks::from(userspace_reference_unshifted));
// Finally, return the new expiration. We don't have to do
// anything special for `dt`, as it's relative:
Expiration {
reference: rebased_reference,
dt: A::Ticks::from(dt_unshifted),
}
} else {
// The lower 32-bit of reference are equal to or larger than the
// userspace reference. Thus we can rebase the reference,
// touching only the lower 32 bit, by:
//
// 1. subtract the lower `u32` bits from this value, setting
// those bits to zero,
// 2. adding back the userspace-provided reference.
// Perform step 1, setting first 32 bit to zero:
let sub_lower = now.wrapping_sub(A::Ticks::from(now.into_u32()));
// Perform step 2, add back the userspace-provided reference:
let rebased_reference =
sub_lower.wrapping_add(A::Ticks::from(userspace_reference_unshifted));
// Finally, return the new expiration. We don't have to do
// anything special for `dt`, as it's relative:
Expiration {
reference: rebased_reference,
dt: A::Ticks::from(dt_unshifted),
}
}
}
(Some(userspace_reference_unshifted), false) => {
// We have a userspace reference and timer is (less than) 32
// bit. Simply set to unshifted values:
Expiration {
reference: A::Ticks::from(userspace_reference_unshifted),
dt: A::Ticks::from(dt_unshifted),
}
}
(None, _) => {
// We have no userspace reference. Use `now` as a reference:
Expiration {
reference: now,
dt: A::Ticks::from(dt_unshifted),
}
}
};
// Store the new expiration. We already adjusted the armed count above:
*expiration = Some(new_exp);
// Return the time left-justified time at which the alarm will fire:
new_exp
.reference
.wrapping_add(new_exp.dt)
.into_u32_left_justified()
}
}
impl<'a, A: Alarm<'a>> SyscallDriver for AlarmDriver<'a, A> {
/// Setup and read the alarm.
///
/// ### `command_num`
///
/// - `0`: Driver existence check.
/// - `1`: Return the clock frequency in Hz.
/// - `2`: Read the current clock value
/// - `3`: Stop the alarm if it is outstanding
/// - `4`: Deprecated
/// - `5`: Set an alarm to fire at a given clock value `time` relative to `now`
/// - `6`: Set an alarm to fire at a given clock value `time` relative to a provided
/// reference point.
fn command(
&self,
cmd_type: usize,
data: usize,
data2: usize,
caller_id: ProcessId,
) -> CommandReturn {
// Returns the error code to return to the user and whether we need to
// reset which is the next active alarm. We _don't_ reset if
// - we're disabling the underlying alarm anyway,
// - the underlying alarm is currently disabled and we're enabling the first alarm, or
// - on an error (i.e. no change to the alarms).
self.app_alarms
.enter(caller_id, |td, _upcalls| {
let now = self.alarm.now();
match cmd_type {
// Driver check:
//
// Don't re-arm the timer:
0 => (CommandReturn::success(), false),
1 => {
// Get clock frequency. We return a frequency scaled by
// the amount of padding we add to the `ticks` value
// returned in command 2 ("capture time"), such that
// userspace knows when the timer will wrap and can
// accurately determine the duration of a single tick.
//
// Don't re-arm the timer:
let scaled_freq =
<A::Ticks>::u32_left_justified_scale_freq::<A::Frequency>();
(CommandReturn::success_u32(scaled_freq), false)
}
2 => {
// Capture time. We pad the underlying timer's ticks to
// wrap at exactly `(2 ** 32) - 1`. This predictable
// wrapping value allows userspace to build long running
// timers beyond `2 ** now.width()` ticks.
//
// Don't re-arm the timer:
(
CommandReturn::success_u32(now.into_u32_left_justified()),
false,
)
}
3 => {
// Stop
match td.expiration {
None => {
// Request to stop when already stopped. Don't
// re-arm the timer:
(CommandReturn::failure(ErrorCode::ALREADY), false)
}
Some(_old_expiraton) => {
// Clear the expiration:
td.expiration = None;
// Ask for the timer to be re-armed. We can't do
// this here, as it would re-enter the grant
// region:
(CommandReturn::success(), true)
}
}
}
4 => {
// Deprecated in 2.0, used to be: set absolute expiration
//
// Don't re-arm the timer:
(CommandReturn::failure(ErrorCode::NOSUPPORT), false)
}
5 => {
// Set relative expiration.
