127 lines
4.6 KiB
Markdown
127 lines
4.6 KiB
Markdown
FakeEtherCAT Library {#libfakeethercat}
|
|
====================
|
|
|
|
Libfakeethercat is a userspace library which has the same API as the EtherCAT
|
|
master interface library libethercat. Libfakeethercat can be used to spin up
|
|
your RT application in a dry-run mode, without any master configured or slaves
|
|
attached. Furthermore, it is possible to emulate EtherCAT slaves on process
|
|
data level by running two applications back to back.
|
|
|
|
## Supported features
|
|
|
|
Currently, only a very limited subset of libethercat functionality is
|
|
supported:
|
|
|
|
- Creating master and domain instances
|
|
- Activating master, `send`/`receive`.
|
|
- Processing and queuing domains
|
|
- Configuring PDOs
|
|
- Configuring SDOs using `ecrt_slave_config_sdo*`
|
|
|
|
The SDO config does not do anything, but when activating the master the SDO
|
|
config will be dumped into a JSON file.
|
|
|
|
`ecrt_master_state()` and `ecrt_domain_state()` both return states as if the
|
|
bus works without errors. So currently, a bus error cannot be simulated.
|
|
|
|
## How to build
|
|
|
|
[RtIPC](https://gitlab.com/etherlab.org/rtipc) is needed. Simply pass
|
|
`--enable-fakeuserlib` to your `./configure` call and the library will be
|
|
built for you.
|
|
|
|
## How to set up dry run mode
|
|
|
|
### Redirect library loading
|
|
|
|
To avoid recompiling your application, we will use `LD_LIBRARY_PATH` to load
|
|
`libfakeethercat` instead of `libethercat`.
|
|
|
|
```sh
|
|
# pick a location for an empty directory
|
|
export MY_LIB_LOCATION=$HOME/fake_lib64
|
|
# create that directory
|
|
mkdir -p $MY_LIB_LOCATION
|
|
# create a symlink to libfakeethercat
|
|
# assuming SOVERSION is 1
|
|
# debian users, please use /usr/lib/x86_64-linux-gnu/libfakeethercat.so.1
|
|
ln -s /usr/lib64/libfakeethercat.so.1 $MY_LIB_LOCATION/libethercat.so.1
|
|
# use MY_LIB_LOCATION to load libraries first
|
|
export LD_LIBRARY_PATH=$MY_LIB_LOCATION
|
|
# check whether everything is done right
|
|
ldd my_application | grep ethercat
|
|
libethercat.so.1 => /home/vh/fake_lib64/libethercat.so.1 (0x7fa5c590)
|
|
```
|
|
|
|
### Set up FakeEtherCAT Home
|
|
|
|
RtIPC needs a place to store its configuration. Set `FAKE_EC_HOMEDIR`
|
|
environment variable to a path to an empty directory, for instance
|
|
`/tmp/FakeEtherCAT`. `FAKE_EC_NAME` can be set to a useful name of your
|
|
application, default is `FakeEtherCAT`.
|
|
|
|
```sh
|
|
export FAKE_EC_HOMEDIR=/tmp/FakeEtherCAT
|
|
rm -rf $FAKE_EC_HOMEDIR
|
|
mkdir -p $FAKE_EC_HOMEDIR
|
|
```
|
|
|
|
### Spin up your application
|
|
|
|
Now it's time to simply launch your application.
|
|
You will notice that the PDO configuration will be dumped at stderr.
|
|
The path displayed is the path of the RtIPC variable in the following format:
|
|
`$FAKE_EC_PREFIX/$MASTER_ID/$DOMAIN_ID/$ALIAS$POSITION/$PDO`.
|
|
|
|
## How to emulate EtherCAT slaves
|
|
|
|
Let's say you'd like to build virtual EtherCAT slaves to emulate your field.
|
|
Libfakeethercat makes that possible with the help of RtIPC.
|
|
|
|
### Building a simulator
|
|
|
|
Your field emulator simply has to swap the sync manager direction setting
|
|
(EC_DIR_INPUT and EC_DIR_OUTPUT) in ec_sync_info_t.
|
|
Libfakeethercat instances use shared memory, provided by RtIPC,
|
|
to exchange process data.
|
|
The direction setting decides which instance writes and which reads from
|
|
shared memory.
|
|
|
|
For instance, emulating a digital output works in the following way:
|
|
Create another real time application with the same slave information
|
|
as your control application.
|
|
Then, replace all EC_DIR_INPUT with EC_DIR_OUTPUT and vice versa.
|
|
Now, remember to read process data instead of writing it, and vice versa.
|
|
So, your EL2004 digital out will be read by your simulating application
|
|
and has PDO object 0x1600 ff. configured with Sync Manager 2 as EC_DIR_INPUT.
|
|
|
|
[EtherLab](https://gitlab.com/etherlab.org/etherlab) provides
|
|
a convenient way to build an entire simulator using SIMULINK since
|
|
Version 2.4.0.
|
|
Run `web(etherlab_help_path('swap_io.html'), '-helpbrowser')`
|
|
in your MATLAB shell to read more about how to set up a
|
|
Process Data simulator.
|
|
|
|
### Start your application
|
|
|
|
First, do all the steps explained above to run your
|
|
control application in dry run mode.
|
|
Then, in another shell, do the same thing with your simulator,
|
|
but do not remove the `FAKE_EC_HOMEDIR` directory and
|
|
pick another `FAKE_EC_NAME`.
|
|
|
|
Carefully watch the PDO configuration on stderr and compare them. All paths
|
|
configured as output on the control application have to be configured as input
|
|
on your simulator and vice versa.
|
|
|
|
Finally, your control application needs to be restarted
|
|
so it can find the RtIPC variables which contains the process data of the
|
|
simulator.
|
|
|
|
## Environment variables
|
|
|
|
- FAKE_EC_HOMEDIR: Directory for RtIPC bulletin board and SDO json files
|
|
- FAKE_EC_NAME: Will be used for naming RtIPC config and SDO json file
|
|
- FAKE_EC_PREFIX: Prefix for RtIPC variables, useful to run multiple
|
|
simulators side by side.
|