Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Wed, 24 Feb 2010 12:26:35 +0100

Hi

I am glad I put the question mark in the subject. This is not a bug in the 
sequencer but rather in the SNL program. Can you spot it?

Cheers
Ben

On Wednesday 24 February 2010, Benjamin Franksen wrote:
> Hello,
> 
> here is a trivial SNL program I wrote in order to reproduce a
>  misbehaviour that occurs once in a while in one of our production state
>  machines.
> 
> Two state sets communicate via a state variable "x" which is assigned to
>  a bo record and monitored by the program. The master sets x to one, then
>  waits for the slave to reset it to zero. The slave waits for x to become
>  one, then resets it to zero. This all happens in an infinite loop.
> 
> Since there is only one place where x gets set to one (in the master),
>  and one place where it gets reset to zero (in the slave), the assertions
>  in the calls to check() should never fail.
> 
> Your IOC should load this simple database:
> 
>   record(bo,"x") {
>   }
> 
> and this sequencer program:
> 
> program SeqTest
> 
> %{
> #include <assert.h>
> 
> static int check(x) {
>     assert(x);
>     return 1;
> }
> }%
> 
> int done = 0;
> int start = 1;
> 
> int x;
> assign x to "x";
> monitor x;
> 
> ss Master {
>     state idle {
>         when (check(!x)) {
>             printf("Master: work\n");
>         } state work
>     }
>     state work {
>         entry {
>             printf("Master: start slave\n");
>             x = start;
>             pvPut(x);
>         }
>         when (!x) {
>             printf("Master: slave finished\n");
>         } state idle
>     }
> }
> 
> ss Slave {
>     state idle {
>         when (x) {
>             printf("Slave: start work\n");
>         } state work
>     }
>     state work {
>         entry {
>             printf("Slave: enter state work\n");
>         }
>         when (check(x)) {
>             printf("Slave: work done\n");
>             x = done;
>             pvPut(x);
>         } state idle
>     }
> }
> 
> 
> In my tests, the IOC will run for a while but inevitably crash with
> 
> STESTIOC1C: ../seqtest.st:7: test: Assertion `x' failed.
> [1]    8507 abort      ./st.cmd
> 
> This looks like a bug in the sequencer to me. I am testing with
> base-3.14.8.2 and seq-2.0.12.
> 
> (BTW, changing the pvPut calls to SYNC makes no difference.)
> 
> Cheers
> Ben
> 

-- 
"...And you know what incurable diseases do: they invite the quacks and 
charlatans in, who in this case take the form of Software Engineering 
gurus." (Dijkstra, EWD1305)

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System