stm32/rcc: add shared code for hsi48 with crs support.

embassy-stm32/src/rcc/hsi48.rs

@@ -0,0 +1,62 @@
+#![allow(unused)]
+
+use crate::pac::crs::vals::Syncsrc;
+use crate::pac::{CRS, RCC};
+use crate::rcc::sealed::RccPeripheral;
+use crate::time::Hertz;
+
+/// HSI48 speed
+pub const HSI48_FREQ: Hertz = Hertz(48_000_000);
+
+/// Configuration for the HSI48 clock
+#[derive(Clone, Copy, Debug)]
+pub struct Hsi48Config {
+    /// Enable CRS Sync from USB Start Of Frame (SOF) events.
+    /// Required if HSI48 is going to be used as USB clock.
+    ///
+    /// Other use cases of CRS are not supported yet.
+    pub sync_from_usb: bool,
+}
+
+impl Default for Hsi48Config {
+    fn default() -> Self {
+        Self { sync_from_usb: false }
+    }
+}
+
+pub(crate) fn init_hsi48(config: Hsi48Config) -> Hertz {
+    // Enable VREFINT reference for HSI48 oscillator
+    #[cfg(stm32l0)]
+    crate::pac::SYSCFG.cfgr3().modify(|w| {
+        w.set_enref_hsi48(true);
+        w.set_en_vrefint(true);
+    });
+
+    // Enable HSI48
+    #[cfg(not(any(stm32u5, stm32g0, stm32h5, stm32h7, stm32u5, stm32wba, stm32f0)))]
+    let r = RCC.crrcr();
+    #[cfg(any(stm32u5, stm32g0, stm32h5, stm32h7, stm32u5, stm32wba))]
+    let r = RCC.cr();
+    #[cfg(any(stm32f0))]
+    let r = RCC.cr2();
+
+    r.modify(|w| w.set_hsi48on(true));
+    while r.read().hsi48rdy() == false {}
+
+    if config.sync_from_usb {
+        crate::peripherals::CRS::enable_and_reset();
+
+        CRS.cfgr().modify(|w| {
+            w.set_syncsrc(Syncsrc::USB);
+        });
+
+        // These are the correct settings for standard USB operation. If other settings
+        // are needed there will need to be additional config options for the CRS.
+        crate::pac::CRS.cr().modify(|w| {
+            w.set_autotrimen(true);
+            w.set_cen(true);
+        });
+    }
+
+    HSI48_FREQ
+}