From 2e358dea263b82c2a5d4f9b7d1236190666c1f37 Mon Sep 17 00:00:00 2001
From: Ryan Summers <ryan.summers@vertigo-designs.com>
Date: Tue, 9 Feb 2021 14:36:50 +0100
Subject: [PATCH] Adding support for input capture prefilter configuration

---
 src/hardware/digital_input_stamper.rs |  8 ++++----
 src/hardware/timers.rs                | 17 +++++++++++++++++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/src/hardware/digital_input_stamper.rs b/src/hardware/digital_input_stamper.rs
index cc764f5..baddeba 100644
--- a/src/hardware/digital_input_stamper.rs
+++ b/src/hardware/digital_input_stamper.rs
@@ -44,12 +44,12 @@ impl InputStamper {
     ) -> Self {
         // Utilize the TIM5 CH4 as an input capture channel - use TI4 (the DI0 input trigger) as the
         // capture source.
-        let input_capture =
+        let mut input_capture =
             timer_channel.into_input_capture(timers::tim5::CaptureSource4::TI4);
 
-        // FIXME: hack in de-glitching filter
-        let regs = unsafe { &*hal::stm32::TIM5::ptr() };
-        regs.ccmr2_input().modify(|_, w| w.ic4f().bits(0b0011));
+        // Do not prescale the input capture signal - require 8 consecutive samples to record an
+        // incoming event - this prevents spurious glitches from triggering captures.
+        input_capture.configure_filter(timers::InputFilter::Div1N8);
 
         Self {
             capture_channel: input_capture,
diff --git a/src/hardware/timers.rs b/src/hardware/timers.rs
index e2cbbc8..fe90677 100644
--- a/src/hardware/timers.rs
+++ b/src/hardware/timers.rs
@@ -48,6 +48,13 @@ pub enum SlaveMode {
     Trigger = 0b0110,
 }
 
+/// Optional input capture preconditioning filter configurations.
+#[allow(dead_code)]
+pub enum InputFilter {
+    Div1N1 = 0b0000,
+    Div1N8 = 0b0011,
+}
+
 macro_rules! timer_channels {
     ($name:ident, $TY:ident, $size:ty) => {
         paste::paste! {
@@ -334,6 +341,16 @@ macro_rules! timer_channels {
                     let regs = unsafe { &*<$TY>::ptr() };
                     regs.sr.read().[< cc $index of >]().bit_is_set()
                 }
+
+                /// Configure the input capture input pre-filter.
+                ///
+                /// # Args
+                /// * `filter` - The desired input filter stage configuration. Defaults to disabled.
+                #[allow(dead_code)]
+                pub fn configure_filter(&mut self, filter: super::InputFilter) {
+                    let regs = unsafe { &*<$TY>::ptr() };
+                    regs.[< $ccmrx _input >]().modify(|_, w| w.[< ic $index f >]().bits(filter as u8));
+                }
             }
 
             // Note(unsafe): This manually implements DMA support for input-capture channels. This