//
// We provided userspace a potentially padded version of
// our in-kernel Ticks object, and as such we have to
// invert that operation through a right shift.
//
// Also, we need to keep track of the currently armed
// timers.
//
// All of this is done in the following helper method:
let new_exp_left_justified = Self::rearm_u32_left_justified_expiration(
// Current time:
now,
// No userspace-provided reference:
None,
// Left-justified `dt` value:
data as u32,
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut td.expiration,
);
// Report success, with the left-justified time at which
// the alarm will fire. Also ask for the timer to be
// re-armed. We can't do this here, as it would re-enter
// the grant region:
(CommandReturn::success_u32(new_exp_left_justified), true)
}
6 => {
// Also, we need to keep track of the currently armed
// timers.
//
// All of this is done in the following helper method:
let new_exp_left_justified = Self::rearm_u32_left_justified_expiration(
// Current time:
now,
// Left-justified userspace-provided reference:
Some(data as u32),
// Left-justified `dt` value:
data2 as u32,
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut td.expiration,
);
// Report success, with the left-justified time at which
// the alarm will fire. Also ask for the timer to be
// re-armed. We can't do this here, as it would re-enter
// the grant region:
(CommandReturn::success_u32(new_exp_left_justified), true)
}
// Unknown command:
//
// Don't re-arm the timer:
_ => (CommandReturn::failure(ErrorCode::NOSUPPORT), false),
}
})
.map_or_else(
|err| CommandReturn::failure(err.into()),
|(retval, rearm_timer)| {
if rearm_timer {
self.process_rearm_or_callback();
}
retval
},
)
}
fn allocate_grant(&self, processid: ProcessId) -> Result<(), kernel::process::Error> {
self.app_alarms.enter(processid, |_, _| {})
}
}
impl<'a, A: Alarm<'a>> time::AlarmClient for AlarmDriver<'a, A> {
fn alarm(&self) {
self.process_rearm_or_callback();
}
}
#[cfg(test)]
mod test {
use core::cell::Cell;
use core::marker::PhantomData;
use kernel::hil::time::{
Alarm, AlarmClient, Freq10MHz, Frequency, Ticks, Ticks24, Ticks32, Ticks64, Time,
};
use kernel::utilities::cells::OptionalCell;
use kernel::ErrorCode;
use super::{AlarmDriver, Expiration};
struct MockAlarm<'a, T: Ticks, F: Frequency> {
current_ticks: Cell<T>,
client: OptionalCell<&'a dyn AlarmClient>,
_frequency: PhantomData<F>,
}
impl<T: Ticks, F: Frequency> Time for MockAlarm<'_, T, F> {
type Frequency = F;
type Ticks = T;
fn now(&self) -> Self::Ticks {
self.current_ticks.get()
}
}
impl<'a, T: Ticks, F: Frequency> Alarm<'a> for MockAlarm<'a, T, F> {
fn set_alarm_client(&self, client: &'a dyn AlarmClient) {
self.client.set(client);
}
fn set_alarm(&self, _reference: Self::Ticks, _dt: Self::Ticks) {
unimplemented!()
}
fn get_alarm(&self) -> Self::Ticks {
unimplemented!()
}
fn disarm(&self) -> Result<(), ErrorCode> {
unimplemented!()
}
fn is_armed(&self) -> bool {
unimplemented!()
}
fn minimum_dt(&self) -> Self::Ticks {
unimplemented!()
}
}
#[test]
fn test_earliest_alarm_no_alarms() {
assert!(
AlarmDriver::<MockAlarm<Ticks32, Freq10MHz>>::earliest_alarm(
