Remove volatile from next_step_time as it can be easily managed using

memory barriers since it is only touched inside a single interrupt
handler or while interrupts are disabled in setTimer().

This saves about 90 bytes since it no longer needs to be reloaded multiple
times.

timer.c

@@ -19,13 +19,15 @@
 #include	"dda_queue.h"
 #endif
 
+#include	"memory_barrier.h"
+
 /// how often we overflow and update our clock; with F_CPU=16MHz, max is < 4.096ms (TICK_TIME = 65535)
 #define		TICK_TIME			2 MS
 /// convert back to ms from cpu ticks so our system clock runs properly if you change TICK_TIME
 #define		TICK_TIME_MS	(TICK_TIME / (F_CPU / 1000))
 
 /// time until next step, as output compare register is too small for long step times
-volatile uint32_t	next_step_time;
+uint32_t	next_step_time;
 
 /// every time our clock fires, we increment this so we know when 10ms has elapsed
 uint8_t						clock_counter_10ms = 0;
@@ -125,9 +127,11 @@ void setTimer(uint32_t delay)
 	// save interrupt flag
 	uint8_t sreg = SREG;
 	uint16_t step_start = 0;
+	
 	// disable interrupts
 	cli();
-
+	CLI_SEI_BUG_MEMORY_BARRIER();
+	
 	// re-enable clock interrupt in case we're recovering from emergency stop
 	TIMSK1 |= MASK(OCIE1B);
 
@@ -173,6 +177,7 @@ void setTimer(uint32_t delay)
 	}
 
 	// restore interrupt flag
+	MEMORY_BARRIER();
 	SREG = sreg;
 }