add board::delay

firmware/src/board/delay.rs

@@ -0,0 +1,76 @@
+use embedded_hal::blocking::delay::{DelayMs, DelayUs};
+use cortex_m::peripheral::syst::SystClkSource;
+use cortex_m::peripheral::SYST;
+use tm4c129x::CorePeripherals;
+
+/// precision internal oscillator
+const PIOSC: u32 = 16_000_000;
+
+pub struct Delay {
+    syst: SYST,
+}
+
+impl Delay {
+    pub fn new() -> Self {
+        let mut cp = unsafe { tm4c129x::CorePeripherals::steal() };
+        let mut syst = cp.SYST;
+        // PIOSC
+        syst.set_clock_source(SystClkSource::External);
+        syst.disable_interrupt();
+        Delay { syst }
+    }
+}
+
+impl DelayMs<u32> for Delay {
+    fn delay_ms(&mut self, ms: u32) {
+        self.delay_us(ms * 1_000);
+    }
+}
+
+impl DelayMs<u16> for Delay {
+    fn delay_ms(&mut self, ms: u16) {
+        self.delay_ms(u32::from(ms));
+    }
+}
+
+impl DelayMs<u8> for Delay {
+    fn delay_ms(&mut self, ms: u8) {
+        self.delay_ms(u32::from(ms));
+    }
+}
+
+impl DelayUs<u32> for Delay {
+    fn delay_us(&mut self, us: u32) {
+        // The SysTick Reload Value register supports values between 1 and 0x00FFFFFF.
+        const MAX_RVR: u32 = 0x00FF_FFFF;
+
+        let mut total_rvr = us * (PIOSC / 1_000_000);
+
+        while total_rvr != 0 {
+            let current_rvr = total_rvr.min(MAX_RVR);
+
+            self.syst.set_reload(current_rvr);
+            self.syst.clear_current();
+            self.syst.enable_counter();
+
+            // Update the tracking variable while we are waiting...
+            total_rvr -= current_rvr;
+
+            while !self.syst.has_wrapped() {}
+
+            self.syst.disable_counter();
+        }
+    }
+}
+
+impl DelayUs<u16> for Delay {
+    fn delay_us(&mut self, us: u16) {
+        self.delay_us(u32::from(us))
+    }
+}
+
+impl DelayUs<u8> for Delay {
+    fn delay_us(&mut self, us: u8) {
+        self.delay_us(u32::from(us))
+    }
+}

firmware/src/board/mod.rs

@@ -3,6 +3,7 @@ use tm4c129x;
 
 mod gpio;
 mod softspi;
+mod delay;
 
 
 const LED1: u8 = 0x10; // PK4