// Now:
Ticks32::from(42_u32),
// Expirations:
<[(
Expiration<kernel::hil::time::Ticks32>,
(),
fn(_, &()) -> Option<()>
); 0] as IntoIterator>::into_iter([])
)
.unwrap()
.is_none()
)
}
#[test]
fn test_earliest_alarm_multiple_unexpired() {
// Should never be called:
let exp_handler = |exp, id: &usize| -> Option<()> {
panic!("Alarm should not be expired: {:?}, id: {}", exp, id)
};
let (earliest, id) = AlarmDriver::<MockAlarm<Ticks32, Freq10MHz>>::earliest_alarm(
// Now:
42_u32.into(),
// Expirations:
[
(
// Will expire at 52:
Expiration {
reference: 42_u32.into(),
dt: 10_u32.into(),
},
0,
exp_handler,
),
(
// Will expire at exactly 43:
Expiration {
reference: u32::MAX.into(),
dt: 44_u32.into(),
},
1,
exp_handler,
),
(
// Will expire at 44:
Expiration {
reference: 10_u32.into(),
dt: 34_u32.into(),
},
2,
exp_handler,
),
]
.into_iter(),
)
.unwrap()
.unwrap();
assert!(earliest.reference.into_u32() == u32::MAX);
assert!(earliest.dt.into_u32() == 44);
assert!(id == 1);
}
#[test]
fn test_earliest_alarm_multiple_expired() {
let exp_list: [Cell<bool>; 7] = Default::default();
let exp_handler = |_exp, id: &usize| -> Option<()> {
exp_list[*id].set(true);
// Don't stop iterating on the first expired alarm:
None
};
let (earliest, id) = AlarmDriver::<MockAlarm<Ticks32, Freq10MHz>>::earliest_alarm(
// Now:
42_u32.into(),
// Expirations:
[
(
// Has expired at 42 (current cycle), should fire!
Expiration {
reference: 41_u32.into(),
dt: 1_u32.into(),
},
0,
&exp_handler,
),
(
// Will expire at 52, should not fire.
Expiration {
reference: 42_u32.into(),
dt: 10_u32.into(),
},
1,
&exp_handler,
),
(
// Will expire at exactly 43, should not fire.
Expiration {
reference: u32::MAX.into(),
dt: 44_u32.into(),
},
2,
&exp_handler,
),
(
// Reference is current time, expiration in the future,
// should not fire:
Expiration {
reference: 42_u32.into(),
dt: 1_u32.into(),
},
3,
&exp_handler,
),
(
// Reference is 43 (current time + 1), interpreted as "in
// the past", should fire:
Expiration {
reference: 43_u32.into(),
dt: 1_u32.into(),
},
4,
&exp_handler,
),
(
// Reference is 0, end is at 1, in the past, should fire:
Expiration {
reference: 0_u32.into(),
dt: 1_u32.into(),
},
5,
&exp_handler,
),
(
// Reference is u32::MAX, end is at 0, in the past, should fire:
Expiration {
reference: u32::MAX.into(),
dt: 1_u32.into(),
},
6,
&exp_handler,
),
]
.into_iter(),
)
.unwrap()
.unwrap();
assert!(earliest.reference.into_u32() == 41);
assert!(earliest.dt.into_u32() == 1);
assert!(id == 0);
let mut bool_exp_list: [bool; 7] = [false; 7];
exp_list
.into_iter()
.zip(bool_exp_list.iter_mut())
.for_each(|(src, dst)| *dst = src.get());
assert!(bool_exp_list == [true, false, false, false, true, true, true]);
}
#[test]
fn test_earliest_alarm_expired_stop() {
let exp_list: [Cell<bool>; 4] = Default::default();
let exp_handler = |_exp, id: &usize| -> Option<&'static str> {
exp_list[*id].set(true);
// Stop iterating on id == 3
if *id == 3 {
Some("stopped")
} else {
None
}
};
let (expired, id, expired_ret) =
AlarmDriver::<MockAlarm<Ticks32, Freq10MHz>>::earliest_alarm(
// Now:
42_u32.into(),
// Expirations:
[
(
// Will expire at 52, should not fire.
