RE: [PATCH net-next v3 08/14] net: ethernet: oa_tc6: Remove FCS size in RX frame

[Selvamani Rajagopal]

> Subject: Re: [PATCH net-next v3 08/14] net: ethernet: oa_tc6: Remove FCS size in RX
> frame
> 
> 
[..]

 
> 
> More of a question is why request the MAC append the FCS at all.
> You can use it for error correction - but no one every does.
> (A 2k frame has 32-14=18 crc bits for each bit offset which means
> you have an 'average chance' of finding an 18bit error burst that
> will fix every crc error. If you find an 8bit burst error that matches
> the crc error there is a reasonable chance it is what caused the error.
> Single error bursts are the most likely errors and easy to locate.)

My understanding is that in TX side, MAC will pad FCS automatically. RX side, MAC may or may not strip FCS
before passing to the host. I believe our MAC doesn't strip FCS in RX side.

Here is what OPEN Alliance 10BASE-T1x MAC-PHY Serial Interface specification says

7.3 Data Transaction Protocol for Ethernet Frames 
[..]
Ethernet frames are typically transferred from the SPI host to the MAC-PHY without any padding or frame 
check sequence (FCS). The MAC will automatically pad the Ethernet frame to the minimum frame size of 64 
bytes and append a computed FCS
[..]
Similarly, the MAC-PHY will typically strip the FCS from received Ethernet frames prior to transfer to the SPI 
host. However, the Ethernet specification allows the option for the Ethernet frame to be transferred to the 
MAC client with the FCS.


> 
> -- David
> 
> >
> > Andrew
> >