feat(acpi): add an ACPI power management timer

alioth/src/arch/x86_64/layout.rs

@@ -70,6 +70,7 @@ pub const PORT_FW_CFG_DMA_LO: u16 = 0x518;
 pub const PORT_ACPI_SLEEP_CONTROL: u16 = 0x600;
 pub const PORT_ACPI_SLEEP_STATUS: u16 = 0x601;
 pub const PORT_ACPI_RESET: u16 = 0x604;
+pub const PORT_ACPI_TIMER: u16 = 0x608;
 
 pub const PORT_PCI_ADDRESS: u16 = 0xcf8;
 pub const PORT_PCI_DATA: u16 = 0xcfc;

alioth/src/board/board_x86_64/board_x86_64.rs

@@ -29,15 +29,15 @@ use zerocopy::{FromZeros, IntoBytes};
 use crate::arch::cpuid::CpuidIn;
 use crate::arch::layout::{
     BIOS_DATA_END, EBDA_END, EBDA_START, IOAPIC_START, MEM_64_START, PORT_ACPI_RESET,
-    PORT_ACPI_SLEEP_CONTROL, RAM_32_SIZE,
+    PORT_ACPI_SLEEP_CONTROL, PORT_ACPI_TIMER, RAM_32_SIZE,
 };
 use crate::arch::msr::{IA32_MISC_ENABLE, MiscEnable};
 use crate::board::{Board, BoardConfig, CpuTopology, PCIE_MMIO_64_SIZE, Result, VcpuGuard, error};
 use crate::device::ioapic::IoApic;
 use crate::firmware::acpi::bindings::{
     AcpiTableFadt, AcpiTableHeader, AcpiTableRsdp, AcpiTableXsdt3,
 };
-use crate::firmware::acpi::reg::{FadtReset, FadtSleepControl};
+use crate::firmware::acpi::reg::{AcpiPmTimer, FadtReset, FadtSleepControl};
 use crate::firmware::acpi::{
     AcpiTable, create_fadt, create_madt, create_mcfg, create_rsdp, create_xsdt,
 };
@@ -431,6 +431,7 @@ where
         let memory = &self.memory;
         memory.add_io_dev(PORT_ACPI_RESET, Arc::new(FadtReset))?;
         memory.add_io_dev(PORT_ACPI_SLEEP_CONTROL, Arc::new(FadtSleepControl))?;
+        memory.add_io_dev(PORT_ACPI_TIMER, Arc::new(AcpiPmTimer::new()))?;
         if self.config.coco.is_none() {
             let ram = memory.ram_bus();
             acpi_table.relocate(EBDA_START + size_of::<AcpiTableRsdp>() as u64);

alioth/src/firmware/acpi/acpi.rs

@@ -19,11 +19,12 @@ use std::mem::{offset_of, size_of};
 
 use zerocopy::{FromBytes, IntoBytes, transmute};
 
-use crate::arch::layout::PCIE_CONFIG_START;
 #[cfg(target_arch = "x86_64")]
 use crate::arch::layout::{
     APIC_START, IOAPIC_START, PORT_ACPI_RESET, PORT_ACPI_SLEEP_CONTROL, PORT_ACPI_SLEEP_STATUS,
 };
+use crate::arch::layout::{PCIE_CONFIG_START, PORT_ACPI_TIMER};
+use crate::firmware::acpi::bindings::AcpiFadtFlag;
 use crate::utils::wrapping_sum;
 
 use self::bindings::{
@@ -93,6 +94,13 @@ pub fn create_fadt(dsdt_addr: u64) -> AcpiTableFadt {
             address: transmute!(PORT_ACPI_RESET as u64),
         },
         reset_value: FADT_RESET_VAL,
+        xpm_timer_block: AcpiGenericAddress {
+            space_id: 1,
+            bit_width: 32,
+            bit_offset: 0,
+            access_width: 3,
+            address: transmute!(PORT_ACPI_TIMER as u64),
+        },
         sleep_control: AcpiGenericAddress {
             space_id: 1,
             bit_width: 8,
@@ -107,7 +115,9 @@ pub fn create_fadt(dsdt_addr: u64) -> AcpiTableFadt {
             access_width: 1,
             address: transmute!(PORT_ACPI_SLEEP_STATUS as u64),
         },
-        flags: (1 << 20) | (1 << 10),
+        flags: AcpiFadtFlag::HW_REDUCED_ACPI
+            | AcpiFadtFlag::RESET_REG_SUP
+            | AcpiFadtFlag::TMR_VAL_EXT,
         minor_revision: FADT_MINOR_VERSION,
         hypervisor_id: *b"ALIOTH  ",
         xdsdt: transmute!(dsdt_addr),