Expiration {
reference: 42_u32.into(),
dt: 10_u32.into(),
},
0,
&exp_handler,
),
(
// Has expired at 42 (current cycle), should fire!
Expiration {
reference: 41_u32.into(),
dt: 1_u32.into(),
},
1,
&exp_handler,
),
(
// Will expire at exactly 43, should not fire.
Expiration {
reference: u32::MAX.into(),
dt: 44_u32.into(),
},
2,
&exp_handler,
),
(
// Reference is 0, end is at 1, in the past, should fire:
Expiration {
reference: 0_u32.into(),
dt: 1_u32.into(),
},
3,
&exp_handler,
),
]
.into_iter(),
)
.err()
.unwrap();
assert!(expired.reference.into_u32() == 0);
assert!(expired.dt.into_u32() == 1);
assert!(id == 3);
assert!(expired_ret == "stopped");
let mut bool_exp_list: [bool; 4] = [false; 4];
exp_list
.into_iter()
.zip(bool_exp_list.iter_mut())
.for_each(|(src, dst)| *dst = src.get());
assert!(bool_exp_list == [false, true, false, true,]);
}
#[test]
fn test_rearm_24bit_left_justified_noref_basic() {
let mut expiration = None;
assert!(Ticks24::u32_padding() == 8);
let armed_time =
AlarmDriver::<MockAlarm<Ticks24, Freq10MHz>>::rearm_u32_left_justified_expiration(
// Current time:
Ticks24::from(1337_u32),
// No userspace-provided reference:
None,
// Left-justified `dt` value:
1234_u32 << Ticks24::u32_padding(),
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut expiration,
);
let expiration = expiration.unwrap();
assert_eq!(armed_time, (1337 + 1234) << Ticks24::u32_padding());
assert_eq!(expiration.reference.into_u32(), 1337);
assert_eq!(expiration.dt.into_u32(), 1234);
}
#[test]
fn test_rearm_24bit_left_justified_noref_wrapping() {
let mut expiration = None;
let armed_time =
AlarmDriver::<MockAlarm<Ticks24, Freq10MHz>>::rearm_u32_left_justified_expiration(
// Current time:
Ticks24::from(1337_u32),
// No userspace-provided reference:
None,
// Left-justified `dt` value (in this case, with some
// irrepresentable precision)
u32::MAX - (42 << Ticks24::u32_padding()),
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut expiration,
);
let expiration = expiration.unwrap();
// (1337 + ((0xffffffff - (42 << 8)) >> 8) + 1) % 0x01000000 = 1295
assert_eq!(armed_time, 1295 << Ticks24::u32_padding());
assert_eq!(expiration.reference.into_u32(), 1337);
assert_eq!(
expiration.dt.into_u32(),
// dt is rounded up to the next representable tick:
((u32::MAX - (42 << Ticks24::u32_padding())) >> Ticks24::u32_padding()) + 1
);
}
#[test]
fn test_rearm_24bit_left_justified_ref_low_bits_basic() {
let mut expiration = None;
assert!(Ticks24::u32_padding() == 8);
let armed_time =
AlarmDriver::<MockAlarm<Ticks24, Freq10MHz>>::rearm_u32_left_justified_expiration(
// Current time:
Ticks24::from(0_u32),
// Userspace-provided reference, below minimum precision of Ticks24, will be rounded down:
Some(1_u32),
// Left-justified `dt` value, below minimum precision of Ticks24, will be rounded up:
3_u32,
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut expiration,
);
let expiration = expiration.unwrap();
// ((1 >> 8) + ((3 >> 8) + 1) << 8) = 1
assert_eq!(armed_time, 1 << 8);
assert_eq!(expiration.reference.into_u32(), 0);
assert_eq!(expiration.dt.into_u32(), 1);
}
#[test]
fn test_rearm_24bit_left_justified_ref_low_bits_max_int() {
let mut expiration = None;
assert!(Ticks24::u32_padding() == 8);
