RE: [ethmac] RX MAC

["NewsGroup" <nbase@nbase.com>]

   Hi,

>>
>> 3.
>> in the crc machine , you wrote "Computes a CRC across the data and
compares
>> it with FCS field." I belive a easier way is simple to pass the crc field
>> through the crc machine and simple see that you get the "magic number".
>
>i don't understand,
>what do you mean about "magic number" ?
>from some datasheets i've read, we computes the CRC accross the data and
>compares it with FCS field (CRC received) to make sure that no error in
>frame received.

well this is one way but another way relay on the property of the CRC that
when you computer the CRCof the data AS WELL AS the CRC field you should
ALWAYS get the 32FF of the CRC to show the SAME number and this number is
also called the "magic number".

I don't recall by memorey this number but simple pass the data with the crc
and see the number you get, than pass another packet and you will be
surprise to see that the result is just the same number :-)

one EXTREMLY importent thing but it is also right for the compare way is
that you always start with the right initial value.


>>
>> Also why do you send th 9 MSB bit of the crc ?
>>
>to provide bits needed by host to make hash table for multicast
>addressing.

That is a nice idea !. just wondering what is your application that you need
hashing and for so many address ?

have a nice day

   Illan