On 26.02.2021 15:26:33, Torin Cooper-Bennun wrote: > On Fri, Feb 26, 2021 at 03:00:54PM +0100, Marc Kleine-Budde wrote: > > https://github.com/hartkopp/M_CAN-User-Manual-History > > Great, thanks. I can see this also sits in the linux-can repo which is > handy. > > > > Note: With CAN FD an external counter is required for timestamp > > > generation (TSS = “10”) > > > > I suggest to check on the tcan hardware, what's really in the register. > > I've just verified that internal timestamping works on the TCAN4550 (in > both RX FIFO and TX event FIFO), with FD and BRS both enabled. The > 16-bit timestamps are generated specifically from the nomimal bit times, > and you can prescale up to 16x. \o/ NICE! \o/ > 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. Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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