|On Jan 31, 2019, at 10:08 AM, Mark Rivers via Tech-talk <firstname.lastname@example.org> wrote:|Ø
Then, if am correct, this means I will require 2 records for each command, right?
One (for ex. stringout) to send the command and other (ex. stringin) to capture the responses with I/O Intr.
In my drivers I generally use 2 records, one for the Set (ao, longout, stringout, mbbo, etc.) and one for the Get (ai, longin, stringin, mbbi, etc.).
If you write an asynPortDriver then your records would normally not be stringout and stringin, they would be the records hold the underlying data type of the property (ao/ai, bo/bi, mbbo/mbbi, stringout/stringin only for string parameters). The driver formats these into strings for Sets and parses the response for Gets.
It is possible to use a just an output record if the record has the info tag asyn:READBACK=1. Then the output record value is updated with a Get operation. I think it’s generally better to use 2 records since you then have independent error status of the Set and Put operations. You can also see on the OPI display if the Get value does not match the Set value, because of things like out-of-bounds, truncation/rounding, etc.
If the second option is also not possible, then 4 records may be necessary for each property:
- For SET response with IO Intr
- For GET response with IO Intr
You really don’t need the SET response record because that information be set in the STAT and SEVR of the SET record.
Perhaps, but I don’t see how the SET command would get its response — the network input port/stream is tied up by the read thread, right? Or do SET and GET commands use separate ports? Also, if SET commands can be ’slow’ then their responses woud be better handled by a read thread.
You don’t need the GET command record, that string is constructed in the driver.
I’ve found it useful to have a ’trigger readback’ record. That makes it easy to control the rate at which readbacks are requested.
So my $0.02 is that it’s best to have four records. Although perhaps s single ’trigger readback’ record could be used to request a number of responses.