From: Wolfgang Grandegger <wg-5Yr1BZd7O62+XT7JhA+gdA@public•gmane.org>
To: Oliver Hartkopp <socketcan-fJ+pQTUTwRTk1uMJSBkQmQ@public•gmane.org>
Cc: SocketCAN Core Mailing List
<socketcan-core-0fE9KPoRgkgATYTw5x5z8w@public•gmane.org>,
Linux Netdev List
<netdev-u79uwXL29TY76Z2rM5mHXA@public•gmane.org>
Subject: Re: [PATCH net-next v2] candev: allow SJW user setting for bittiming calculation
Date: Tue, 27 Sep 2011 22:04:03 +0200 [thread overview]
Message-ID: <4E822C33.9030207@grandegger.com> (raw)
In-Reply-To: <4E8208B5.4050907-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
On 09/27/2011 07:32 PM, Oliver Hartkopp wrote:
> On 09/24/11 09:22, Wolfgang Grandegger wrote:
>
>> On 09/23/2011 11:32 AM, Pavel Pisa wrote:
>
>>> On base of above analysis, I think that blindly set SJW
>>> on maximum is not good idea. It should be at least limited
>>> to 5% of bit time.
>
>
> (..)
>
>
>>> SJW is more problematic, but may it be use of 2 or 5%
>>> of bittime by default with assurance that zero is
>>> replaced by one, would serve to most people pleasure.
>
>
> (..)
>
>>> But there is still unknown parameter
>>> capacity/length of connected wires so there is still
>>> something left to user consideration.
>>
>> Thanks for your detailed explanation. It clearly shows that adjusting
>> SJW is non-trivial and nothing a normal CAN user should deal with. When
>> adjusting SJW, do you also need to tweek other bit-timing parameters,
>> e.g. tq? I mean, would "ip link set can0 type can bitrate x
>> sampling-point y sjw z" work for your setup or do you need to use the
>> expert mode setting via "ip link set can0 type can tq ..." anyway?
>
>
> Hello Wolfgang,
>
> i double checked a specification where i got my requirement to influence the
> SJW value from. It says (non literally):
>
> "Put the SJW to the highest possible value only reduced by tseg2."
>
> The fact that this requirement might no fit to any CAN setup or may not be in
> best academical shape is not my problem. My requirement is to provide an easy
> way to move the SJW away from it's default value, which is currently
> hard-coded to 1 in the can-dev framework when using it's bittiming calculation
> function.
OK.
> As almost everything is already done (only the provided SJW is not evaluated
> in dev.c) this patch is IMO an valid option to support it. If Joe user can
> tune the sampling point, why should he not be able to influence the SJW if he
> thinks, he knows what he's doing?
>
> Especially as the good working bittiming calculation is not touched in any way
> and the default SJW remains 1 (even if '0' is provided as user input).
Still not sure if it's useful. Anyway, just added my acked-by to your patch.
Thanks,
Wolfgang.
next prev parent reply other threads:[~2011-09-27 20:04 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-22 10:28 [PATCH net-next v2] candev: allow SJW user setting for bittiming calculation Oliver Hartkopp
[not found] ` <4E7B0DE6.9020807-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
2011-09-22 13:07 ` Wolfgang Grandegger
[not found] ` <4E7B331F.3070801-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-09-22 16:26 ` Oliver Hartkopp
[not found] ` <4E7B61C8.8020506-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
2011-09-22 18:10 ` Wolfgang Grandegger
[not found] ` <4E7B7A30.4030707-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-09-22 19:41 ` Oliver Hartkopp
[not found] ` <4E7B8F63.6060108-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
2011-09-23 7:24 ` Wolfgang Grandegger
[not found] ` <4E7C3424.8030406-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-09-23 9:32 ` Pavel Pisa
[not found] ` <201109231132.49976.pisa-/N2ztlQkxE7Ub/6JBqosbQ@public.gmane.org>
2011-09-23 15:50 ` Oliver Hartkopp
2011-09-24 7:22 ` Wolfgang Grandegger
[not found] ` <4E7D8537.8010302-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-09-27 17:32 ` Oliver Hartkopp
[not found] ` <4E8208B5.4050907-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
2011-09-27 20:04 ` Wolfgang Grandegger [this message]
2011-09-24 7:44 ` Wolfgang Grandegger
2011-09-27 20:05 ` Wolfgang Grandegger
2011-09-29 6:14 ` Kurt Van Dijck
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