From d7ff10163c270a926c26f54d4fb7e43725cac4b6 Mon Sep 17 00:00:00 2001
From: Iampete1 <iampete@hotmail.co.uk>
Date: Wed, 9 Feb 2022 00:32:46 +0000
Subject: [PATCH] AP_Button: trigger low on invalid PWM input

---
 libraries/AP_Button/AP_Button.cpp | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/libraries/AP_Button/AP_Button.cpp b/libraries/AP_Button/AP_Button.cpp
index 1349341abb..2b993f40b5 100644
--- a/libraries/AP_Button/AP_Button.cpp
+++ b/libraries/AP_Button/AP_Button.cpp
@@ -74,27 +74,27 @@ const AP_Param::GroupInfo AP_Button::var_info[] = {
 
     // @Param: OPTIONS1
     // @DisplayName: Button Pin 1 Options
-    // @Description: Options for Pin 1. PWM input detects PWM above or below 1800/1200us instead of logic level. Invert changes HIGH state to be logic low voltage on pin, or below 1200us, if PWM input.
+    // @Description: Options for Pin 1. PWM input detects PWM above or below 1800/1200us instead of logic level. If PWM is not detected or is less than 800us or above 2200us the button will interpreted as low. Invert changes HIGH state to be logic low voltage on pin, or below 1200us, if PWM input.
     // @User: Standard
     // @Bitmask: 0:PWM Input,1:InvertInput
     AP_GROUPINFO("OPTIONS1",  6, AP_Button, options[0], 0),
 
     // @Param: OPTIONS2
     // @DisplayName: Button Pin 2 Options
-    // @Description: Options for Pin 2. PWM input detects PWM above or below 1800/1200us instead of logic level. Invert changes HIGH state to be logic low voltage on pin, or below 1200us, if PWM input.
+    // @Description: Options for Pin 2. PWM input detects PWM above or below 1800/1200us instead of logic level. If PWM is not detected or is less than 800us or above 2200us the button will interpreted as low. Invert changes HIGH state to be logic low voltage on pin, or below 1200us, if PWM input.
     // @User: Standard
     // @Bitmask: 0:PWM Input,1:InvertInput
     AP_GROUPINFO("OPTIONS2",  7, AP_Button, options[1], 0),
 
     // @Param: OPTIONS3
     // @DisplayName: Button Pin 3 Options
-    // @Description: Options for Pin 3. PWM input detects PWM above or below 1800/1200us instead of logic level. Invert changes HIGH state to be logic low voltage on pin, or below 1200us, if PWM input.
+    // @Description: Options for Pin 3. PWM input detects PWM above or below 1800/1200us instead of logic level. If PWM is not detected or is less than 800us or above 2200us the button will interpreted as low. Invert changes HIGH state to be logic low voltage on pin, or below 1200us, if PWM input.
     // @Bitmask: 0:PWM Input,1:InvertInput
     AP_GROUPINFO("OPTIONS3",  8, AP_Button, options[2], 0),
 
     // @Param: OPTIONS4
     // @DisplayName: Button Pin 4 Options
-    // @Description: Options for Pin 4. PWM input detects PWM above or below 1800/1200us instead of logic level. Invert changes HIGH state to be logic low voltage on pin, or below 1200us, if PWM input.
+    // @Description: Options for Pin 4. PWM input detects PWM above or below 1800/1200us instead of logic level. If PWM is not detected or is less than 800us or above 2200us the button will interpreted as low. Invert changes HIGH state to be logic low voltage on pin, or below 1200us, if PWM input.
     // @User: Standard
     // @Bitmask: 0:PWM Input,1:InvertInput
     AP_GROUPINFO("OPTIONS4",  9, AP_Button, options[3], 0),
@@ -183,6 +183,13 @@ void AP_Button::update(void)
             continue;
         }
         const uint16_t pwm_us = pwm_pin_source[i].get_pwm_us();
+        if (pwm_us < RC_Channel::RC_MIN_LIMIT_PWM || pwm_us > RC_Channel::RC_MAX_LIMIT_PWM) {
+            // invalid pulse width, trigger low
+            if (pwm_state & mask) {
+                new_pwm_state &= ~mask;
+            }
+            continue;
+        }
         // these values are the same as used in RC_Channel:
         if (pwm_state & mask) {
             // currently asserted; check to see if we should de-assert