Improving RTC accuracy

[michpro]

If anyone is interested in improving the accuracy of their RTC, I have created a piece of code that allows you to calibrate the RTC using the PPS signal from a GPS receiver: link
It works with GD32F30x, GD32F50x and GD32F10x cores.

[maxgerhardt]

Nice! May I ask why

https://github.com/michpro/arduino_libraries/blob/a7b9e1069da749b89db9cf722f195afb6c03ccc4/GD32_RTC_Calibration/src/RTCCalibration.cpp#L138-L139

is using direct GD32 calls instead of the Arduino abstraction

attachInterrupt(digitalPinToInterrupt(ppsPin), ppsIrqHandler, RISING);

? Is that not working in the core?

[michpro]

Direct GD32 calls are used to reduce FLASH usage.
For example, for GD32F303CC and -Os optimization:

• when we use attachInterrupt(), we have: attachInterrupt() (184 bytes) + begin() (44 bytes) = 228 bytes
• for direct calls: only begin() = 136 bytes

The difference is 92 bytes.

Of course, this gain will decrease if we need other attachInterrupt() calls elsewhere in the programme.

[maxgerhardt]

Mhm, given the implementation of attachInterrupt() as being pretty much that block of code, that's surprising to me. (

ArduinoCore-GD32/cores/arduino/WInterrupts.cpp

Lines 23 to 45 in 9f1c9f1

	void attachInterrupt(pin_size_t pin, voidFuncPtr callback, PinStatus mode)
	{
	exti_trig_type_enum it_mode;
	PinName pinname = DIGITAL_TO_PINNAME(pin);
	switch (mode) {
	case CHANGE :
	it_mode = EXTI_TRIG_BOTH;
	break;
	case FALLING :
	case LOW :
	it_mode = EXTI_TRIG_FALLING;
	break;
	case RISING :
	case HIGH :
	it_mode = EXTI_TRIG_RISING;
	break;
	default:
	it_mode = EXTI_TRIG_RISING;
	break;
	}
	gpio_interrupt_enable(GD_PORT_GET(pinname), GD_PIN_GET(pinname), callback, it_mode);
	}

).

But thanks for the explanation.