Arduino for STM32

One thing that might help is to make sure the Preferences Show detaild (Build) information are unchecked.
Otherwise even for files that are prebuilt one line of information about not recompiling is printed

Problem with analog inputs on this specific pin PC4 or on all analog input pins ?

The settings to the ADC is handled by the analogRead function.

I am using a Nucleo 64 L476RG card, connects the A3 pin, dac out, to PC4.
STM32dino v2, select board Nucleo 64 and partnumber Nucleo L476RG
Arduino serial monitor

pinMode(PC4, INPUT); is not needed, analogRead does the pin configuration.

check the input voltage with a multimeter.

Following code ...

Should work, can you show circuit diagram and complete code ?

It also seems that the BluePill variant uses PB6 and PB7 as default I2C

First try the "Examples/Wire/i2c_scanner" sketch to check the basic i2c communication and that your sensor board is recognised.

The TIC circuit, HC4046 plus D1, R1 and C1 measures the phase relation between the oscillator divided down to 1MHz and the PPS1. The output voltage over C! that is then read by the ADC is an increasing (not really linear, more exponentially increasing so the initial slope is more or less linear ...

You can check the RCC_CR and RCC_PLLCFGR to see what clocks are running and what source is selected for the PLL


Serial.printf("RCC_CR 0x%08X \n", RCC->CR);
Serial.printf("RCC_CFGR 0x%08X \n", RCC->CFGR);
Serial.printf("RCC_PLLCFGR 0x%08X \n", RCC->PLLCFGR);


Details of these regsters are ...

Thats double, 64 bits with range 2.22507385850720138e-308 to 1.79769313486231571e+308 (normalized values) that is seventeen decimal place approx and its not hardware accelerated, so good for accuracy with limited use.
The STM32F4 (CortexM4F) has single precision hardware float with range 1 ...

Having to guess what your code looks like makes it hard to give any help.

How was the other serial ports used, initiated and what was the result ??