1 files changed, 99 insertions, 0 deletions
diff --git a/src/hpet.rs b/src/hpet.rs
new file mode 100644
index 0000000..6360486
--- /dev/null
+++ b/src/hpet.rs
@@ -0,0 +1,99 @@
+use crate::{
+    address::RawGenericAddress,
+    sdt::{SdtHeader, Signature},
+    AcpiError,
+    AcpiHandler,
+    AcpiTable,
+    AcpiTables,
+};
+use bit_field::BitField;
+
+#[derive(Debug)]
+pub enum PageProtection {
+    None,
+    /// Access to the rest of the 4KiB, relative to the base address, will not generate a fault.
+    Protected4K,
+    /// Access to the rest of the 64KiB, relative to the base address, will not generate a fault.
+    Protected64K,
+    Other,
+}
+
+/// Information about the High Precision Event Timer (HPET)
+#[derive(Debug)]
+pub struct HpetInfo {
+    // TODO(3.0.0): unpack these fields directly, and get rid of methods
+    pub event_timer_block_id: u32,
+    pub base_address: usize,
+    pub hpet_number: u8,
+    /// The minimum number of clock ticks that can be set without losing interrupts (for timers in Periodic Mode)
+    pub clock_tick_unit: u16,
+    pub page_protection: PageProtection,
+}
+
+impl HpetInfo {
+    pub fn new<H>(tables: &AcpiTables<H>) -> Result<HpetInfo, AcpiError>
+    where
+        H: AcpiHandler,
+    {
+        let hpet = tables.find_table::<HpetTable>()?;
+
+        // Make sure the HPET is in system memory
+        assert_eq!(hpet.base_address.address_space, 0);
+
+        Ok(HpetInfo {
+            event_timer_block_id: hpet.event_timer_block_id,
+            base_address: hpet.base_address.address as usize,
+            hpet_number: hpet.hpet_number,
+            clock_tick_unit: hpet.clock_tick_unit,
+            page_protection: match hpet.page_protection_and_oem.get_bits(0..4) {
+                0 => PageProtection::None,
+                1 => PageProtection::Protected4K,
+                2 => PageProtection::Protected64K,
+                3..=15 => PageProtection::Other,
+                _ => unreachable!(),
+            },
+        })
+    }
+
+    pub fn hardware_rev(&self) -> u8 {
+        self.event_timer_block_id.get_bits(0..8) as u8
+    }
+
+    pub fn num_comparators(&self) -> u8 {
+        self.event_timer_block_id.get_bits(8..13) as u8 + 1
+    }
+
+    pub fn main_counter_is_64bits(&self) -> bool {
+        self.event_timer_block_id.get_bit(13)
+    }
+
+    pub fn legacy_irq_capable(&self) -> bool {
+        self.event_timer_block_id.get_bit(15)
+    }
+
+    pub fn pci_vendor_id(&self) -> u16 {
+        self.event_timer_block_id.get_bits(16..32) as u16
+    }
+}
+
+#[repr(C, packed)]
+#[derive(Debug, Clone, Copy)]
+pub struct HpetTable {
+    /// The contents of the HPET's 'General Capabilities and ID register'
+    header: SdtHeader,
+    event_timer_block_id: u32,
+    base_address: RawGenericAddress,
+    hpet_number: u8,
+    clock_tick_unit: u16,
+    /// Bits `0..4` specify the page protection guarantee. Bits `4..8` are reserved for OEM attributes.
+    page_protection_and_oem: u8,
+}
+
+/// ### Safety: Implementation properly represents a valid HPET table.
+unsafe impl AcpiTable for HpetTable {
+    const SIGNATURE: Signature = Signature::HPET;
+
+    fn header(&self) -> &SdtHeader {
+        &self.header
+    }
+}