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#include <xc.h>
#include <stdint.h>
#include "system.h"
#include "types.h"
// (pulse/min) = 60 * (Fosc/4) / ((pre)*(post)*(PR2+1)*(period))
// = 60 * (48e6/4) / (64*16*10*(period))
// = 70313 / (period)
#define SPEED_FACTOR 70313ul
#define MIN_SPEED_PULSE_PER_MIN 2u // (pulse/min) >= SPEED_FACTOR / period_max)
#define EDGE_PER_PULSE 2u // rising and falling edge
static volatile U16 tmr2Period = 0u;
void
main(void) {
sysInit();
U16 pulsePerMin = 550u;
tmr2Period = ((U32)SPEED_FACTOR / pulsePerMin) & 0xFFFF;
T2CON = 0x7F; // postscaler=1:16, enable=1, prescaler=1:64
PR2 = 10u-1u; // period = PR2+1
INTCON = 0x00;
PIE1bits.TMR2IE = 1;
INTCONbits.PEIE = 1;
INTCONbits.GIE = 1;
for (;;) {
}
}
void __interrupt()
isr(void) {
static U16 tmr2Ctr = 0u;
if (TMR2IF) { // speedometer
if (++tmr2Ctr >= (tmr2Period/EDGE_PER_PULSE)) {
tmr2Ctr = 0u;
SPEED_PIN ^= 1; // toggle speedometer output
}
TMR2IF = 0;
}
}
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