From d5553f1830dfb662294eee18f2efb0799bb08754 Mon Sep 17 00:00:00 2001
From: InsanityAutomation
 <38436470+InsanityAutomation@users.noreply.github.com>
Date: Sun, 15 Mar 2020 19:29:18 -0400
Subject: [PATCH] Configurable SLOWDOWN divisor (#17171)

---
 Marlin/Configuration_adv.h    | 6 +++++-
 Marlin/src/module/planner.cpp | 5 ++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/Marlin/Configuration_adv.h b/Marlin/Configuration_adv.h
index bd22c3c53ba8..a52fccf5435d 100644
--- a/Marlin/Configuration_adv.h
+++ b/Marlin/Configuration_adv.h
@@ -753,8 +753,12 @@
 // Minimum time that a segment needs to take if the buffer is emptied
 #define DEFAULT_MINSEGMENTTIME        50000   // (ms)
 
-// If defined the movements slow down when the look ahead buffer is only half full
+// Slow down the machine if the look ahead buffer is (by default) half full.
+// Increase the slowdown divisor for larger buffer sizes.
 #define SLOWDOWN
+#if ENABLED(SLOWDOWN)
+  #define SLOWDOWN_DIVISOR 2
+#endif
 
 // Frequency limit
 // See nophead's blog for more info
diff --git a/Marlin/src/module/planner.cpp b/Marlin/src/module/planner.cpp
index 74177490882f..3b2daf1812e9 100644
--- a/Marlin/src/module/planner.cpp
+++ b/Marlin/src/module/planner.cpp
@@ -2041,7 +2041,10 @@ bool Planner::_populate_block(block_t * const block, bool split_move,
   #endif
 
   #if ENABLED(SLOWDOWN)
-    if (WITHIN(moves_queued, 2, (BLOCK_BUFFER_SIZE) / 2 - 1)) {
+    #ifndef SLOWDOWN_DIVISOR
+      #define SLOWDOWN_DIVISOR 2
+    #endif
+    if (WITHIN(moves_queued, 2, (BLOCK_BUFFER_SIZE) / (SLOWDOWN_DIVISOR) - 1)) {
       if (segment_time_us < settings.min_segment_time_us) {
         // buffer is draining, add extra time.  The amount of time added increases if the buffer is still emptied more.
         const uint32_t nst = segment_time_us + LROUND(2 * (settings.min_segment_time_us - segment_time_us) / moves_queued);