Re: [etherlab-users] how to get slave count from userspace ?

[Sebastien Blanchet]

Hi Gavin,

You are right:
For way #1, if I use ecrt_master() instead of ec_master(), it works.

Anyway I will use the way #2, as you told me.

thank for you help
---
sebastien

On 07/28/2014 07:54 AM, Gavin Lambert wrote:

On 26 July 2014, quoth Sebastien Blanchet:

I would like to know which is the right way to get the number of slaves
on the EtherCAT bus in a usespace program.

I have tried 3 ways:

// way #1:
      ec_master_info_t masterInfo;
      ec_master_t* master = ecrt_request_master(0);
      ec_master( master, &masterInfo );

      // the answer should be in masterInfo.slave_count
      // but it does not work because the compiler says
      //"error: invalid use of incomplete type 'struct ec_master'"

That's because the API call is "ecrt_master", not "ec_master".  If you
correct that, then this should work, but it's not the most efficient method.

// way #2
      ec_master_state_t state;
      ec_master_t* master = ecrt_request_master(0);
      ecrt_master_state( master, &state );

      // it seems to work,
      // the answer is in state.slaves_responding

This is the correct method.

// way #3  (very ugly)
      ec_slave_info_t dummySlaveInfo;
      int slave_count = 0;
      ec_master_t* master = ecrt_request_master(0);

      while (!ecrt_master_get_slave( master, slave_count,
&dummySlaveInfo)) {
        slave_count++;
      }

Don't do this (unless you actually want to keep each slave's info).
Remember that if you're using the usermode lib, each time you call a master
API you are making a user->kernel->user transition, which will cause a
performance hit.  While it doesn't really matter at this point (since you're
still pre-realtime) making excessive API calls is not a good habit to get
into.

--
Sebastien BLANCHET
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