alioth/src/firmware/acpi/bindings.rs

@@ -13,7 +13,9 @@
 // limitations under the License.
 
 use bitfield::bitfield;
-use zerocopy::{FromBytes, Immutable, IntoBytes};
+use zerocopy::{FromBytes, Immutable, IntoBytes, KnownLayout};
+
+use crate::bitflags;
 
 pub const SIG_RSDP: [u8; 8] = *b"RSD PTR ";
 pub const SIG_XSDT: [u8; 4] = *b"XSDT";
@@ -82,6 +84,15 @@ pub struct AcpiGenericAddress {
 pub const FADT_MAJOR_VERSION: u8 = 6;
 pub const FADT_MINOR_VERSION: u8 = 4;
 
+bitflags! {
+    #[derive(Default, KnownLayout, Immutable, FromBytes, IntoBytes)]
+    pub struct AcpiFadtFlag(u32) {
+        TMR_VAL_EXT = 1 << 8;
+        RESET_REG_SUP = 1 << 10;
+        HW_REDUCED_ACPI = 1 << 20;
+    }
+}
+
 #[repr(C, align(4))]
 #[derive(Debug, Clone, Default, FromBytes, Immutable, IntoBytes)]
 pub struct AcpiTableFadt {
@@ -124,7 +135,7 @@ pub struct AcpiTableFadt {
     pub boot_flags: u8,
     pub boot_flags_hi: u8,
     pub reserved: u8,
-    pub flags: u32,
+    pub flags: AcpiFadtFlag,
     pub reset_register: AcpiGenericAddress,
     pub reset_value: u8,
     pub arm_boot_flags: u8,

alioth/src/firmware/acpi/reg.rs

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::time::Instant;
+
 use crate::firmware::acpi::bindings::FadtSleepControlReg;
 use crate::mem::Result;
 use crate::mem::emulated::{Action, Mmio};
@@ -60,3 +62,47 @@ impl Mmio for FadtSleepControl {
         }
     }
 }
+
+/// Power Management Timer
+///
+/// ACPI v6.5, Sec. 4.8.2.1
+#[derive(Debug)]
+pub struct AcpiPmTimer {
+    start: Instant,
+}
+
+const PM_TIMER_FREQUENCY_HZ: u128 = 3_579_545;
+
+impl AcpiPmTimer {
+    pub fn new() -> Self {
+        Self {
+            start: Instant::now(),
+        }
+    }
+}
+
+impl Default for AcpiPmTimer {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Mmio for AcpiPmTimer {
+    fn read(&self, _offset: u64, _size: u8) -> Result<u64> {
+        let nanos = Instant::now().duration_since(self.start).as_nanos();
+        let counter = nanos * PM_TIMER_FREQUENCY_HZ / 1_000_000_000;
+        Ok(counter as u32 as u64)
+    }
+
+    fn write(&self, _offset: u64, _size: u8, _val: u64) -> Result<Action> {
+        Ok(Action::None)
+    }
+
+    fn size(&self) -> u64 {
+        4
+    }
+}
+
+#[cfg(test)]
+#[path = "reg_test.rs"]
+mod tests;

alioth/src/firmware/acpi/reg_test.rs

@@ -0,0 +1,24 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use crate::firmware::acpi::reg::AcpiPmTimer;
+use crate::mem::emulated::Mmio;
+
+#[test]
+fn test_pm_timer() {
+    let timer = AcpiPmTimer::default();
+    let v1 = timer.read(0, 4).unwrap();
+    let v2 = timer.read(0, 4).unwrap();
+    assert!(v2 > v1);
+}