Baudrate is calculated with SJW in the mix

[attie-argentum]

We've been having some issues with CAN communications between a handful of devices.
I started looking in to how the baudrate is calculated, and it seems to be slightly wrong.

SJW is not actually part of the bit-time calculation, I suspect this has been confused with SYNC_SEG (which is always 1).
The following is from the STM32F72xxx reference manual, but applies to all bxCAN peripherals.

I believe the calculation below should be calcBaudrate = (frequency / (prescaler * (1 + bs1 + bs2))).

STM32_CAN/STM32_CAN.cpp

Lines 707 to 717 in ae6ccad

	while (sjw <= 4) {
	while (prescaler <= 1024) {
	while (bs2 <= 3) { // Time segment 2 can get up to 8, but that causes too small sample-point percentages, so this is limited to 3.
	while (bs1 <= 15) { // Time segment 1 can get up to 16, but that causes too big sample-point percenages, so this is limited to 15.
	int calcBaudrate = (int)(frequency / (prescaler * (sjw + bs1 + bs2)));
	if (calcBaudrate == baud)
	{
	setBaudRateValues(CanHandle, prescaler, bs1, bs2, sjw);
	return;
	}

Separately, to improve interoperability SJW can be increased from the default value of 1 - this will allow the next transition to arrive earlier than the node expects it - up to min(BS2, 4) time quanta.
In many cases, this can be safely set higher than 1 - and in other cases it's even necessary to avoid error frames and wider disruption on the bus.

Please can you let me know if you agree with this, or if you think I'm mistaken?
I'd be happy to prepare a PR to adjust this accordingly.

[pazi88]

You might be right. Please prepare the PR. I'll check it more in detail next week.

[pazi88]

Fixed in #41