Re: Queries on CAN frame work

[Marc Kleine-Budde <mkl@pengutronix.de>]

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Hello Srinivas Neeli,

On 13.01.2022 18:14:06, Srinivas Neeli wrote:
> This mail is regarding to understand more on CAN Frame work for CANFD
> networks.

let's discuss this on the CAN mailing list (Cc'ed). Feel free to
subscribe (http://vger.kernel.org/vger-lists.html#linux-can). Please
post non HTML mail.

> Recently we did few experiments with our CANFD network. Stuff error
> observed with different Nominal and Dataphase prescaler configuration
> values, which we get from the frame work.
> 
> 
> For lower baud rates separate prescalers are working good, but when we
> switch to high baud rates(like 4Mbps and 5Mbps) observed the BUSOFF
> state(Due to stuff errors) on IP(Xilinx).
> 
> With shared prescaler(low prescalers) we are not seeing the issue..
> 
> In Iso spec also mentioned to avoid tolerance, we have to maintain
> common TQ for Nominal and Data phase.
> 
> Spec: ISO 11898-1:2015(E)  page no :50
> 
> " If the same time quantum length is used in the nominal bit time and
> in the data bit time and the positions of the sample points in the
> nominal bit time are the same in all CAN nodes of a network, then
> optimum clock tolerance is accomplished for networks using FD frames."
> 
> CIA:
> https://can-newsletter.org/uploads/media/raw/f6a36d1461371a2f86ef0011a513712c.pdf
> 
> From above CAN-newsletter also suggested the same in recommendation 2 and 3.
> 
> Recommendation 2: Set the BRPA bit-rate prescaler equal BRPB
> Recommendation 3: Choose BRPA and BRPD as low as possible
> 
> Is there any possibility in framework to use shared prescalars for Nominal and Dataphase?.
> 
> One more question. How to calculate TDCO ?, is there any generic formula for this ?.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
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