Генератор зла » Пн дек 16, 2013 12:56 pm
Reply Timeout
Many DAServers include Reply Timeout parameters (the same as the Reply Timeout parameter in the legacy I/O Servers). If the DAServer receives a single transaction message timeout, the topic is placed in Slow Poll mode.
Normally, a larger number (longer time) is used for slow-action end devices – for example, communication to the end devices over a radio modem network. However, the longer the timeout period is, the longer the next request has to wait its turn to be executed.
This often causes different problems, especially when it comes to writing data. For example, if the client is poking a block of data in a script, each write command will be pending against the Reply Timeout to receive the confirmation from the PLC. While in pending all the rest of the write requests will be sent to a write queue. Since only 10 (30 for the newer release of the DAServer) queue spaces are reserved, when the queue is full, any the new write requests are rejected and the following error is generated in the logger:
10 outstanding write already, refused.
When this happens, the end user should consider options such as slowing down the poking rate; using shorter Reply Timeout periods (so it will get timeout quicker and get on with the next transaction), increasing the reaction time of the network- or end-devices.
The end users need to use their own judgments and tweak this setting to fit their own situation.
Vita est dolor.