From dc3db0476b20a66b60d47f6c4be676b928363957 Mon Sep 17 00:00:00 2001
From: Buzz <davidbuzz@gmail.com>
Date: Mon, 18 May 2020 16:57:29 +1000
Subject: [PATCH] AP_Landing: option to keep landing throttle at thr_min during
 flare and touchdown, not zero.

---
 libraries/AP_Landing/AP_Landing.cpp | 15 ++++++++++++++-
 libraries/AP_Landing/AP_Landing.h   |  8 ++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/libraries/AP_Landing/AP_Landing.cpp b/libraries/AP_Landing/AP_Landing.cpp
index 5dc940cc09..007f3086c5 100644
--- a/libraries/AP_Landing/AP_Landing.cpp
+++ b/libraries/AP_Landing/AP_Landing.cpp
@@ -142,7 +142,14 @@ const AP_Param::GroupInfo AP_Landing::var_info[] = {
     // @Group: DS_
     // @Path: AP_Landing_Deepstall.cpp
     AP_SUBGROUPINFO(deepstall, "DS_", 15, AP_Landing, AP_Landing_Deepstall),
-    
+
+    // @Param: _OPTIONS
+    // @DisplayName: Landing options bitmask
+    // @Description: Bitmask of options to use with landing.
+    // @Bitmask: 0: honor min throttle during landing flare
+    // @User: Advanced
+    AP_GROUPINFO("OPTIONS", 16, AP_Landing, _options, 0),
+
     AP_GROUPEND
 };
 
@@ -606,6 +613,12 @@ bool AP_Landing::is_throttle_suppressed(void) const
     }
 }
 
+//defaults to false, but _options bit zero enables it.
+bool AP_Landing::use_thr_min_during_flare(void) const
+{
+    return (OptionsMask::ON_LANDING_FLARE_USE_THR_MIN & _options) != 0;
+}
+
 /*
  * returns false when the vehicle might not be flying forward while landing
  */
diff --git a/libraries/AP_Landing/AP_Landing.h b/libraries/AP_Landing/AP_Landing.h
index 672f00fc53..82d447bbef 100644
--- a/libraries/AP_Landing/AP_Landing.h
+++ b/libraries/AP_Landing/AP_Landing.h
@@ -57,6 +57,11 @@ public:
 //      TODO: TYPE_HELICAL,
     };
 
+    // we support upto 32 boolean bits for users wanting to change landing behaviour.
+    enum OptionsMask {
+        ON_LANDING_FLARE_USE_THR_MIN                   = (1<<0),   // If set then set trottle to thr_min instead of zero on final flare
+    };
+
     void do_land(const AP_Mission::Mission_Command& cmd, const float relative_altitude);
     bool verify_abort_landing(const Location &prev_WP_loc, Location &next_WP_loc, const Location &current_loc,
             const int32_t auto_state_takeoff_altitude_rel_cm, bool &throttle_suppressed);
@@ -72,6 +77,7 @@ public:
     bool is_ground_steering_allowed(void) const;
     bool is_throttle_suppressed(void) const;
     bool is_flying_forward(void) const;
+    bool use_thr_min_during_flare(void) const; //defaults to false, but _options bit zero enables it.
     void handle_flight_stage_change(const bool _in_landing_stage);
     int32_t constrain_roll(const int32_t desired_roll_cd, const int32_t level_roll_limit_cd);
     bool get_target_altitude_location(Location &location);
@@ -115,6 +121,8 @@ private:
         bool in_progress:1;
     } flags;
 
+    AP_Int16 _options;    // user-configurable bitmask options, via a parameter, for landing
+
     // same as land_slope but sampled once before a rangefinder changes the slope. This should be the original mission planned slope
     float initial_slope;