let armed_time =
AlarmDriver::<MockAlarm<Ticks24, Freq10MHz>>::rearm_u32_left_justified_expiration(
// Current time:
Ticks24::from(6_u32),
// Userspace-provided reference, including bits not representable in Ticks24:
// (5 << 8) - 43 = 1237
Some(Ticks24::from(5_u32).into_u32_left_justified() - 43),
// Left-justified `dt` value, including bits not representable in Ticks24:
// (2 << 8) - 43 = 469
Ticks24::from(2_u32).into_u32_left_justified() + 43,
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut expiration,
);
let expiration = expiration.unwrap();
// When we naively round down reference `(1237 / 256 ~= 4.83 -> 4)` and
// round up dt `(469 / 256 ~= 1.83 -> 2)` we'd arm the alarm to
// `2 + 4 = 6`. However, when considering the full resolution
// `reference + dt` `(1237 + 256) / 256 ~= 6.67` we can see that arming
// to `6` will have the alarm fire too early. The alarm rearm code needs
// to compensate for the case that (reference + dt) overflow and generate
// a dt from that rounded value, in this case `7`.
assert_eq!(armed_time, 7 << 8);
assert_eq!(expiration.reference.into_u32(), 4);
assert_eq!(expiration.dt, Ticks24::from(3));
}
#[test]
fn test_rearm_32bit_left_justified_noref_basic() {
let mut expiration = Some(Expiration {
reference: 0_u32.into(),
dt: 1_u32.into(),
});
assert!(Ticks32::u32_padding() == 0);
let armed_time =
AlarmDriver::<MockAlarm<Ticks32, Freq10MHz>>::rearm_u32_left_justified_expiration(
// Current time:
Ticks32::from(1337_u32),
// No userspace-provided reference:
None,
// Left-justified `dt` value, unshifted for 32 bit:
1234_u32,
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut expiration,
);
let expiration = expiration.unwrap();
assert_eq!(armed_time, 1337 + 1234);
assert_eq!(expiration.reference.into_u32(), 1337);
assert_eq!(expiration.dt.into_u32(), 1234);
}
#[test]
fn test_rearm_32bit_left_justified_noref_wrapping() {
let mut expiration = None;
let armed_time =
AlarmDriver::<MockAlarm<Ticks32, Freq10MHz>>::rearm_u32_left_justified_expiration(
// Current time:
Ticks32::from(1337_u32),
// No userspace-provided reference:
None,
// Left-justified `dt` value (in this case, with some
// irrepresentable precision)
u32::MAX - 42,
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut expiration,
);
let expiration = expiration.unwrap();
// (1337 + (0xffffffff - 42)) % 0x100000000 = 1294
assert_eq!(armed_time, 1294);
assert_eq!(expiration.reference.into_u32(), 1337);
assert_eq!(expiration.dt.into_u32(), u32::MAX - 42);
}
#[test]
fn test_rearm_64bit_left_justified_noref_wrapping() {
let mut expiration = Some(Expiration {
reference: 0_u32.into(),
dt: 1_u32.into(),
});
assert!(Ticks64::u32_padding() == 0);
let armed_time =
AlarmDriver::<MockAlarm<Ticks64, Freq10MHz>>::rearm_u32_left_justified_expiration(
// Current time:
Ticks64::from(0xDEADBEEFCAFE_u64),
// No userspace-provided reference:
None,
// Left-justified `dt` value, unshifted for 32 bit:
0xDEADC0DE_u32,
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut expiration,
);
let expiration = expiration.unwrap();
assert_eq!(armed_time, 0x9D9D8BDC_u32);
assert_eq!(expiration.reference.into_u64(), 0xDEADBEEFCAFE_u64);
assert_eq!(expiration.dt.into_u64(), 0xDEADC0DE_u64);
