If you would please refer to the MPC85xx Reference Manuals, you will see that there are configuration registers in the 
DPRAM that specifies whether the CPM will handle the MAC layer CRC.

Specifically, in the MPC8560RM, the CRC hardware assist can be configured as follows:

The transmitter packet pad and CRC append configuration are controlled by the following registers:
- TxBD bit 1 - PAD/CRC
- TxBD bit 5 - Tx CRC
- MACCFG2 bit 29 - PAD/CRC
- MACCFG2 bit 30 - CRC_EN

In the receiver, whenever a CRC error is detected, the RxBD[CR] bit will be set.

Hi,

As per me there are three checksums on different network layers:

1) Ethernet CRC on layer 2
2) IP checksum on layer 3
3) TCP / UDP checksum on layer 4

I'm clear on points 2 & 3 above. Either the hardware can do it or the
io-net (The default is io-net). In case the hardware wants to do it, the
ethernet driver communicates this as mentioned in Network DDK
documentation and as done in devn-i82544: 

ap->capabilities_rx = IFCAP_CSUM_IPv4|IFCAP_CSUM_TCPv4|IFCAP_CSUM_UDPv4;
ap->capabilities_tx = IFCAP_CSUM_IPv4|IFCAP_CSUM_TCPv4|IFCAP_CSUM_UDPv4;

But I'm confused on point 1. So who does it by default? And can we
change this behaviour?

Thanks,

Rajat


----Original Message----
From: Hugh Brown [mailto:hsbrown@qnx.com]
Sent: Thursday, July 03, 2008 5:40 PM
To: drivers-networking
Subject: RE: Ethernet CRC calculation

> When the Ethernet driver advertises itself to io-net, it sets
> the rx and tx capabilities in the io-net advertisement
> structure. You can see this in the devn-i82544.so driver. The
> Ethernet checksum (crc) is always calculated and checked by
> the hardware.
> 
> 
> -----Original Message-----
> From: Rajat Jain [mailto:rajat.jain@infogain.com]
> Sent: Thursday, July 03, 2008 7:46 AM
> To: drivers-networking
> Subject: RE: Ethernet CRC calculation
> 
> 
> Hi,
> 
> A related query. How does the ethernet driver tell the upper
> layers that
> the hardware will do the CRC calculation? In Rx diection? In Tx
> direction? I looked at the Network DDK documentation for this, and it
> only talks about TCP / UDP checksum offloading ... not ethernet
> checksum. 
> 
> Also, can you tell me a sample driver which does offload this CRC
> calculation to hardware? How about devn-mpc85xx?
> 
> Thank You,
> 
> Rajat
> 
> 
> ----Original Message----
> From: Hugh Brown [mailto:hsbrown@qnx.com]
> Sent: Thursday, July 03, 2008 5:09 PM
> To: drivers-networking
> Subject: RE: Ethernet CRC calculation
> 
>> Depending on the driver, it is either the Ethernet hardware
>> or the upper layers. The drivers don't perform any CRC
>> calculations on the data. If the hardware can perform the
>> checking and it is enabled to do so, then the hardware will
>> perform the calculation and checking.
>> 
>> 
>> -----Original Message-----
>> From: Daniel Rodrick [mailto:daniel.rodrick@gmail.com]
>> Sent: Thursday, July 03, 2008 5:43 AM
>> To: drivers-networking
>> Subject: Ethernet CRC calculation
>> 
>> Hi,
>> 
>> In io-net model, who is responsible for calculating (Tx) / validating
>> (Rx) the ethernet CRC in ethernet frames? Is it the ethernet driver
>> or the higher layers? 
>> 
>> TIA,
>> 
>> Dan
>> 
>> _______________________________________________
>> Networking Drivers
>> http://community.qnx.com/sf/go/post9993
>> 
>> 
>> _______________________________________________
>> Networking Drivers
>> http://community.qnx.com/sf/go/post9996
> 
> 
> _______________________________________________
> Networking Drivers
> http://community.qnx.com/sf/go/post9998
> 
> 
> _______________________________________________
> Networking Drivers
> http://community.qnx.com/sf/go/post10001