DDA: Move axis calculations into loops, part 6a.

Clean up code to reduce duplication by consolidating code into
loops for per-axis actions.

Part 6a is putting stuff inside the step interrupt into a loop,
too. do_step() is put into the "tidiest" place. Binary size goes
down a remarkable 374 bytes, but stepping performance suffers by
almost 30%.

Traumflug's performance measurements:

    SIZES             ATmega...  '168    '328(P)    '644(P)    '1280
    FLASH : 19908 bytes          139%       65%        32%       16%
    RAM   :  2302 bytes          225%      113%        57%       29%
    EEPROM:    32 bytes            4%        2%         2%        1%

short-moves.gcode
Statistics (assuming a 20 MHz clock):
LED on occurences: 888.
Sum of all LED on time: 354537 clock cycles.
LED on time minimum: 390 clock cycles.
LED on time maximum: 806 clock cycles.
LED on time average: 399.253 clock cycles.

smooth-curves.gcode
Statistics (assuming a 20 MHz clock):
LED on occurences: 9124.
Sum of all LED on time: 4268896 clock cycles.
LED on time minimum: 395 clock cycles.
LED on time maximum: 807 clock cycles.
LED on time average: 467.875 clock cycles.

triangle-odd.gcode
Statistics (assuming a 20 MHz clock):
LED on occurences: 1636.
Sum of all LED on time: 706846 clock cycles.
LED on time minimum: 390 clock cycles.
LED on time maximum: 807 clock cycles.
LED on time average: 432.057 clock cycles.

dda.c

@@ -482,78 +482,26 @@ void dda_start(DDA *dda) {
 	Finally we de-assert any asserted step pins.
 */
 void dda_step(DDA *dda) {
+  enum axis_e i;
 
-#if ! defined ACCELERATION_TEMPORAL
-  if (move_state.steps[X]) {
-    move_state.counter[X] -= dda->delta[X];
-    if (move_state.counter[X] < 0) {
-			x_step();
-      move_state.steps[X]--;
-      move_state.counter[X] += dda->total_steps;
-		}
-	}
-#else	// ACCELERATION_TEMPORAL
-	if (dda->axis_to_step == X) {
-		x_step();
-    move_state.steps[X]--;
-    move_state.time[X] += dda->step_interval[X];
-    move_state.all_time = move_state.time[X];
-	}
-#endif
-
-#if ! defined ACCELERATION_TEMPORAL
-  if (move_state.steps[Y]) {
-    move_state.counter[Y] -= dda->delta[Y];
-    if (move_state.counter[Y] < 0) {
-			y_step();
-      move_state.steps[Y]--;
-      move_state.counter[Y] += dda->total_steps;
-		}
-	}
-#else	// ACCELERATION_TEMPORAL
-	if (dda->axis_to_step == Y) {
-		y_step();
-    move_state.steps[Y]--;
-    move_state.time[Y] += dda->step_interval[Y];
-    move_state.all_time = move_state.time[Y];
-	}
-#endif
-
-#if ! defined ACCELERATION_TEMPORAL
-  if (move_state.steps[Z]) {
-    move_state.counter[Z] -= dda->delta[Z];
-    if (move_state.counter[Z] < 0) {
-			z_step();
-      move_state.steps[Z]--;
-      move_state.counter[Z] += dda->total_steps;
-		}
-	}
-#else	// ACCELERATION_TEMPORAL
-	if (dda->axis_to_step == Z) {
-		z_step();
-    move_state.steps[Z]--;
-    move_state.time[Z] += dda->step_interval[Z];
-    move_state.all_time = move_state.time[Z];
-	}
-#endif
-
-#if ! defined ACCELERATION_TEMPORAL
-  if (move_state.steps[E]) {
-    move_state.counter[E] -= dda->delta[E];
-    if (move_state.counter[E] < 0) {
-			e_step();
-      move_state.steps[E]--;
-      move_state.counter[E] += dda->total_steps;
-		}
-	}
-#else	// ACCELERATION_TEMPORAL
-	if (dda->axis_to_step == E) {
-		e_step();
-    move_state.steps[E]--;
-    move_state.time[E] += dda->step_interval[E];
-    move_state.all_time = move_state.time[E];
-	}
-#endif
+  #if ! defined ACCELERATION_TEMPORAL
+    for (i = X; i < AXIS_COUNT; i++) {
+      if (move_state.steps[i]) {
+        move_state.counter[i] -= dda->delta[i];
+        if (move_state.counter[i] < 0) {
+          do_step(i);
+          move_state.steps[i]--;
+          move_state.counter[i] += dda->total_steps;
+        }
+      }
+    }
+  #else // ACCELERATION_TEMPORAL
+    i = dda->axis_to_step;
+    do_step(i);
+    move_state.steps[i]--;
+    move_state.time[i] += dda->step_interval[i];
+    move_state.all_time = move_state.time[i];
+  #endif
 
 	#if STEP_INTERRUPT_INTERRUPTIBLE && ! defined ACCELERATION_RAMPING
 		// Since we have sent steps to all the motors that will be stepping

pinio.c

@@ -42,3 +42,16 @@ void power_off() {
 
 	ps_is_on = 0;
 }
+
+// step the 'n' axis
+void do_step(enum axis_e n) {
+  if (n == X)
+    x_step();
+  else if (n == Y)
+    y_step();
+  else if (n == Z)
+    z_step();
+  else if (n == E)
+    e_step();
+}
+

pinio.h

@@ -6,6 +6,7 @@
 #define	_PINIO_H
 
 #include	"config_wrapper.h"
+#include "dda.h"
 
 #ifdef SIMULATOR
   #include "simulator.h"
@@ -33,6 +34,8 @@ inline void power_init(void) {
 void power_on(void);
 void power_off(void);
 
+void do_step(enum axis_e n);
+
 /*
 X Stepper
 */