9000

82 Chapter 5

Troubleshooting

HSC FDDI/9000

In order to achieve the best single card performance, the HSC

FDDI/9000 product has set the Transmit Threshold to an aggressive

value. The Transmit Threshold is set so that transmission will begin

after 1024 bytes are in the transmit FIFO.

The HSC FDDI product supports four levels of Transmit Threshold.

These four levels are modiﬁed via the -S option of the lanadmin

command, as follows:

lanadmin -S TransmitThreshold PPA

where TransmitThreshold can be one of the following values:

1024 is most aggressive (this is the default value)

2048 is somewhat aggressive

3072 is somewhat conservative

4096 is conservative

In all of the cases above, after setting the TransmitThreshold mode as

speciﬁed, the lanadmin command will echo the current speed of the

interface; this output may be ignored. The following example shows

output for 100 Mbits/s operation:

old speed= 100000000

new speed= 100000000

After issuing lanadmin -S, you must wait at least 5 seconds before

attempting to use the speciﬁed network interface.

HSC FDDI transfers data from memory on the card to memory on the

host via Direct Memory Access (DMA) operations. By default, the data

transfer burst size for DMA operations is 128 bytes. If the HSC FDDI

card is installed in an HSC bus that is shared with other HSC devices

(for example, an HSC SCSI card and other network cards), the bus

competition among those devices may be increased. If setting the

Transmit Threshold value with the lanadmin command results in

increased “receive overrun” errors, it may be because of the HSC bus

competition with other devices. To reduce the receive ovverun errors,

change the data transfer burst size from 128 bytes to 32 bytes with the

special command lanadmin -S 0. Note that if you issue the lanadmin

-S 0 command, any subsequent setting of the Transmit Threshold value

with the lanadmin command restores the data transfer burst size to 128

bytes.