linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Richard Genoud <richard@sorico.fr>
To: Willy Tarreau <w@1wt.eu>, Richard Genoud <richard.genoud@gmail.com>
Cc: linux-kernel@vger.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Antoine Tenart <antoine.tenart@bootlin.com>,
	Gregory CLEMENT <gregory.clement@bootlin.com>,
	Yelena Krivosheev <yelena@marvell.com>,
	Maxime Chevallier <maxime.chevallier@bootlin.com>,
	Nicolas Ferre <nicolas.ferre@microchip.com>,
	netdev@vger.kernel.org, Andrew Lunn <andrew@lunn.ch>
Subject: Re: CRC errors between mvneta and macb
Date: Tue, 23 Oct 2018 08:56:07 +0200	[thread overview]
Message-ID: <b0ff037c-e32b-6f47-e108-5daefff9b42a@sorico.fr> (raw)
In-Reply-To: <20181022163429.GA22826@1wt.eu>

Le 22/10/2018 à 18:34, Willy Tarreau a écrit :
> On Mon, Oct 22, 2018 at 05:15:21PM +0200, Richard Genoud wrote:
>> After analyzing the ethernet frame on the Davicom PHY's output (pin
>> TX+), I find out that the FCS errors occurs when the ethernet preamble
>> is longer than 56bits. (something like 58 or 60 bits)
>>
>> To say this in another way, instead of having 28 times 1-0 followed by
>> the SFD (10101011), I see 29 or 30 times 1-0 followed by the SFD.
>> (sometimes 29, sometimes 30)
>>
>>
>> Should a longer preamble be considered as an FCS error ? It seems a
>> little harsh since the point of the preamble is to synchronize the frame.
> 
> That indeed seems a bit strange considering that you're not supposed to
> know what is before the preamble so it would very well contain random
> noise looking a lot like alteranted bits.
> 
>> I don't know what the 802.3 standard says about that.
> 
> Just found it :-)
> 
>      https://www.trincoll.edu/Academics/MajorsAndMinors/Engineering/Documents/IEEE%20Standard%20for%20Ethernet.pdf
> 
> Page 132, #7.2.3.2 :
> 
>     The DTE is required to supply at least 56 bits of preamble in
>     order to satisfy system requirements. System components consume
>     preamble bits in order to perform their functions. The number
>     of preamble bits sourced ensures an adequate number of bits are
>     provided to each system component to correctly implement its
>     function.
> 
> So that totally makes sense since the purpose is to enable signal
> detection at the hardware leve, hence the problem definitely is on
> the receiver in your case.
> 
> Willy
> 
Great ! Thanks !
I'll check on the Marvell side

Richard

  reply	other threads:[~2018-10-23  7:03 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-19 15:15 Richard Genoud
2018-10-19 15:44 ` Willy Tarreau
2018-10-22  6:51   ` Richard Genoud
2018-10-22 15:15     ` Richard Genoud
2018-10-22 16:34       ` Willy Tarreau
2018-10-23  6:56         ` Richard Genoud [this message]
2018-10-22 18:19       ` Andrew Lunn
2018-10-23  6:58         ` Richard Genoud
2018-10-23 12:37         ` Richard Genoud

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=b0ff037c-e32b-6f47-e108-5daefff9b42a@sorico.fr \
    --to=richard@sorico.fr \
    --cc=andrew@lunn.ch \
    --cc=antoine.tenart@bootlin.com \
    --cc=gregory.clement@bootlin.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=maxime.chevallier@bootlin.com \
    --cc=netdev@vger.kernel.org \
    --cc=nicolas.ferre@microchip.com \
    --cc=richard.genoud@gmail.com \
    --cc=thomas.petazzoni@bootlin.com \
    --cc=w@1wt.eu \
    --cc=yelena@marvell.com \
    --subject='Re: CRC errors between mvneta and macb' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).