Write hpet timer 0 twice to set accumulator and period

This allows booting with implementations that require them to be set separately.
Also, check for the availability of legacy-replacement mode and periodic interrupts before using hpet

src/arch/x86_64/device/hpet.rs

@@ -11,20 +11,39 @@ static CAPABILITY_OFFSET: usize = 0x00;
 static GENERAL_CONFIG_OFFSET: usize = 0x10;
 // static GENERAL_INTERRUPT_OFFSET: usize = 0x20;
 // static MAIN_COUNTER_OFFSET: usize = 0xF0;
+// static NUM_TIMER_CAP_MASK: u64 = 0x0f00;
+static LEG_RT_CAP: u64 = 0x8000;
 static T0_CONFIG_CAPABILITY_OFFSET: usize = 0x100;
 static T0_COMPARATOR_OFFSET: usize = 0x108;
 
-pub unsafe fn init(hpet: &mut Hpet) {
-    let counter_clk_period_fs = hpet.base_address.read_u64(CAPABILITY_OFFSET) >> 32;
+static PER_INT_CAP: u64 = 0x10;
+
+pub unsafe fn init(hpet: &mut Hpet) -> bool {
+    let capability = hpet.base_address.read_u64(CAPABILITY_OFFSET);
+    if capability & LEG_RT_CAP == 0 {
+        return false;
+    }
+
+    let counter_clk_period_fs = capability >> 32;
     let desired_fs_period: u64 = 2_250_286 * 1_000_000;
 
     let clk_periods_per_kernel_tick: u64 = desired_fs_period / counter_clk_period_fs;
 
-    let enable_word: u64 = hpet.base_address.read_u64(GENERAL_CONFIG_OFFSET) | LEG_RT_CNF | ENABLE_CNF;
-    hpet.base_address.write_u64(GENERAL_CONFIG_OFFSET, enable_word);
-    // Enable interrupts from the HPET
+    let t0_capabilities = hpet.base_address.read_u64(T0_CONFIG_CAPABILITY_OFFSET);
+    if t0_capabilities & PER_INT_CAP == 0 {
+        return false;
+    }
 
     let t0_config_word: u64 = TN_VAL_SET_CNF | TN_TYPE_CNF | TN_INT_ENB_CNF;
     hpet.base_address.write_u64(T0_CONFIG_CAPABILITY_OFFSET, t0_config_word);
     hpet.base_address.write_u64(T0_COMPARATOR_OFFSET, clk_periods_per_kernel_tick);
+    // set accumulator value
+    hpet.base_address.write_u64(T0_COMPARATOR_OFFSET, clk_periods_per_kernel_tick);
+    // set interval
+
+    let enable_word: u64 = hpet.base_address.read_u64(GENERAL_CONFIG_OFFSET) | LEG_RT_CNF | ENABLE_CNF;
+    hpet.base_address.write_u64(GENERAL_CONFIG_OFFSET, enable_word);
+    // Enable interrupts from the HPET
+
+    true
 }

src/arch/x86_64/device/mod.rs

@@ -16,9 +16,12 @@ pub unsafe fn init(active_table: &mut ActivePageTable){
 
 pub unsafe fn init_noncore() {
     {
-        if let Some(ref mut hpet) = *ACPI_TABLE.hpet.write() {
-            hpet::init(hpet);
+        let using_hpet = if let Some(ref mut hpet) = *ACPI_TABLE.hpet.write() {
+            hpet::init(hpet)
         } else {
+            false
+        };
+        if !using_hpet {
             pit::init();
         }
     }