| The Softhub server used by the SQDNET
driver does not support multiple outstanding requests to a single
device. Therefore, this has been prevented by the Citect driver by
ensuring that the MaxPending driver parameter is 1 (one) by default
for a port, and multiple logical Citect devices with the same
physical address are on the same port.
This can lead to some performance problems in the situation
where multiple devices are placed on the same logical port. Firstly
data throughput is reduced because the one outstanding request
allowed for the port must be shared between several devices.
Secondly, if one of the devices times out, then the data requests
to the other devices are delayed considerably because of the
combination of the timeout handling and the restriction of
MaxPending being set to 1 (one). |
