From bbcdae6703317022f9120d7fc589abe1563c6464 Mon Sep 17 00:00:00 2001
From: "bors[bot]" <26634292+bors[bot]@users.noreply.github.com>
Date: Wed, 29 Dec 2021 20:11:25 +0000
Subject: [PATCH] Merge #374

374: Construct a SysTick delay with a clock source r=adamgreig a=mciantyre

Helpful for users who prefer an external clock source for their system
timer. Proposing this as a 0.7 backwards-compatible change.

Co-authored-by: Ian McIntyre <ianpmcintyre@gmail.com>
---
 CHANGELOG.md |  2 ++
 src/delay.rs | 22 ++++++++++++++--------
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2e7d1e75..fdb8be9c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Added `DWT.set_cycle_count` (#347).
 - Added support for the Cortex-M7 TCM and cache access control registers.
   There is a feature `cm7` to enable access to these.
+- Added `delay::Delay::with_source`, a constructor that lets you specify
+  the SysTick clock source (#374).
 
 ### Deprecated
 
diff --git a/src/delay.rs b/src/delay.rs
index 8ed1fea0..66a63bf6 100644
--- a/src/delay.rs
+++ b/src/delay.rs
@@ -6,7 +6,7 @@ use embedded_hal::blocking::delay::{DelayMs, DelayUs};
 /// System timer (SysTick) as a delay provider.
 pub struct Delay {
     syst: SYST,
-    ahb_frequency: u32,
+    frequency: u32,
 }
 
 impl Delay {
@@ -14,13 +14,19 @@ impl Delay {
     ///
     /// `ahb_frequency` is a frequency of the AHB bus in Hz.
     #[inline]
-    pub fn new(mut syst: SYST, ahb_frequency: u32) -> Self {
-        syst.set_clock_source(SystClkSource::Core);
+    pub fn new(syst: SYST, ahb_frequency: u32) -> Self {
+        Self::with_source(syst, ahb_frequency, SystClkSource::Core)
+    }
 
-        Delay {
-            syst,
-            ahb_frequency,
-        }
+    /// Configures the system timer (SysTick) as a delay provider
+    /// with a clock source.
+    ///
+    /// `frequency` is the frequency of your `clock_source` in Hz.
+    #[inline]
+    pub fn with_source(mut syst: SYST, frequency: u32, clock_source: SystClkSource) -> Self {
+        syst.set_clock_source(clock_source);
+
+        Delay { syst, frequency }
     }
 
     /// Releases the system timer (SysTick) resource.
@@ -32,7 +38,7 @@ impl Delay {
     /// Delay using the Cortex-M systick for a certain duration, in µs.
     #[allow(clippy::missing_inline_in_public_items)]
     pub fn delay_us(&mut self, us: u32) {
-        let ticks = (u64::from(us)) * (u64::from(self.ahb_frequency)) / 1_000_000;
+        let ticks = (u64::from(us)) * (u64::from(self.frequency)) / 1_000_000;
 
         let full_cycles = ticks >> 24;
         if full_cycles > 0 {