systick: use mutex

firmware/Cargo.lock

@@ -128,6 +128,7 @@ dependencies = [
 name = "ionpak-firmware"
 version = "1.0.0"
 dependencies = [
+ "bare-metal 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bit_field 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "cortex-m 0.5.10 (registry+https://github.com/rust-lang/crates.io-index)",

firmware/Cargo.toml

@@ -18,6 +18,7 @@ nb = "0.1"
 cortex-m-semihosting = "0.3"
 byteorder = { version = "1.3", default-features = false }
 bit_field = "0.10"
+bare-metal = "0.2"
 
 [dependencies.smoltcp]
 git = "https://github.com/m-labs/smoltcp"

firmware/src/board/mod.rs

@@ -9,7 +9,7 @@ pub mod systick;
 const UART_DIV: u32 = (((/*sysclk*/120_000_000 * 8) / /*baud*/115200) + 1) / 2;
 
 pub fn init() {
-    cortex_m::interrupt::free(|_cs| {
+    cortex_m::interrupt::free(|cs| {
         let sysctl = unsafe { &*tm4c129x::SYSCTL::ptr() };
 
         // Set up main oscillator
@@ -170,7 +170,7 @@ pub fn init() {
         setup_timer_pwm!(TIMER4);
         setup_timer_pwm!(TIMER5);
 
-        systick::init();
+        systick::init(cs);
     });
 }
 

firmware/src/board/systick.rs

@@ -1,16 +1,17 @@
-use cortex_m_rt::exception;
+use core::cell::RefCell;
+use cortex_m::interrupt::Mutex;
 use cortex_m::peripheral::{SYST, syst::SystClkSource};
+use cortex_m_rt::exception;
+use bare_metal::CriticalSection;
 
-const SYSTICK_RATE: u32 = 1000;
+const SYSTICK_RATE: u32 = 250;
 
-static mut TIME: u64 = 0;
+static mut TIME: Mutex<RefCell<u64>> = Mutex::new(RefCell::new(0));
 
-pub fn init() {
+pub fn init(cs: &CriticalSection) {
-    unsafe { TIME = 0 };
-    
     #[allow(mutable_transmutes)]
     let syst: &mut SYST = unsafe { core::mem::transmute(&*SYST::ptr()) };
-    syst.set_clock_source(SystClkSource::Core);
+    syst.set_clock_source(SystClkSource::External);
     syst.set_reload(100 * SYST::get_ticks_per_10ms() / SYSTICK_RATE);
     syst.clear_current();
     syst.enable_interrupt();
@@ -19,9 +20,14 @@ pub fn init() {
 
 #[exception]
 unsafe fn SysTick() {
-    TIME += u64::from(1000 / SYSTICK_RATE);
+    let interval = u64::from(1000 / SYSTICK_RATE);
+    cortex_m::interrupt::free(|cs| {
+        TIME.borrow(cs).replace_with(|time| *time + interval);
+    });
 }
 
 pub fn get_time() -> u64 {
-    unsafe { TIME }
+    cortex_m::interrupt::free(|cs| {
+        *unsafe { &mut TIME }.borrow(cs).borrow()
+    })
 }