From d3fa070d10331727b9094b4976a94a8143dcba30 Mon Sep 17 00:00:00 2001
From: "David A. Mellis" <d.mellis@arduino.cc>
Date: Fri, 21 Oct 2011 11:54:11 -0400
Subject: [PATCH] Lowering timer 1 prescale factor (to 8 from 64) for F_CPU
 less than 8 MHz.

Otherwise, you can see flicker on an LED.
---
 cores/arduino/wiring.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/cores/arduino/wiring.c b/cores/arduino/wiring.c
index 1b3fd44..bc01949 100755
--- a/cores/arduino/wiring.c
+++ b/cores/arduino/wiring.c
@@ -221,10 +221,14 @@ void init()
 
 	// set timer 1 prescale factor to 64
 	sbi(TCCR1B, CS11);
+#if F_CPU >= 8000000L
 	sbi(TCCR1B, CS10);
+#endif
 #elif defined(TCCR1) && defined(CS11) && defined(CS10)
 	sbi(TCCR1, CS11);
+#if F_CPU >= 8000000L
 	sbi(TCCR1, CS10);
+#endif
 #endif
 	// put timer 1 in 8-bit phase correct pwm mode
 #if defined(TCCR1A) && defined(WGM10)