void calculate_power(volatile struct state_struct *pstate)
{
int32_t rest, power = 0;
uint8_t pulse_count;
cli();
rest = pstate->nano_end - pstate->nano_start;
pulse_count = pstate->pulse_count_final;
sei();
// Since the AVR has no dedicated floating-point hardware, we need
// to resort to fixed-point calculations for converting nWh/s to W.
// 1W = 10^6/3.6 nWh/s
// power[watt] = 3.6/10^6 * rest[nWh/s]
// power[watt] = 3.6/10^6 * 65536 * (rest[nWh/s] / 65536)
// power[watt] = 3.6/10^6 * 65536 * 262144 / 262144 * (rest[nWh/s] / 65536)
// power[watt] = 61847.53 / 262144 * (rest[nWh/s] / 65536)
// We have to correct for only using 666 samples iso 2000/3, so:
// power[watt] = 61847.53 * 1/666 * 2000/3 / 262144 * (rest[nWh/s] / 65536)
// power[watt] = 61909.44 / 262144 * (rest[nWh/s] / 65536)
// We round the constant down to 61909 to prevent 'underflow' in the
// consecutive else statement.
// The error introduced in the fixed-point rounding equals 7.1*10^-6.
MacU16X16to32(power, (uint16_t)(labs(rest)/65536), 61909);
power /= 262144;
if (rest >= 0) {
power += pulse_count*3600;
}
else {
power = pulse_count*3600 - power;
}
pstate->power = power;
}
void send(uint8_t msg_type, const struct sensor *measurement, const struct state *aux)
{
uint8_t i;
uint32_t value = 0;
uint32_t ms = 0;
int32_t rest;
uint8_t pulse_count;
char message[60];
switch (msg_type) {
case PULSE:
// blink the green LED
PORTB |= (1<<PB7);//DONE
_delay_ms(20);
PORTB &= ~(1<<PB7);//DONE
cli();
value = measurement->value;
ms = aux->time;
sei();
strcpy(message, "pls ");
break;
case POWER:
cli();
rest = aux->nano_end - aux->nano_start;
pulse_count = aux->pulse_count_final;
sei();
// Since the AVR has no dedicated floating-point hardware, we need
// to resort to fixed-point calculations for converting nWh/s to W.
// 1W = 10^6/3.6 nWh/s
// value[watt] = 3.6/10^6 * rest[nWh/s]
// value[watt] = 3.6/10^6 * 65536 * (rest[nWh/s] / 65536)
// value[watt] = 3.6/10^6 * 65536 * 262144 / 262144 * (rest[nWh/s] / 65536)
// value[watt] = 61847.53 / 262144 * (rest[nWh/s] / 65536)
// We round the constant down to 61847 to prevent 'underflow' in the
// consecutive else statement.
// The error introduced in the fixed-point rounding equals 8.6*10^-6.
MacU16X16to32(value, (uint16_t)(labs(rest)/65536), 61847);
value /= 262144;
if (rest >= 0)
value += pulse_count*3600;
else
value = pulse_count*3600 - value;
strcpy(message, "pwr ");
break;
}
strcpy(&message[4], measurement->id);
strcpy(&message[36], ":0000000000\n");
i = 46;
do { // generate digits in reverse order
message[i--] = '0' + value % 10; // get next digit
} while ((value /= 10) > 0); // delete it
if ((msg_type == PULSE) && ms) {
strcpy(&message[47], ":0000000000\n");
i = 57;
do { // generate digits in reverse order
message[i--] = '0' + ms % 10; // get next digit
} while ((ms /= 10) > 0); // delete it
}
printString(message);
// printString("\r");
}
