m68knommu: init coldfire timer TRR with n - 1, not n

The coldfire timer must be initialised to n - 1 if we want it to count n cycles between each tick interrupt. This was already fixed, but has been lost with the conversion to GENERIC_TIMER. Signed-off-by: Philippe De Muyter <[email protected]> Acked-by: Greg Ungerer <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
josf · Jun 13, 2008 · 6c38d85 · 6c38d85
1 parent 67dddaa
commit 6c38d85
Showing 1 changed file with 7 additions and 1 deletion.
diff --git a/arch/m68knommu/platform/coldfire/timers.c b/arch/m68knommu/platform/coldfire/timers.c
@@ -111,7 +111,13 @@ void hw_timer_init(void)
 
 	__raw_writew(MCFTIMER_TMR_DISABLE, TA(MCFTIMER_TMR));
 	mcftmr_cycles_per_jiffy = FREQ / HZ;
-	__raw_writetrr(mcftmr_cycles_per_jiffy, TA(MCFTIMER_TRR));
+	/*
+	 *	The coldfire timer runs from 0 to TRR included, then 0
+	 *	again and so on.  It counts thus actually TRR + 1 steps
+	 *	for 1 tick, not TRR.  So if you want n cycles,
+	 *	initialize TRR with n - 1.
+	 */
+	__raw_writetrr(mcftmr_cycles_per_jiffy - 1, TA(MCFTIMER_TRR));
 	__raw_writew(MCFTIMER_TMR_ENORI | MCFTIMER_TMR_CLK16 |
 		MCFTIMER_TMR_RESTART | MCFTIMER_TMR_ENABLE, TA(MCFTIMER_TMR));