RE: [ethmac] magic number, compatibility problem?!

["Illan Glasner" <iglasner@zumanetworks.com>]

25-Feb-02

Hi,

   while for checking you simple pass all the data inculding the packet crc into the equation and see that you get the magic number or not to detrmine if the packet was curropted or not.

when appending/generating the result fo the 32 FF of the "pure data" need to be bit swap and invert and only than append to the data as the data crc field.

there is no two way to do it only the above one.

IF you will not do the swap/invert you will get a crc zero in the checker BUT THIS IS NOT A LEGAL WAY.

have a nice day

   Illan

-----Original Message-----
From: jcwh@sina.com [mailto:jcwh@sina.com]
Sent: Monday, February 25, 2002 1:06 AM
To: ethmac@opencores.org
Subject: RE: [ethmac] magic number, compatibility problem?!


in tx module,
if a 32-bit CRC need to be generated and transmitted.
when the CRC is generated, does the data pass the FCS in bit swap?
when the CRC is appended, does the data is transmitted in bit swap?

in the file eth_txethmac.v, the writer shoud be one of the three authors.
it looks that CRC is generated and transmitted in a bit swap way:
"
...
  if(StateFCS)
    MTxD_d[3:0] = {~Crc[28], ~Crc[29], ~Crc[30], ~Crc[31]};     // Crc
...
assign Data_Crc[0] = StateData[0]? TxData[3] : StateData[1]? TxData
[7] : 1'b0;
assign Data_Crc[1] = StateData[0]? TxData[2] : StateData[1]? TxData
[6] : 1'b0;
assign Data_Crc[2] = StateData[0]? TxData[1] : StateData[1]? TxData
[5] : 1'b0;
assign Data_Crc[3] = StateData[0]? TxData[0] : StateData[1]? TxData
[4] : 1'b0;
...
"

i don't know in the normal ethernet controller, how the crc is generated 
and transmitted, in bit swap way or a normal way?

this confused me, and i wonder whether the compatibility problem will 
result here.

maybe i did't say clearly last time. i hope i make you know what i am 
thinking this time.

best regards.
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