Je besser die Hardware, desto kompakter der Code.
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#include <avr/io.h>
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int main(void)
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{
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const uint32_t coefficient = 2577; // coefficient (@ 3.33 MHz main clock)
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uint16_t frequency = 500; // frequency (Hz)
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uint32_t tcfcmp = coefficient * frequency >> 8; // compare value for TCF0.CMP
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TCF0.CTRLB = TCF_WGMODE_NCOFDC_gc; // NCO fixed duty-cycle
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while(TCF0.STATUS){}; // wait if busy
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TCF0.CMP = tcfcmp; // write compare value
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TCF0.CTRLC = TCF_WO0EN_bm; // enable TCF WO0 (PA0)
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TCF0.CTRLA = TCF_ENABLE_bm; // enable TCF
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TCB0.CCMP = 0x8234; // timeout value (20ms)
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TCB0.CTRLA = TCB_CLKSEL_DIV2_gc | TCB_ENABLE_bm; // 1.666 MHz, enable TCB0
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while(1)
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{
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if(TCB0.INTFLAGS)
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{
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TCB0.INTFLAGS = TCB_CAPT_bm; // clear TCB0 interrupt flag
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frequency += 1;
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if(frequency > 1000)
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{
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frequency = 500;
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}
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tcfcmp = coefficient * frequency >> 8; // calculate
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while(TCF0.STATUS & TCF_CMP0BUSY_bm){}; // wait if busy
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TCF0.CMP = tcfcmp; // update
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}
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}
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}
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AVR16EB14 Data Sheet:
"This linear advantage over divide-by-n timers comes at the cost of the output jitter. However, the jitter that occurs periodically is always plus or minus one clock period, depending on the division remainder."
