[sam] Fixed initialization of ADC timings (improves analogRead speed by a factor x10)

Discussion:
http://www.djerickson.com/arduino/
http://forum.arduino.cc/index.php?topic=156849
http://forum.arduino.cc/index.php?topic=187693

Fixes #1418

Author: cmaglie

build/shared/revisions.txt

@@ -7,6 +7,10 @@ ARDUINO 1.5.5 BETA
 * sam: Fixed SPI initialization (when using extended API and multiple CS)
 * avr: Fixed behavior of EthernetClient::flush()
 
+[core]
+* sam: Fixed wrong initialization for ADC timings (analogRead speed Arduino DUE improved by a factor x10)
+       (http://www.djerickson.com/arduino/)
+
 ARDUINO 1.5.4 BETA 2013.09.10
 
 [ide]

hardware/arduino/sam/variants/arduino_due_x/variant.cpp

@@ -433,7 +433,7 @@ void init( void )
 
   // Initialize Analog Controller
   pmc_enable_periph_clk(ID_ADC);
-  adc_init(ADC, SystemCoreClock, ADC_FREQ_MAX, ADC_STARTUP_FAST);
+  adc_init(ADC, SystemCoreClock, ADC_FREQ_MAX, /*ADC_STARTUP_FAST*/ 3);
   adc_configure_timing(ADC, 0, ADC_SETTLING_TIME_3, 1);
   adc_configure_trigger(ADC, ADC_TRIG_SW, 0); // Disable hardware trigger.
   adc_disable_interrupt(ADC, 0xFFFFFFFF); // Disable all ADC interrupts.