X-Git-Url: https://codewiz.org/gitweb?a=blobdiff_plain;f=bertos%2Fdrv%2Ftimer.c;h=d75f15abcf85324e525444bd3ad060404f196c56;hb=4bef9e1478a89338bece87b04c3872e76b64068e;hp=d380e5f1d458de07e0342281cbc84a934c80fdb2;hpb=f35b6066ecdeffcc8998dd566b5246bdcf43c548;p=bertos.git

diff --git a/bertos/drv/timer.c b/bertos/drv/timer.c
index d380e5f1..d75f15ab 100644
--- a/bertos/drv/timer.c
+++ b/bertos/drv/timer.c
@@ -286,15 +286,30 @@ void timer_busyWait(hptime_t delay)
 	hptime_t now, prev = timer_hw_hpread();
 	hptime_t delta;
 
-	for(;;)
+	for (;;)
 	{
 		now = timer_hw_hpread();
 		/*
-		 * We rely on hptime_t being unsigned here to
-		 * reduce the modulo to an AND in the common
-		 * case of TIMER_HW_CNT.
+		 * The timer counter may wrap here and "prev" can become
+		 * greater than "now". So, be sure to always evaluate a
+		 * coherent timer difference:
+		 *
+		 * 0     prev            now   TIMER_HW_CNT
+		 * |_____|_______________|_____|
+		 *        ^^^^^^^^^^^^^^^
+		 * delta = now - prev
+		 *
+		 * 0     now             prev  TIMER_HW_CNT
+		 * |_____|_______________|_____|
+		 *  ^^^^^                 ^^^^^
+		 * delta = (TIMER_HW_CNT - prev) + now
+		 *
+		 * NOTE: TIMER_HW_CNT can be any value, not necessarily a power
+		 * of 2. For this reason the "%" operator is not suitable for
+		 * the generic case.
 		 */
-		delta = (now - prev) % TIMER_HW_CNT;
+		delta = (now < prev) ? ((hptime_t)TIMER_HW_CNT - prev + now) :
+						(now - prev);
 		if (delta >= delay)
 			break;
 		delay -= delta;
@@ -357,7 +372,7 @@ DEFINE_TIMER_ISR
 
 	/* Perform hw IRQ handling */
 	timer_hw_irq();
-	
+
 	TIMER_STROBE_OFF;
 }