72 MHz clock (HSE+PLL), timer experiments

src/main.rs

@@ -14,7 +14,7 @@ use panic_halt as _;
 use nb::block;
 
 use cortex_m_rt::entry;
-use stm32f1xx_hal::{pac, prelude::*, timer::Timer};
+use stm32f1xx_hal::{pac, prelude::*, rcc::Config, timer::Timer};
 
 #[entry]
 fn main() -> ! {
@@ -30,7 +30,20 @@ fn main() -> ! {
 
     // Freeze the configuration of all the clocks in the system and store the frozen frequencies in
     // `clocks`
-    let clocks = rcc.cfgr.freeze(&mut flash.acr);
+    let clocks = rcc.cfgr.freeze_with_config(
+        Config {
+            // HSE frequency
+            hse: Some(8_000_000),
+            // PLLMUL represented by an integer -2
+            pllmul: Some(9 - 2),
+            // PCLK1 freq must be 36 MHz or less
+            ppre1: stm32f1xx_hal::rcc::PPre::Div2,
+            // ADCCLK freq must be 14 MHz or less
+            adcpre: pac::rcc::cfgr::ADCPRE_A::Div6,
+            ..Default::default()
+        },
+        &mut flash.acr,
+    );
 
     // Acquire the GPIOC peripheral
     let mut gpioc = dp.GPIOC.split();
@@ -38,15 +51,27 @@ fn main() -> ! {
     // Configure gpio C pin 13 as a push-pull output. The `crh` register is passed to the function
     // in order to configure the port. For pins 0-7, crl should be passed instead.
     let mut led = gpioc.pc13.into_push_pull_output(&mut gpioc.crh);
+
     // Configure the syst timer to trigger an update every second
     let mut timer = Timer::syst(cp.SYST, &clocks).counter_hz();
-    timer.start(1.Hz()).unwrap();
+    // at 72 MHz, timer of 1 Hz overflows, use 10 Hz instead (8 Hz experimental minimum)
+    timer.start(10.Hz()).unwrap();
+
+    // equivalent timers:
+    // let mut timer = Timer::syst(cp.SYST, &clocks).counter_us(); // us resolution
+    // let mut timer: SysCounter<1000> = Timer::syst(cp.SYST, &clocks).counter(); // ms resolution
+    // timer.start(100.millis()).unwrap();
 
     // Wait for the timer to trigger an update and change the state of the LED
     loop {
+        for _ in 0..10 {
             block!(timer.wait()).unwrap();
+        }
         led.set_high();
+
+        for _ in 0..10 {
             block!(timer.wait()).unwrap();
+        }
         led.set_low();
     }
 }