From 248f9fea2c2d7a3ce80a09538712a89b94615dbc Mon Sep 17 00:00:00 2001
From: Alastair Hughes <alastair.hughes@tomra.com>
Date: Thu, 8 May 2025 16:32:15 +0200
Subject: [PATCH] Fix hall sensor velocity estimation

The hall sensor velocity estimation could end up returning a nonzero
value if the timer "wrapped" between runs, even if the motor was
actually stationary. If using the velocity regulator the motor may then
fail to start.

To solve this:
- Switch to using unsigned types so that wrapping is defined.
- When timing out the pulse value, also reset it so that the velocity
  won't be briefly treated as valid again when the timer wraps.

Seen on a platform with 32 bit long, so running the motor and then
waiting ~40 minutes is enough to observe this bug.
Note that the pulse_diff variable is reset if the hall sensor direction
changes, which may happen naturally when the motor stops, depending on
what it is attached to.
---
 src/sensors/HallSensor.cpp | 15 ++++++++++++---
 src/sensors/HallSensor.h   |  2 +-
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/sensors/HallSensor.cpp b/src/sensors/HallSensor.cpp
index 38767d59..37730251 100644
--- a/src/sensors/HallSensor.cpp
+++ b/src/sensors/HallSensor.cpp
@@ -122,10 +122,19 @@ float HallSensor::getSensorAngle() {
 */
 float HallSensor::getVelocity(){
   noInterrupts();
-  long last_pulse_timestamp = pulse_timestamp;
-  long last_pulse_diff = pulse_diff;
+  unsigned long last_pulse_timestamp = pulse_timestamp;
+  unsigned long last_pulse_diff = pulse_diff;
   interrupts();
-  if (last_pulse_diff == 0 || ((long)(_micros() - last_pulse_timestamp) > last_pulse_diff*2) ) { // last velocity isn't accurate if too old
+  if (last_pulse_diff == 0) {
+    return 0;
+  } else if ((_micros() - last_pulse_timestamp) > last_pulse_diff*2) {
+    // Last velocity isn't accurate if too old.
+    // Reset to avoid the diff being used again when the time wraps.
+    noInterrupts();
+    if (pulse_diff == last_pulse_diff) {
+        pulse_diff = 0;
+    }
+    interrupts();
     return 0;
   } else {
     return direction * (_2PI / (float)cpr) / (last_pulse_diff / 1000000.0f);
diff --git a/src/sensors/HallSensor.h b/src/sensors/HallSensor.h
index ad50c7d5..11194b3e 100644
--- a/src/sensors/HallSensor.h
+++ b/src/sensors/HallSensor.h
@@ -90,7 +90,7 @@ class HallSensor: public Sensor{
     // function pointer for on sector change call back
     void (*onSectorChange)(int sector) = nullptr;
 
-    volatile long pulse_diff;
+    volatile unsigned long pulse_diff;
     
 };