How to change from Timer1 (16-bit) to Timer0 (8-bit) in AVR Arduino port and set timer tick to 1 ms.

atomthread-avr-use-timer0.diff

diff --git a/ports/avr/atomport.c b/ports/avr/atomport.c
index 9ae5555..4107a1d 100644
--- a/ports/avr/atomport.c
+++ b/ports/avr/atomport.c
@@ -277,21 +277,21 @@ void archThreadContextInit (ATOM_TCB *tcb_ptr, void *stack_top, void (*entry_poi
  */
 void avrInitSystemTickTimer ( void )
 {
-    /* Set timer 1 compare match value for configured system tick,
-     * with a prescaler of 256. We will get a compare match 1A
+    /* Set timer 0 compare match value for configured system tick,
+     * with a prescaler of 64. We will get a compare match 1A
      * interrupt on every system tick, in which we must call the
      * OS's system tick handler. */
-    OCR1A = (AVR_CPU_HZ / 256 / SYSTEM_TICKS_PER_SEC);
+    OCR0A = (AVR_CPU_HZ / 64 / SYSTEM_TICKS_PER_SEC);
 
     /* Enable compare match 1A interrupt */
 #ifdef TIMSK
-    TIMSK = _BV(OCIE1A);
+    TIMSK = _BV(OCIE0A);
 #else
-    TIMSK1 = _BV(OCIE1A);
+    TIMSK0 = _BV(OCIE0A);
 #endif
 
-    /* Set prescaler 256 */
-    TCCR1B = _BV(CS12) | _BV(WGM12);
+    /* Set prescaler 64 */
+    TCCR0B = _BV(CS01) |_BV(CS00) | _BV(WGM02);
 }
 
 
@@ -324,7 +324,7 @@ void avrInitSystemTickTimer ( void )
  *
  * @return None
  */
-ISR (TIMER1_COMPA_vect)
+ISR (TIMER0_COMPA_vect)
 {
     /* Call the interrupt entry routine */
     atomIntEnter();
diff --git a/ports/avr/atomport.h b/ports/avr/atomport.h
index 875bd15..12ff3ae 100644
--- a/ports/avr/atomport.h
+++ b/ports/avr/atomport.h
@@ -40,8 +40,8 @@
 /* Definition of NULL is available from stddef.h on this platform */
 #include <stddef.h>
 
-/* Required number of system ticks per second (normally 100 for 10ms tick) */
-#define SYSTEM_TICKS_PER_SEC            100
+/* Required number of system ticks per second (normally 1000 for 1ms tick) */
+#define SYSTEM_TICKS_PER_SEC            1000
 
 /* Size of each stack entry / stack alignment size (8 bits on AVR) */
 #define STACK_ALIGN_SIZE                sizeof(uint8_t)