examples/tcp_stm32f407.rs: Replace CYCCNT software timer with SysTick

Author: HarryMakes

examples/tcp_stm32f407.rs

@@ -31,7 +31,47 @@ use smoltcp::socket::{SocketSet, TcpSocket, TcpSocketBuffer};
 use core::str;
 use core::fmt::Write;
 
-use rtic::cyccnt::{Duration, Instant};
+/// Timer
+use core::cell::RefCell;
+use cortex_m::interrupt::Mutex;
+use cortex_m_rt::exception;
+use stm32f4xx_hal::{
+    rcc::Clocks,
+    time::MilliSeconds,
+    timer::{Timer, Event as TimerEvent},
+    stm32::SYST,
+};
+use smoltcp::time::{Instant, Duration};
+/// Rate in Hz
+const TIMER_RATE: u32 = 20;
+/// Interval duration in milliseconds
+const TIMER_DELTA: u32 = 1000 / TIMER_RATE;
+/// Elapsed time in milliseconds
+static TIMER_MS: Mutex<RefCell<u32>> = Mutex::new(RefCell::new(0));
+
+/// Setup SysTick exception
+fn timer_setup(syst: SYST, clocks: Clocks) {
+    let mut timer = Timer::syst(syst, TIMER_RATE.hz(), clocks);
+    timer.listen(TimerEvent::TimeOut);
+}
+
+/// SysTick exception (Timer)
+#[exception]
+fn SysTick() {
+    cortex_m::interrupt::free(|cs| {
+        *TIMER_MS.borrow(cs)
+            .borrow_mut() += TIMER_DELTA;
+    });
+}
+
+/// Obtain current time in milliseconds
+pub fn timer_now() -> MilliSeconds {
+    let ms = cortex_m::interrupt::free(|cs| {
+        *TIMER_MS.borrow(cs)
+            .borrow()
+    });
+    ms.ms()
+}
 
 ///
 use stm32f4xx_hal::{
@@ -89,6 +129,11 @@ const APP: () = {
         // Init ITM
         let mut itm = c.core.ITM;
         let stim0 = &mut itm.stim[0];
+        
+        // Setup SysTick
+        // Reference to stm32-eth:examples/ip.rs
+        timer_setup(c.core.SYST, clocks);
+        iprintln!(stim0, "Timer initialised.");
 
         // NIC100 / ENC424J600 Set-up
         let spi1 = c.device.SPI1;
@@ -149,6 +194,9 @@ const APP: () = {
                     .finalize()
             };
 
+            iprintln!(stim0, 
+                "Ethernet initialization complete");
+
             eth_iface
         };
 
@@ -163,9 +211,6 @@ const APP: () = {
         let stim0 = &mut c.resources.itm.stim[0];
         let mut iface = c.resources.eth_iface;
 
-        iprintln!(stim0, 
-            "Ethernet initialization complete");
-
         // Copied / modified from smoltcp:
         // examples/loopback.rs
         let echo_socket = {
@@ -191,18 +236,10 @@ const APP: () = {
         // smoltcp:examples/loopback.rs, examples/server.rs;
         // stm32-eth:examples/ip.rs,
         // git.m-labs.hk/M-Labs/tnetplug
-        let mut time = 0u32;
-        let mut next_ms = Instant::now();
-        use rtic::cyccnt::U32Ext;
-        next_ms += 168_000_u32.cycles();
         loop {
             // Poll
-            let tick = Instant::now() > next_ms;
-            if tick {
-                next_ms += 168_000_u32.cycles();
-                time += 1;
-            }
-            let instant = smoltcp::time::Instant::from_millis(time as i64);
+            let now = timer_now().0;
+            let instant = Instant::from_millis(now as i64);
             match iface.poll(&mut socket_set, instant) {
                 Ok(_) => {
                 },