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Re: RFC: Enabling ethernet drivers to return FCS in the skb?

To: Linux netdev mailing list <netdev@xxxxxxxxxxx>
Subject: Re: RFC: Enabling ethernet drivers to return FCS in the skb?
From: Rask Ingemann Lambertsen <rask@xxxxxxxxxx>
Date: Mon, 24 Nov 2003 01:05:05 +0100
In-reply-to: <3FC077B1.1050807@xxxxxxxxxxxxxxx>; from greearb@xxxxxxxxxxxxxxx on Sun, Nov 23, 2003 at 01:02:41AM -0800
References: <3FB94311.10004@xxxxxxxxxxxxxxx> <20031119123556.A7622@xxxxxxxxxx> <3FBB8D61.6010106@xxxxxxxxxxxxxxx> <20031120173404.A1538@xxxxxxxxxx> <3FC077B1.1050807@xxxxxxxxxxxxxxx>
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On Sun, Nov 23, 2003 at 01:02:41AM -0800, Ben Greear wrote:

[Intel i82557/8/9 Ethernet chips]

Saving bad frames to memory is controlled by CB_CFIG_SAVE_BAD_FRAMES in byte
6. Saving the FCS to memory is controlled by CB_CFIG_CRC_IN_MEM in byte 18.
See drivers/net/e100/e100_config.h.

> It's less clear what happens when you turn off the FCS generation.  One part 
> of
> the document mentions it gets it from RAM, which I assume means it uses the 
> last
> part of the DMA'd packet???

Yes. The last four octets from the skb will be interpreted as an FCS by
whichever board receives that frame.

> Another explanation of the transmit state machine does
> not mention that you can disable FCS generation...  I'm going to print this 
> out
> and read it again in detail...

There is a bit in the command word of a TX command which disables FCS
generation. I can't find that bit defined in drivers/net/e100/e100.h, so
you'll have to find it in the docs.

-- 
Regards,
Rask Ingemann Lambertsen

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