Wolfgang Grandegger wrote: > On 08/13/2010 08:55 AM, Heinz-Jürgen Oertel wrote: >> Am Mittwoch, 11. August 2010 17:59:17 schrieb Marc Kleine-Budde: >>> Bit timing parameters for flexcan with 24.576000 MHz ref clock >>> nominal real Bitrt nom real SampP >>> Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP >>> Error CAN_CTRL 1000000 40 8 8 8 1 1 983040 1.7% 75.0% >>> 68.0% 9.3% 0x003f0007 1000000 81 4 4 3 1 2 1024000 2.4% >>> 75.0% 75.0% 0.0% 0x011a0003 1000000 122 2 3 2 1 3 >>> 1024000 2.4% 75.0% 75.0% 0.0% 0x02110001 >>> >> >> Hello Wolfgang, Marc, >> I was not aware that the clock is 24.576000 MHz, always thought 24.000000. >> It is often the case that the crystal clock is chosen to get a perfect bit >> rate for UARTS, not for CAN. But a UART frame, having only 10 bits, can live >> with a much higher deviation from the nominal bit clock. > > Yep, a good CAN clock has a frequency of (n * 8) MHz. > >> I see that you typical use a sample point at 75%. >> CANopen has a "Recommended location of sample point" at 87.5%. (CiA 301). > > But not at 1 MHz!? We use: > > http://lxr.linux.no/#linux+v2.6.35/drivers/net/can/dev.c#L82 > > Please correct me if I'm wrong.
See the screenshot in the other mail. Seems the CIA has modified their recommendation. Marc -- Pengutronix e.K. | Marc Kleine-Budde | Industrial Linux Solutions | Phone: +49-231-2826-924 | Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |
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