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fix analogReference() #643

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fix analogReference() #643

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27 changes: 7 additions & 20 deletions megaavr/cores/dxcore/wiring_analog.c
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@
*/


#include "avr/io.h"
#include "wiring_private.h"
#include "pins_arduino.h"
#include "Arduino.h"
Expand Down Expand Up @@ -390,12 +391,8 @@ inline __attribute__((always_inline)) void check_valid_resolution(uint8_t res) {

/* Ex Version*/
void analogReference(uint8_t mode) {
check_valid_analog_ref(mode);
if (mode > 7)
mode &= 7;
if (mode != 1 && mode != 3) {
ADC0.CTRLC = mode;
}
check_valid_analog_ref(mode); // does all the checking
ADC0.CTRLC = (ADC0.CTRLC & ~(ADC_REFSEL_gm)) | (mode & (ADC_REFSEL_gm));
}
/* Ex Version*/
inline uint8_t getAnalogReference() {
Expand Down Expand Up @@ -699,16 +696,8 @@ inline __attribute__((always_inline)) void check_valid_resolution(uint8_t res) {
return _analog_options & 0x0F;
}
void analogReference(uint8_t mode) {
check_valid_analog_ref(mode);
#if defined(STRICT_ERROR_CHECKING)
if (mode > 7) return;
#else
mode &= 7;
#endif
if (mode != 1 && mode != 3) {
ADC0.CTRLC = mode;
}
// Uh? Is that it? That was, ah, a tiny bit simpler.
check_valid_analog_ref(mode); // does all the checking
ADC0.CTRLC = (ADC0.CTRLC & ~(ADC_REFSEL_gm)) | (mode & (ADC_REFSEL_gm));
}
inline uint8_t getAnalogReference() {
uint8_t r = ADC0.CTRLC & ADC_REFSEL_gm;
Expand Down Expand Up @@ -950,10 +939,8 @@ inline __attribute__((always_inline)) void check_valid_resolution(uint8_t res) {
######## ## ## ## ######## ######## ## ######## ######## */

void analogReference(uint8_t mode) {
check_valid_analog_ref(mode);
if (mode < 7 && mode != 4) {
VREF.ADC0REF = (VREF.ADC0REF & ~(VREF_REFSEL_gm))|(mode);
}
check_valid_analog_ref(mode); // does all the checking
VREF.ADC0REF = (VREF.ADC0REF & ~(VREF_REFSEL_gm))|(mode & (VREF_REFSEL_gm));
Comment on lines +942 to +943

@k-takata k-takata Sep 7, 2026

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It seems check_valid_analog_ref() checks only at compile time.
Isn't it better to keep runtime checking? E.g.:

Suggested change
check_valid_analog_ref(mode); // does all the checking
VREF.ADC0REF = (VREF.ADC0REF & ~(VREF_REFSEL_gm))|(mode & (VREF_REFSEL_gm));
check_valid_analog_ref(mode);
mode &= VREF_REFSEL_gm;
if (mode < 7 && mode != 4) {
VREF.ADC0REF = (VREF.ADC0REF & ~(VREF_REFSEL_gm))|(mode);
}

@wke67 wke67 Sep 9, 2026

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I agree, runtime checking is a good thing - but only if you can return an error code, which you can not do here.
The runtime checking is done partially by masking the mode value with VREF_REFSEL_gm, I think that is good enough. BTW, the hard part in debugging this error was to understand why the function did not modify the register, only the source code could tell.

}

int16_t analogRead(uint8_t pin) {
Expand Down
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