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From: "Thomas Wagner" <>
To: "'Marc Kleine-Budde'" <>
Cc: <>
Subject: RE: Write canfd_frame to can interface
Date: Thu, 29 Jul 2021 14:02:34 +0200	[thread overview]
Message-ID: <00a601d78471$9e6f3ca0$db4db5e0$> (raw)
In-Reply-To: <>

Hello Marc,

On 2021-07-29 12:55, Marc Kleine-Budde wrote:
> On 29.07.2021 12:03:56, wrote:
>> Shouldn't the error only be returned if the
>> canfd_frame I pass has more than 8 bytes when the interface is not in
>> FD-mode?
> A CAN-2.0 frame with 8 bytes is something different than a CAN-FD frame
> with 8 bytes. The kernel uses the length of the frame to decide if it is
> a CAN-2.0 or CAN-FD frame. If your CAN controller has switched CAN-FD
> off, it cannot send CAN-FD frames, thus you get an error.
> Does that make sense?


I see how a CAN-2.0 frame with 8 bytes differs from a CAN-FD frame with
8-bytes, but when I receive into a canfd_frame I can't differentiate like that
anymore. In userspace an 8B CAN-2.0 frame and an 8B CAN-FD frame look just
the same, no matter the interface running with FD on or off.

... which is wrong as I just noticed. Paying attention to the actual bytes read
by the socket I can see the 16 vs. 72B that make up a can_frame vs. a
canfd_frame respectively. Even when always writing into a canfd_frame.
The same differentiation I must make when sending...

Thanks for the quick reply!

Best regards
Thomas Wagner

  reply	other threads:[~2021-07-29 12:02 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-29 10:03 Write canfd_frame to can interface thomas
2021-07-29 10:55 ` Marc Kleine-Budde
2021-07-29 12:02   ` Thomas Wagner [this message]
2021-07-29 12:14     ` Marc Kleine-Budde

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