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APM: added board_voltage() function

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This commit is contained in:
Andrew Tridgell 2012-03-01 15:21:32 +11:00
parent 1e8d98cdda
commit b20084af7d
1 changed files with 33 additions and 0 deletions
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33
ArduPlane/system.pde
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@ -565,3 +565,36 @@ void flash_leds(bool on)
digitalWrite(A_LED_PIN, on?LED_OFF:LED_ON);
digitalWrite(C_LED_PIN, on?LED_ON:LED_OFF);
}
#ifndef DESKTOP_BUILD
/*
* Read Vcc vs 1.1v internal reference
*
* This call takes about 150us total. ADC conversion is 13 cycles of
* 125khz default changes the mux if it isn't set, and return last
* reading (allows necessary settle time) otherwise trigger the
* conversion
*/
uint16_t board_voltage(void)
{
static uint16_t vcc = 5000;
const uint8_t mux = (_BV(REFS0)|_BV(MUX4)|_BV(MUX3)|_BV(MUX2)|_BV(MUX1));
if (ADMUX == mux) {
ADCSRA |= _BV(ADSC); // Convert
uint16_t counter=4000; // normally takes about 1700 loops
while (bit_is_set(ADCSRA, ADSC) && counter) // Wait
counter--;
if (counter == 0) {
// we don't actually expect this timeout to happen,
// but we don't want any more code that could hang
return vcc;
}
uint32_t result = ADCL | ADCH<<8;
vcc = 1126400L / result; // Read and back-calculate Vcc in mV
} else {
ADMUX = mux; // switch mux, settle time is needed
}
return vcc; // in mV
}
#endif