Intel 82558 Manuale Utente

102

 

To enable the device to receive frames, software must setup the following structure:

1. The SCB general pointer in the SCB should point to the first RFD on the list.

2. The link offset of each RFD in the list should point to the next RFD.

3. The EL bit in the last RFD should be set.

The serial subsystem of the device selects the frames destined for the station according to the 

destination address of the frames passing on the link. A frame is selected if it is at least 6 bytes long 
and its address matches either the individual address, multicast address, multiple IA, or broadcast 

address (promiscuous mode). It transfers the selected frames with their status to the receive FIFO. 

The receive DMA unit transfers the frame from the receive FIFO to host memory under control of 
the receive unit. If discard short frames is enabled, any receive frame shorter than 64 bytes on the 

link (including padding and CRC) will be completely discarded. Although these frames are 

discarded, they are still counted in the short frame counter.

Bit 2

No address match. If this bit is set to 1, the destination address of the received frame does not 
match the individual address, multicast address, or the broadcast address in the filter. For 
example, this bit will be set when the device is in promiscuous mode and the destination address 
does not match any of the other address filtering mechanisms.

Bit 1

IA match bit. When this bit equals 0, it implies that the destination address of the received frame 
matches the individual address. When it is 1, the destination address of the received frame does 
not match the individual address. For example, a multicast or broadcast address will set this bit to 
a 1.

Bit 0

Receive collision (82557 and 82558 only). When this bit is set, it indicates a collision was detected 
during a reception.
TCO indication (82559 and later generation controllers). For the 82559 and later generation 
controllers, this bit no longer reflects collision detection. Instead, it indicates that the device is 
processing a TCO packet. In an environment with a TCO controller where receive to TCO is 
enabled, the controller introduces a new behavior. TCO packets are first posted to the RFA before 
they are transferred back to the TCO controller. In most cases this process is completely 
transparent to the software driver since the RFD that contains the TCO packet is reclaimed. 
However, if header RFDs are being used and the TCO packet size is larger than the header size, 
then the RFD is not reclaimed. In this case, a bad status indication will be posted to memory. The 
bad status indication should be used by the software driver to discard the packet.

0

0

Invalid

0

1

Invalid

1

0

HDS  size

1

1

Total byte count