From 20686eb52c218b74cd0f2337bddf330acc4b74ec Mon Sep 17 00:00:00 2001
From: Markus Hitter <mah@jump-ing.de>
Date: Sat, 30 Nov 2013 23:22:13 +0100
Subject: [PATCH] dda.c: remove the hack for too high rampup steps for
 lookahead.

Keeping the hack causes the previous move to decelerate, which isn't
intended when movements are joined with lookahead.

Removing only the hack breaks endstop handling on those axes which
set a huuuge number of acceleration steps for the lack of a proper
calculation algorithm. We have this algorithm now, so we can stop
using this kludge.

Solves part 1 of issue #68.
---
 dda.c | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/dda.c b/dda.c
index 202a5ac..be226e1 100644
--- a/dda.c
+++ b/dda.c
@@ -368,13 +368,6 @@ void dda_create(DDA *dda, TARGET *target) {
       }
       dda->rampup_steps = ACCELERATE_RAMP_LEN(muldiv(fast_um, dda->endpoint.F, distance));
 
-      // Quick hack: we do not do Z move joins as jerk on the Z axis is undesirable;
-      // as the ramp length is calculated for XY, its incorrect for Z: apply the original
-      // 'fix' to simply specify a large enough ramp for any speed.
-      if (x_delta_um == 0 && y_delta_um == 0) {
-        dda->rampup_steps = 1000000; // replace mis-calculation by a safe value
-      }
-
       if (dda->rampup_steps > dda->total_steps / 2)
         dda->rampup_steps = dda->total_steps / 2;
       dda->rampdown_steps = dda->total_steps - dda->rampup_steps;
@@ -867,6 +860,9 @@ void dda_clock() {
         // approximation here: c0 * (1 / (2 * sqrt(n))).
         move_c = ((C0 >> 8) * int_inv_sqrt(dda->n)) >> 5;
 
+      // TODO: most likely this whole check is obsolete. It was left as a
+      //       safety margin, only. Rampup steps calculation should be accurate
+      //       now and give the requested target speed within a few percent.
       if (move_c < dda->c_min) {
         // We hit max speed not always exactly.
         move_c = dda->c_min;
@@ -874,14 +870,8 @@ void dda_clock() {
         // This is a hack which deals with movements with an unknown number of
         // acceleration steps. dda_create() sets a very high number, then,
         // but we don't want to re-calculate all the time.
-        // This hack doesn't work with (and isn't neccessary for) movements
-        // accelerated by look-ahead.
-        #ifdef LOOKAHEAD
-          if (dda->crossF == 0) {  // For example, endstop searches.
-            dda->rampup_steps = move_step_no;
-            dda->rampdown_steps = dda->total_steps - dda->rampup_steps;
-          }
-        #else  // Without LOOKAHEAD, there's no dda->crossF.
+        // This hack doesn't work with lookahead.
+        #ifndef LOOKAHEAD
           dda->rampup_steps = move_step_no;
           dda->rampdown_steps = dda->total_steps - dda->rampup_steps;
         #endif