fix zjerk being the same for delta as xy jerk

add more delta defaults
on delta make second home even slower

Marlin/Configuration.h

 
 // The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
+#ifdef DELTA
+#define DEFAULT_ZJERK                 20.0    // (mm/sec) Must be same as XY for delta
+#else
 #define DEFAULT_ZJERK                 0.4     // (mm/sec)
+#endif // DELTA
 #define DEFAULT_EJERK                 5.0    // (mm/sec)
 
 //===========================================================================

Marlin/Configuration_adv.h

 #define DEFAULT_MINSEGMENTTIME        20000
 
 // If defined the movements slow down when the look ahead buffer is only half full
+// (don't use SLOWDOWN with DELTA because DELTA generates hundreds of segments per second)
+#ifndef DELTA
 #define SLOWDOWN
+#endif
 
 // Frequency limit
 // See nophead's blog for more info

Marlin/Marlin_main.cpp

     st_synchronize();
 
     destination[axis] = 2*home_retract_mm(axis) * home_dir(axis);
+#ifdef DELTA
+    feedrate = homing_feedrate[axis]/10;
+#else
     feedrate = homing_feedrate[axis]/2 ;
+#endif
     plan_buffer_line(destination[X_AXIS], destination[Y_AXIS], destination[Z_AXIS], destination[E_AXIS], feedrate/60, active_extruder);
     st_synchronize();