Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Mon, 5 Oct 2009 22:47:18 +0200

On Montag, 5. Oktober 2009, Andrew Johnson wrote:
> I suspect it would be a good idea to try and get the the SNL compiler to
> issue a warning whenever it sees someone calling pvPut() on a variable
> which has a monitor on it, since this is IMHO an unsafe practice.

It is not if you do it right. I have never observed any problems with it. 
You just have to make sure that the value your SNL program writes is 
different from what the outside writes. Typically I reserve some value 
(usually 0) for 'done' (a.k.a. 'idle'). The outside is not allowed to write 
this value (this can be enforced using yet another record). Then I have 
some SNL code like

int cmd;
assign cmd to "whatever";
monitor cmd;

state idle {
    when (cmd==DO_SOMETHING) {
        setup_execution();
    } state first_intermediate_state
    ...
    when () {
    } state done
}
...intermediate states...
state done {
    when ... {
        cmd = 0;
        pvPut(cmd);
    } state idle
}

The advantage is that I don't need event flags which I always found to be 
unreliable.

Cheers
Ben

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System