libboard_zynq: add GlobalTimer::get_us(), use in libsupport_zynq::logger

experiments/src/main.rs

@@ -72,7 +72,7 @@ pub fn main_core0() {
     }
     let mut flash = flash.stop();
 
-    let timer = libboard_zynq::timer::GlobalTimer::new();
+    let timer = libboard_zynq::timer::GlobalTimer::start();
 
     let mut ddr = zynq::ddr::DdrRam::new();
     #[cfg(not(feature = "target_zc706"))]
@@ -268,7 +268,11 @@ pub fn main_core0() {
     task::spawn(async move {
         loop {
             delay(&mut countdown, Milliseconds(1000)).await;
-            println!("time: {} ms", timer.get_time().0);
+
+            let timestamp = timer.get_us();
+            let seconds   = timestamp / 1_000_000;
+            let micros    = timestamp % 1_000_000;
+            println!("time: {:6}.{:06}s", seconds, micros);
         }
     });
 

libboard_zynq/src/mpcore.rs

@@ -92,7 +92,7 @@ register!(value_register, ValueRegister, RW, u32);
 register_bits!(value_register, value, u32, 0, 31);
 
 register!(global_timer_control, GlobalTimerControl, RW, u32);
-register_bits!(global_timer_control, prescaler, u16, 8, 15);
+register_bits!(global_timer_control, prescaler, u8, 8, 15);
 register_bit!(global_timer_control, auto_increment_mode, 3);
 register_bit!(global_timer_control, irq_enable, 2);
 register_bit!(global_timer_control, comp_enablea, 1);

libboard_zynq/src/timer/global.rs

@@ -13,7 +13,14 @@ pub struct GlobalTimer {
 }
 
 impl GlobalTimer {
-    pub fn new() -> GlobalTimer {
+    /// Get the potentially uninitialized timer
+    pub unsafe fn get() -> GlobalTimer {
+        let mut regs = mpcore::RegisterBlock::new();
+        GlobalTimer { regs }
+    }
+
+    /// Get the timer with a reset
+    pub fn start() -> GlobalTimer {
         let mut regs = mpcore::RegisterBlock::new();
         Self::reset(&mut regs);
         GlobalTimer { regs }
@@ -33,12 +40,17 @@ impl GlobalTimer {
             mpcore::ValueRegister::zeroed()
         );
 
+        // 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()
-                // maximum prescaler is still enough for millisecond
-                // precision while overflowing after centuries.
-                .prescaler(255)
+                .prescaler((prescaler - 1) as u8)
                 .auto_increment_mode(true)
                 .timer_enable(true)
         );
@@ -66,6 +78,14 @@ impl GlobalTimer {
         Milliseconds(self.get_counter() * (prescaler + 1) / (clocks.cpu_3x2x() as u64 / 1000))
     }
 
+    /// read with high precision
+    pub fn get_us(&self) -> u64 {
+        let prescaler = self.regs.global_timer_control.read().prescaler() as u64;
+        let clocks = Clocks::get();
+
+        1_000_000 * self.get_counter() * (prescaler + 1) / clocks.cpu_3x2x() as u64
+    }
+
     /// return a handle that has implements
     /// `embedded_hal::timer::CountDown`
     pub fn countdown(&self) -> CountDown {

libsupport_zynq/src/logger.rs

@@ -1,6 +1,6 @@
 //! A logger for the `log` crate
 
-use libboard_zynq::{println, stdio};
+use libboard_zynq::{println, stdio, timer::GlobalTimer};
 
 pub static LOGGER: Logger = Logger;
 
@@ -17,8 +17,9 @@ impl log::Log for Logger {
 
     fn log(&self, record: &log::Record) {
         if self.enabled(record.metadata()) {
-            // TODO: let timestamp = clock::get_us();
-            let timestamp = 0;
+            let timestamp = unsafe {
+                GlobalTimer::get()
+            }.get_us();
             let seconds   = timestamp / 1_000_000;
             let micros    = timestamp % 1_000_000;