From caac7009f6a707446d4dfb556d27d949eba568a8 Mon Sep 17 00:00:00 2001
From: Christian Egerer <christian.egerer@1acue.de>
Date: Fri, 12 Apr 2024 14:31:54 +0300
Subject: [PATCH 1/2] add option to set HSE bypass bit

---
 src/rcc.rs | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/rcc.rs b/src/rcc.rs
index 508270b7..57e0b9ab 100644
--- a/src/rcc.rs
+++ b/src/rcc.rs
@@ -22,6 +22,7 @@ impl RccExt for RCC {
         Rcc {
             cfgr: CFGR {
                 hse: None,
+                hse_bypass: false,
                 hclk: None,
                 pclk1: None,
                 pclk2: None,
@@ -110,6 +111,7 @@ const HSI: u32 = 8_000_000; // Hz
 #[derive(Debug, Default, PartialEq, Eq)]
 pub struct CFGR {
     hse: Option<u32>,
+    hse_bypass: bool,
     hclk: Option<u32>,
     pclk1: Option<u32>,
     pclk2: Option<u32>,
@@ -127,6 +129,20 @@ impl CFGR {
         self
     }
 
+    /// Bypasses the high-speed external oscillator and uses an external clock input on the OSC_IN
+    /// pin.
+    ///
+    /// For this configuration, the OSC_IN pin should be connected to a clock source with a
+    /// frequency specified in the call to use_hse(), and the OSC_OUT pin should not be connected.
+    ///
+    /// This function has no effect unless use_hse() is also called.
+    pub fn bypass_hse_oscillator(self) -> Self {
+        Self {
+            hse_bypass: true,
+            ..self
+        }
+    }
+
     /// Sets the desired frequency for the HCLK clock
     #[inline(always)]
     pub fn hclk(mut self, freq: Hertz) -> Self {
@@ -208,7 +224,12 @@ impl CFGR {
         if cfg.hse.is_some() {
             // enable HSE and wait for it to be ready
 
-            rcc.cr.modify(|_, w| w.hseon().set_bit());
+            rcc.cr.modify(|_, w| {
+                if cfg.hse_bypass {
+                    w.hsebyp().bypassed();
+                }
+                w.hseon().set_bit()
+            });
 
             while rcc.cr.read().hserdy().bit_is_clear() {}
         }
@@ -478,6 +499,7 @@ pub trait Reset: RccBus {
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub struct Config {
     pub hse: Option<u32>,
+    pub hse_bypass: bool,
     pub pllmul: Option<u8>,
     pub hpre: HPre,
     pub ppre1: PPre,
@@ -491,6 +513,7 @@ impl Default for Config {
     fn default() -> Self {
         Self {
             hse: None,
+            hse_bypass: false,
             pllmul: None,
             hpre: HPre::Div1,
             ppre1: PPre::Div1,
@@ -549,6 +572,7 @@ pub type AdcPre = rcc::cfgr::ADCPRE_A;
 impl Config {
     pub const fn from_cfgr(cfgr: CFGR) -> Self {
         let hse = cfgr.hse;
+        let hse_bypass = cfgr.hse_bypass;
         let pllsrcclk = if let Some(hse) = hse { hse } else { HSI / 2 };
 
         let pllmul = if let Some(sysclk) = cfgr.sysclk {
@@ -649,6 +673,7 @@ impl Config {
 
         Self {
             hse,
+            hse_bypass,
             pllmul: pllmul_bits,
             hpre: hpre_bits,
             ppre1: ppre1_bits,
@@ -730,6 +755,7 @@ fn rcc_config_usb() {
     let config = Config::from_cfgr(cfgr);
     let config_expected = Config {
         hse: Some(8_000_000),
+        hse_bypass: false,
         pllmul: Some(4),
         hpre: HPre::Div1,
         ppre1: PPre::Div2,

From c2dc3be5c735315291851e3357c4a4ce6343fa43 Mon Sep 17 00:00:00 2001
From: Christian Egerer <christian.egerer@1acue.de>
Date: Mon, 15 Apr 2024 10:22:30 +0300
Subject: [PATCH 2/2] Update CHANGELOG.md

---
 CHANGELOG.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ed11be36..8b1d43b7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Add dac
 - Fix flash error flag clearing
 
+### Added
+
+- Allow to set HSE bypass bit in `RCC` clock configuration register to use an external clock input on the `OSC_IN` pin
+
 ## [v0.10.0] - 2022-12-12
 
 - `Timer`: adds `get_interrupt` to `Timer`