GlobalTimer: add timer start with interrupt

libboard_zynq/src/timer/global.rs

@@ -24,6 +24,43 @@ impl GlobalTimer {
     pub fn start() -> GlobalTimer {
         let mut regs = mpcore::RegisterBlock::mpcore();
         Self::reset(&mut regs);
+
+        // Start
+        regs.global_timer_control.write(
+            mpcore::GlobalTimerControl::zeroed()
+                .prescaler((Self::get_prescalar() - 1) as u8)
+                .auto_increment_mode(true)
+                .timer_enable(true)
+        );
+        GlobalTimer { regs }
+    }
+
+    // Get the timer with a reset and interrupt
+    pub fn start_with_interrupt(interrupt_period_us: u64) -> GlobalTimer {
+        let mut regs = mpcore::RegisterBlock::mpcore();
+        Self::reset(&mut regs);
+
+        let prescaler = Self::get_prescalar() as u64;
+        let clocks = Clocks::get();
+        let increment_val:u32 = (interrupt_period_us * clocks.cpu_3x2x() as u64  / (1_000_000 * (prescaler + 1))) as u32;
+        
+        // When auto-increment and comp enable bits are set, an IRQ is generated periodically
+        unsafe{
+            regs.auto_increment.write(increment_val);
+        }
+        
+        // Clear event flag
+        Self::clear_isr();
+        
+        // Start
+        regs.global_timer_control.write(
+            mpcore::GlobalTimerControl::zeroed()
+                .prescaler((prescaler - 1) as u8)
+                .auto_increment_mode(true)
+                .comp_enable(true)
+                .irq_enable(true)
+                .timer_enable(true)
+        );
         GlobalTimer { regs }
     }
 
@@ -40,21 +77,24 @@ impl GlobalTimer {
         regs.global_timer_counter1.write(
             mpcore::ValueRegister::zeroed()
         );
+    }
 
+    pub fn clear_isr(){
+        let regs = mpcore::RegisterBlock::mpcore();
+        regs.global_timer_interrupt_status.write(
+            mpcore::GlobalTimerInterruptStatusRegister::zeroed()
+            .event_flag(true)
+        );
+    }
+
+    fn get_prescalar() -> u32 {
         // find a prescaler value that matches CPU speed / 2 to us
         let clocks = Clocks::get();
         let mut prescaler = clocks.cpu_3x2x() / 1_000_000;
         while prescaler > 256 {
             prescaler /= 2;
         }
-
-        // Start
-        regs.global_timer_control.write(
-            mpcore::GlobalTimerControl::zeroed()
-                .prescaler((prescaler - 1) as u8)
-                .auto_increment_mode(true)
-                .timer_enable(true)
-        );
+        prescaler
     }
 
     /// read the raw counter value