From ae70c6cbe3111df9a685e052320a3eb99cf97932 Mon Sep 17 00:00:00 2001
From: Dietz0r <102995203+Dietz0r@users.noreply.github.com>
Date: Wed, 8 Jan 2025 09:06:00 +0100
Subject: [PATCH] improved deceleration ramp behaviour - cleaned up code a bit
 Thanks to @Engigneer, @fpq473 for helping figuring this out!

---
 stepper.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/stepper.c b/stepper.c
index bddb345..ffe04f4 100644
--- a/stepper.c
+++ b/stepper.c
@@ -877,7 +877,7 @@ void st_prep_buffer (void)
         float minimum_mm = mm_remaining - prep.req_mm_increment; // Guarantee at least one step.
 #if ENABLE_ACCELERATION_PROFILES
         float time_to_jerk;     // time needed for jerk ramp
-        float mm_to_rampend;    // mm needed to complete one jerk ramp mm == V(0)*T + 1/2 A0*T^2 + 1/6 J*T^3
+        float jerk_rampdown;    // calculated startpoint of jerk rampdown
 #endif
 
         if (minimum_mm < 0.0f)
@@ -905,10 +905,10 @@ void st_prep_buffer (void)
                     // NOTE: Acceleration ramp only computes during first do-while loop.
 #if ENABLE_JERK_ACCELERATION
                     time_to_jerk = last_segment_accel / pl_block->jerk;
-                    mm_to_rampend = (prep.current_speed * time_to_jerk) + (0.5f * last_segment_accel * time_to_jerk * time_to_jerk) + (pl_block->jerk * time_to_jerk * time_to_jerk * time_to_jerk) / 6.0f;  //Distance to 0 acceleration at speed
-                    if ((mm_remaining - prep.accelerate_until) > mm_to_rampend) {
+                    jerk_rampdown =time_to_jerk * (prep.current_speed + (0.5f * last_segment_accel * time_to_jerk) + (pl_block->jerk * time_to_jerk * time_to_jerk) / 6.0f);  //Distance to 0 acceleration at speed (mm == V(0)*T + 1/2 A0*T^2 + 1/6 J*T^3)
+                    if ((mm_remaining - prep.accelerate_until) > jerk_rampdown) {
                         //+1.0f to avoid divide by 0 speed, minor effect on jerk ramp
-                        // Check if we are on ramp up or ramp down. Ramp down if time to end of acceleration is less than time needed to reach 0 acceleration.
+                        // Check if we are on ramp up or ramp down. Ramp down if distance to end of acceleration is less than distance needed to reach 0 acceleration.
                         // Then limit acceleration change by jerk up to max acceleration and update for next segment.
                         // Minimum acceleration jerk per time_var to ensure acceleration completes. Acceleration change at end of ramp is in acceptable jerk range.
                         last_segment_accel = min(last_segment_accel + pl_block->jerk * time_var, pl_block->max_acceleration); 
@@ -951,9 +951,9 @@ void st_prep_buffer (void)
                     // NOTE: mm_var used as a misc worker variable to prevent errors when near zero speed.
 #if ENABLE_JERK_ACCELERATION   
                     time_to_jerk = last_segment_accel / pl_block->jerk;
-                    mm_to_rampend = (0.5f * last_segment_accel * time_to_jerk * time_to_jerk) + (pl_block->jerk * time_to_jerk * time_to_jerk * time_to_jerk) / 6.0f; // Distance to 0 acceleration
-                    if (mm_remaining > mm_to_rampend) {
-                        // Check if we are on ramp up or ramp down. Ramp down if travel distance to end of deceleration is less than distance needed to reach 0 acceleration.
+                    jerk_rampdown = prep.exit_speed + time_to_jerk * (last_segment_accel - (0.5f * pl_block->jerk * time_to_jerk)); // Speedpoint to start ramping down deceleration. (V = a * t - 1/2 j * t^2)
+                    if (prep.current_speed > jerk_rampdown) {
+                        // Check if we are on ramp up or ramp down. Ramp down if speed is less than speed needed for reaching 0 acceleration.
                         // Then limit acceleration change by jerk up to max acceleration and update for next segment.
                         // Minimum acceleration of jerk per time_var to ensure deceleration completes. Acceleration change at end of ramp is in acceptable jerk range.
                         last_segment_accel = min(last_segment_accel + pl_block->jerk * time_var, pl_block->max_acceleration);