More fine grained control of serial baudrate about avr-hal

[explicite]

I will try to start this. Probably I will have lot of questions...

1. This is the generic algorithm mentioned by you let brr = CLOCK::FREQ / (16 * baud) - 1;?
2. Baundrate should be defined as distinct file under generic src like Clock?

[Rahix]

This is the generic algorithm mentioned by you let brr = CLOCK::FREQ / (16 * baud) - 1;?

Yes, it's this code:

avr-hal/avr-hal-generic/src/serial.rs

Lines 56 to 58 in bad9277

	// Value for baudrate register must be calculated based on clock frequency.
	let brr = CLOCK::FREQ / (16 * baud) - 1;
	self.p.[<ubrr $n>].write(|w| unsafe { w.bits(brr as u16) });

In comparison, Arduino upstream uses this code:

  // Try u2x mode first
  uint16_t baud_setting = (F_CPU / 4 / baud - 1) / 2;
  *_ucsra = 1 << U2X0;

  // hardcoded exception for 57600 for compatibility with the bootloader
  // shipped with the Duemilanove and previous boards and the firmware
  // on the 8U2 on the Uno and Mega 2560. Also, The baud_setting cannot
  // be > 4095, so switch back to non-u2x mode if the baud rate is too
  // low.
  if (((F_CPU == 16000000UL) && (baud == 57600)) || (baud_setting >4095))
  {
    *_ucsra = 0;
    baud_setting = (F_CPU / 8 / baud - 1) / 2;
  }

  // assign the baud_setting, a.k.a. ubrr (USART Baud Rate Register)
  *_ubrrh = baud_setting >> 8;
  *_ubrrl = baud_setting;

Baundrate should be defined as distinct file under generic src like Clock?

No, I'd prefer putting that in avr-hal-generic/src/serial.rs as it is very closely tied to it.

Probably I will have lot of questions...

Sure, please don't hesitate asking if anything is unclear!