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Use (CLK_PER / 2) instead of CLKTCA for millis / micros clock #72

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Use (CLK_PER / 2) instead of CLKTCA for millis / micros clock #72

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41 changes: 24 additions & 17 deletions cores/arduino/wiring.c
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,7 @@ uint16_t fract_inc;

// whole number of microseconds per timer tick

volatile uint8_t timer_counter = 0;
volatile uint32_t timer_overflow_count = 0;
volatile uint32_t timer_millis = 0;
static uint16_t timer_fract = 0;
Expand Down Expand Up @@ -85,22 +86,28 @@ ISR(TCB3_INT_vect)
ISR(TCB0_INT_vect)
#endif
{
// copy these to local variables so they can be stored in registers
// (volatile variables must be read from memory on every access)
uint32_t m = timer_millis;
uint16_t f = timer_fract;

m += millis_inc;
f += fract_inc;
if (f >= FRACT_MAX) {

f -= FRACT_MAX;
m += 1;
uint8_t c = timer_counter;
if (c % 32 == 0) {
// copy these to local variables so they can be stored in registers
// (volatile variables must be read from memory on every access)
uint32_t m = timer_millis;
uint16_t f = timer_fract;

m += millis_inc;
f += fract_inc;
if (f >= FRACT_MAX) {

f -= FRACT_MAX;
m += 1;
}

timer_fract = f;
timer_millis = m;
timer_overflow_count++;
}

timer_fract = f;
timer_millis = m;
timer_overflow_count++;

c++;
timer_counter = c;

/* Clear flag */
_timer->INTFLAGS = TCB_CAPT_bm;
Expand Down Expand Up @@ -396,8 +403,8 @@ void init()
/* Enable timer interrupt */
_timer->INTCTRL |= TCB_CAPT_bm;

/* Clock selection -> same as TCA (F_CPU/64 -- 250kHz) */
_timer->CTRLA = TCB_CLKSEL_CLKTCA_gc;
/* Clock selection -> F_CPU / 2, then we only run the ISR every 32 interrupts. (F_CPU/2/32 = 250kHz) */
_timer->CTRLA = TCB_CLKSEL_CLKDIV2_gc;

/* Enable & start */
_timer->CTRLA |= TCB_ENABLE_bm; /* Keep this last before enabling interrupts to ensure tracking as accurate as possible */
Expand Down