From: Willy Tarreau <email@example.com> To: Richard Genoud <firstname.lastname@example.org> Cc: email@example.com, Thomas Petazzoni <firstname.lastname@example.org>, Antoine Tenart <email@example.com>, Gregory CLEMENT <firstname.lastname@example.org>, Yelena Krivosheev <email@example.com>, Maxime Chevallier <firstname.lastname@example.org>, Nicolas Ferre <email@example.com>, firstname.lastname@example.org Subject: Re: CRC errors between mvneta and macb Date: Mon, 22 Oct 2018 18:34:29 +0200 [thread overview] Message-ID: <20181022163429.GA22826@1wt.eu> (raw) In-Reply-To: <email@example.com> 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, #220.127.116.11 : 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
next prev parent reply other threads:[~2018-10-22 16:35 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 [this message] 2018-10-23 6:56 ` Richard Genoud 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=20181022163429.GA22826@1wt.eu \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.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).