Re: can, tcan4x5x: look to merge rpi support into rpi kernel tree

Torin Cooper-Bennun
2021-02-26T16:15:36Z

On Fri, Feb 26, 2021 at 05:01:35PM +0100, Marc Kleine-Budde wrote:
> > Is timestamp-wrapping a concern for rx-offloading?
>
> No, as long as you provide a proper u32 timestamp, which means wrap
> around at 0xffffffff to 0x0. As the tcan4x5x has only a 16 bit
> timestamp, shift it to full 32 bit, like this:
>
> https://elixir.bootlin.com/linux/v5.11/source/drivers/net/can/flexcan.c#L805
>
> On the mcp with true 32 bit timestamp there's a wraparound every 107
> seconds at 40 MHz external clock (0xffffffff / 40000000).
>
> The tcan has the TSS.TCP as a prescaler and increments in bit time,
> which is 5MHz max. This results in a wrap around every 13ms (0xffff /
> 5000000) with a prescaler of 1. With a prescaler of 16, you can increase
> this to 209ms (0xffff / 5000000 * 16), which gives an accuracy of 2
> bytes.

Nice, thank you, that all sounds good. I'll get to work. :)

--
Regards,

Torin Cooper-Bennun
Software Engineer | maxiluxsystems.com