DP83901AV datasheet(36/62 Pages) NSC

36 / 62 page

120 Loopback Diagnostics (Continued)

Since errored packets can be rejected the status associat-

ed with these packets is lost unless the CPU can access the

Receive Status Register before the next packer arrives In

situations where another packet arrives very quickly the

CPU may have no opportunity to do this The SNIC counts

the number of packets with CRC errors and Frame Align-

ment errors 8-Bit counters have been selected to reduce

overhead The counters will generate interrupts whenever

their MSBs are set so that a software routine can accumu-

late the network statistics and reset the counter before

overflow occurs The counters are sticky so that when they

reach a count of 192 (C0H) counting is halted An additional

counter is provided to count the number of packets the

SNIC misses due to buffer overflow or being offline

The structure of the counters is shown below

TLF10469 – 19

Additional information required for network management is

available in the Receive and Transmit Status Registers

Transmit status is available after each transmission for infor-

mation regarding events during transmission

Typically the following statistics might be gathered in soft-

ware

Traffic Frames Sent OK

Frames Received OK

Multicast Frames Received

Packets Lost Due to Lack of Resources

RetriesPacket

Errors CRC Errors

Alignment Errors

Excessive Collisions

Packet with Length Errors

Heartbeat Failure

DP83901AV Datasheet(PDF) 36 Page - National Semiconductor (TI)