Option to use 32768Hz watch crystal for timing. Code suggested by Georg von Zengen.

cpu/avr/dev/clock-avr.h

@@ -37,7 +37,44 @@
   TIMSK = _BV (OCIE0);
 
 #elif defined (__AVR_ATmega1284P__) || (__AVR_AT90USB1287__) || (__AVR_ATmega1281__)
-
+/*
+  The Raven has a 32768Hz watch crystal that can be used to clock the timer
+  while the 1284p is sleeping. The Jackdaw has pads for a crystal. The crystal
+  can be used to clock the 8 bit timer2.
+*/
+#if AVR_CONF_USE32KCRYSTAL
+#define OCRSetup() \
+  /* Clock from crystal on TOSC0-1 */ \
+  ASSR = _BV(AS2);		      \
+\
+  /* Set counter to zero */   \
+  TCNT2 = 0;				  \
+\
+  /*						  \
+   * Set comparison register: \
+   * Crystal freq. is 32768,\
+   * pre-scale factor is 8, we want 125 ticks / sec: \
+   * 32768 = 8 * 124.1 * 33, less 1 for CTC mode\
+   */ \
+  OCR2A = 32; \
+\
+  /* 								\
+   * Set timer control register: 	\
+   *  - prescale: 8 (CS21) \
+   *  - counter reset via comparison register (WGM21) \
+   */ 								\
+  TCCR2A = _BV(WGM21); \
+  TCCR2B = _BV(CS21);  \
+\
+  /* Clear interrupt flag register */ \
+  TIFR2 = TIFR2; \
+\
+  /* \
+   * Raise interrupt when value in OCR2 is reached. Note that the \
+   * counter value in TCNT2 is cleared automatically. \
+   */ \
+  TIMSK2 = _BV (OCIE2A);
+#else
 #define OCRSetup() \
   /* Select internal clock */ \
   ASSR = 0x00; 				  \
@@ -48,10 +85,10 @@
   /*						  \
    * Set comparison register: \
    * Crystal freq. is 8000000,\
-   * pre-scale factor is 1024, i.e. we have 125 "ticks" / sec: \
+   * pre-scale factor is 1024, we want 125 ticks / sec: \
-   * 8000000 = 1024 * 125 * 62.5 \
+   * 8000000 = 1024 * 126.01 * 62, less 1 for CTC mode \
    */ \
-  OCR0A = 62; \
+  OCR0A = 61; \
 \
   /* 								\
    * Set timer control register: 	\
@@ -69,6 +106,7 @@
    * counter value in TCNT0 is cleared automatically. \
    */ \
   TIMSK0 = _BV (OCIE0A);
+#endif /* AVR_CONF_USE32KCRYSTAL */
 
 #define AVR_OUTPUT_COMPARE_INT TIMER0_COMPA_vect
 

cpu/avr/dev/clock.c

@@ -6,19 +6,32 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 
-/* RADIOSTATS should be also be defined in the radio driver and webserver */
+static volatile clock_time_t count;
+static volatile uint8_t scount;
+volatile unsigned long seconds;
+
+/* Set RADIOSTATS to monitor radio on time (must also be set in the radio driver) */
 #if RF230BB && WEBSERVER
 #define RADIOSTATS 1
 #endif
 #if RADIOSTATS
-static volatile clock_time_t count, scount, rcount;
+static volatile uint8_t rcount;
-volatile unsigned long seconds,radioontime;
+volatile unsigned long radioontime;
 extern uint8_t RF230_receive_on;
-#else
-static volatile clock_time_t count, scount;
-volatile unsigned long seconds;
 #endif
 
+/*
+  CLOCK_SECOND is the number of ticks per second.
+  It is defined through CONF_CLOCK_SECOND in the contiki-conf.h for each platform.
+  The usual AVR default is ~125 ticks per second, counting a prescaler the CPU clock
+  using the 8 bit timer0.
+  
+  As clock_time_t is an unsigned 16 bit data type, intervals up to 524 seconds
+  can be measured with 8 millisecond precision. 
+  For longer intervals a 32 bit global is incremented every second. 
+ 
+  clock-avr.h contains the specific setup code for each mcu.
+*/
 /*---------------------------------------------------------------------------*/
 //SIGNAL(SIG_OUTPUT_COMPARE0)
 ISR(AVR_OUTPUT_COMPARE_INT)
@@ -41,49 +54,13 @@ ISR(AVR_OUTPUT_COMPARE_INT)
   }
 }
 
-/* External clock source does not work ? */
-#if 0
-void
-clock_init(void)
-{
-  cli ();
-  TIMSK &= ((unsigned char)~(1 << (TOIE0)));
-  TIMSK &= ((unsigned char)~(1 << (OCIE0)));
-  /* Disable TC0 interrupt */
-
-  /** 
-   *  set Timer/Counter0 to be asynchronous 
-   *  from the CPU clock with a second external 
-   *  clock(32,768kHz)driving it
-   */
-  ASSR |= (1 << (AS0));
-  TCCR0 = _BV (CS02) | _BV (CS01) | _BV (WGM1);
-
-  TCNT0 = 0;
-  OCR0 = 128;
-  
-  TIMSK |= (1 << (OCIE0));
-  TIMSK |= (1 << (TOIE0));
-  sei ();
-}
-#endif
-
 /*---------------------------------------------------------------------------*/
 void
 clock_init(void)
 {
   cli ();
-
-
   OCRSetup();
-
+//scount = count = 0;
-  /*
-   * Counts the number of ticks. Since clock_time_t is an unsigned
-   * 16 bit data type, time intervals of up to 524 seconds can be
-   * measured.
-   */
-  scount = count = 0;
-
   sei ();
 }