12.0 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 ST-NIC 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 ST-
NIC misses due to buffer overflow or being offline.
The structure of the counters is shown below:
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
Retries/Packet
Errors: CRC Errors
Alignment Errors
Excessive Collisions
Packet with Length Errors
Heartbeat Failure
TL/F/11157 – 20
40
Obsolete