For each Nrio network (M2mIoNetwork, NrioNetwork), there is an underlying “actrld” (access control daemon), a low-level process that runs on the JACE host, separate from the station. The actrld polls known Nrio devices (I/O processors) for possible value updates. Each IO device is polled at least 3 times a second, a value fixed in software.
The message response from each IO device is its “IoStatus” value, a concatenated collection of all IO values. See About IO processor updates to IoStatus for related details.
The actrld does a “memory compare” with the previous IoStatus message received from each device. If different, the new IoStatus is passed up to the station’s Nrio driver. When the Nrio network polls for values, it reads from each IO device’s values in its IoStatus slot.
Each I/O processor scans analog inputs (UIs) every 45 ms, storing 6 consecutive readings in a buffer for each input. At this 270 ms cycle, the highest and lowest values in each buffer are discarded, and the four remaining values are averaged. Each UI’s averaged value is then written into the concatenated IoStatus buffer that is read by the actrld process running on the JACE. This entire cycle repeats every 270 ms.
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