Jeremy Soller
50 lines
1.9 KiB
Rust
50 lines
1.9 KiB
Rust
#[cfg(feature = "acpi")]
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use super::device::hpet;
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use super::device::pit;
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pub fn monotonic_absolute() -> u128 {
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// The paravirtualized TSC is already guaranteed to be monotonic, and thus doesn't need to be
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// readjusted.
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#[cfg(feature = "x86_kvm_pv")]
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if let Some(ns) = super::device::tsc::monotonic_absolute() {
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return ns;
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}
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*crate::time::OFFSET.lock() + hpet_or_pit()
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}
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fn hpet_or_pit() -> u128 {
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#[cfg(feature = "acpi")]
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if let Some(ref hpet) = *crate::acpi::ACPI_TABLE.hpet.read() {
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//TODO: handle rollover?
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//TODO: improve performance
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// Current count
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let counter = unsafe { hpet.read_u64(hpet::MAIN_COUNTER_OFFSET) };
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// Comparator holds next interrupt count
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let comparator = unsafe { hpet.read_u64(hpet::T0_COMPARATOR_OFFSET) };
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// Get period in femtoseconds
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let capability = unsafe { hpet.read_u64(hpet::CAPABILITY_OFFSET) };
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// There seems to be a bug in qemu on macos that causes the calculation to produce 0 for
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// period_fs and hence a divide by zero calculating the divisor - workaround it while we
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// try and get a fix from qemu: https://gitlab.com/qemu-project/qemu/-/issues/1570
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let mut period_fs = capability >> 32;
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if period_fs == 0 {
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period_fs = 10_000_000;
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}
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// Calculate divisor
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let divisor = (pit::RATE as u64 * 1_000_000) / period_fs;
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// Calculate last interrupt
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let last_interrupt = comparator.saturating_sub(divisor);
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// Calculate ticks since last interrupt
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let elapsed = counter.saturating_sub(last_interrupt);
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// Calculate nanoseconds since last interrupt
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return (elapsed as u128 * period_fs as u128) / 1_000_000;
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}
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// Read ticks since last interrupt
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let elapsed = unsafe { pit::read() };
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// Calculate nanoseconds since last interrupt
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(elapsed as u128 * pit::PERIOD_FS) / 1_000_000
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}
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