This parameter is designed to reduce #COMs when
using dialup or scheduled devices. The #COM is often a result of
how tags are blocked together in the IOServer.
This is the global INI setting. This setting is
allowed at a per device level by:
[<unitname>] CacheOptMode = x
By default, the IOServer only searches for tag
data requests to be within or equal to a single cached tag set; for
example, cache has tag address points 1 to 10, and then 11 to 20,
and a request wants addresses 5 to 6, this is permitted. If,
however, the request was for items 9 to 11, the system would not
return a match and would request a read from the driver. For a
disconnected dialup unit, this would cause a #COM or #WAIT.
CacheOptMode Values are:
1 - First come first served -
Tells the IOServer to search through cached points looking for the
data, once it is found return.
2 - Scan cache for latest entries
- Forces the scan to look through cached items to find data which
is the MOST recent.
4 - An incomplete match is OK -
Tells the system that if some items match and some are not found,
to consider this OK.
+8 - Allow behavior on all
devices, by default the settings above only apply to remote
units.
+16 - Allow written data not to
remove cache item and update value on return, e.g. 1 to 10 in the
cache, write to 8. The default behavior would be to remove the
whole cache item so that a fresh read of 1 to 10 would be needed on
a write to 8. With +16 added, then 1 to 10 stays in the cache, and
item 8 would be updated on the REPLY from the driver.
For dialup devices, CacheOptMode=1 covers the
majority of needs.