linux-kernel - [PATCH] m68knommu: init coldfire timer TRR with n

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Message-ID: <20080610210642.GA23486@frolo.macqel>
Date:	Tue, 10 Jun 2008 23:06:42 +0200
From:	Philippe De Muyter <phdm@...qel.be>
To:	linux-kernel@...r.kernel.org, uclinux-dev@...inux.org
Subject: [PATCH] m68knommu: init coldfire timer TRR with n - 1, not n

Hello everybody,

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 <phdm@...qel.be>

diff -r 184e1bb486cf arch/m68knommu/platform/coldfire/timers.c
--- a/arch/m68knommu/platform/coldfire/timers.c	Mon Jun  9 19:30:13 2008 -0700
+++ b/arch/m68knommu/platform/coldfire/timers.c	Tue Jun 10 13:25:22 2008 +0200
@@ -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));
 
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