}
#[test]
fn test_rearm_64bit_left_justified_refnowrap_dtnorwap() {
let mut expiration = None;
// reference smaller than now & 0xffffffff, reference + dt don't wrap:
let armed_time =
AlarmDriver::<MockAlarm<Ticks64, Freq10MHz>>::rearm_u32_left_justified_expiration(
// Current time:
Ticks64::from(0xDEADBEEFCAFE_u64),
// Userspace-provided reference, smaller than now and dt
Some(0xBEEFC0DE_u32),
// Left-justified `dt` value, unshifted for 32 bit:
0x1BADB002_u32,
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut expiration,
);
let expiration = expiration.unwrap();
assert_eq!(armed_time, 0xDA9D70E0_u32); // remains at 0xDEAD
assert_eq!(expiration.reference.into_u64(), 0xDEADBEEFC0DE_u64);
assert_eq!(expiration.dt.into_u64(), 0x1BADB002_u64);
}
#[test]
fn test_rearm_64bit_left_justified_refnowrwap_dtwrap() {
let mut expiration = Some(Expiration {
reference: 0_u32.into(),
dt: 1_u32.into(),
});
// reference smaller than now & 0xffffffff, reference + dt wrap:
let armed_time =
AlarmDriver::<MockAlarm<Ticks64, Freq10MHz>>::rearm_u32_left_justified_expiration(
// Current time:
Ticks64::from(0xDEADBEEFCAFE_u64),
// Userspace-provided reference, smaller than lower 32-bit of now
Some(0x8BADF00D_u32),
// Left-justified `dt` value, unshifted for 32 bit:
0xFEEDC0DE_u32,
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut expiration,
);
let expiration = expiration.unwrap();
assert_eq!(armed_time, 0x8A9BB0EB_u32); // wraps t0 0x0xDEAE
assert_eq!(expiration.reference.into_u64(), 0xDEAD8BADF00D_u64);
assert_eq!(expiration.dt.into_u64(), 0xFEEDC0DE_u64);
}
#[test]
fn test_rearm_64bit_left_justified_refwrap_dtwrap() {
let mut expiration = None;
// reference larger than now & 0xffffffff, reference + dt wrap:
let armed_time =
AlarmDriver::<MockAlarm<Ticks64, Freq10MHz>>::rearm_u32_left_justified_expiration(
// Current time:
Ticks64::from(0xDEADBEEFCAFE_u64),
// Userspace-provided reference, larger than lower 32-bit of
// now, meaning that it's already past:
Some(0xCAFEB0BA_u32),
// Left-justified `dt` value, unshifted for 32 bit:
0xFEEDC0DE_u32,
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut expiration,
);
let expiration = expiration.unwrap();
assert_eq!(armed_time, 0xC9EC7198_u32); // wraps to 0xDEAE
assert_eq!(expiration.reference.into_u64(), 0xDEACCAFEB0BA_u64);
assert_eq!(expiration.dt.into_u64(), 0xFEEDC0DE_u64);
}
#[test]
fn test_rearm_64bit_left_justified_refwrap_dtnowrap() {
let mut expiration = Some(Expiration {
reference: 0_u32.into(),
dt: 1_u32.into(),
});
// reference larger than now & 0xffffffff, reference + dt don't wrap
let armed_time =
AlarmDriver::<MockAlarm<Ticks64, Freq10MHz>>::rearm_u32_left_justified_expiration(
// Current time:
Ticks64::from(0xDEADBEEFCAFE_u64),
// Userspace-provided reference, larger than lower 32-bit of now
Some(0xCAFEB0BA_u32),
// Left-justified `dt` value, unshifted for 32 bit:
0x1BADB002_u32,
// Reference to the `Option<Expiration>`, also used
// to update the counter of armed alarms:
&mut expiration,
);
let expiration = expiration.unwrap();
assert_eq!(armed_time, 0xE6AC60BC_u32); // remains at 0xDEAD
assert_eq!(expiration.reference.into_u64(), 0xDEACCAFEB0BA_u64);
assert_eq!(expiration.dt.into_u64(), 0x1BADB002_u64);
}
}