The open Master Hearing Aid Forum

Posted: **Thu Aug 12, 2021 9:35 am**

Hi :)

I've been playing around a bit with example6.cpp from the Developer manual to get to know how to work with AC variables. I've managed to create an AC variable by declaring it as member of the class example6_t:

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comm_var_t test_ac;

And setting up data_type, num_entries, stride and data as well as register it in the constructor.

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test_ac.data_type = MHA_AC_FLOAT;
test_ac.num_entries = 2;
test_ac.stride = 1; 
test_ac.data = test;

ac.insert_var( ac.handle, "testac", test_ac );

The float variable test is filled in the process function.

Now I was wondering how to get an AC variable from an other plugin. For this I've put the original plugin example6 before my own plugin:

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mha.algos=[ example6 steffencov acmon ]

The plugin example6 creates an AC variable called "example6_rmslev" which I tried to catch in my own plugin steffencov using

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 ac.get_var(ac.handle, "example6_rmslev",&new_ac_var);

and register it as a new AC variable to test if it worked:

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ac.insert_var( ac.handle, "test3", new_ac_var );

And it did. The AC variable example6_rmslev had the same value as test3. Then I wanted to try the same thing, but instead of having example6 switched before my own plugin, I've used lsl2ac to catch e.g. the clock corrections of a test stream e.g.

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    ac.get_var(ac.handle, "SimpleStream_tc",&new_ac_var);

and

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    ac.insert_var( ac.handle, "test3", new_ac_var );

But this did not work - in this case test3 is just an empty 0x1 variable:

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# complete list of variables
# vector<string> (monitor)
mha.acmon.varlist = [SimpleStream SimpleStream_new SimpleStream_tc SimpleStream_ts test3]

# variable dimensions in AC space
# vector<string> (monitor)
mha.acmon.dimensions = [1x480 1x1 1x1 1x1 0x1]

Do you know why this could be?
I will attach my (rather messy) C++ code and the configuration I've used for testing this.

Best regards,
Steffen

Posted: **Thu Aug 19, 2021 12:39 pm**

I found a second way to access the value of an AC variable from another plugin (in this case rmslevel), using:

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 mha_wave_t* example6_t::process(mha_wave_t* wave)
{
    poll_config();
    store_ac_single = MHA_AC::get_var_float(ac,"rmslevel_level");
    return wave;
}

store_ac_single is a float variable, which means I can simply do stuff like this:

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 store_ac_single = store_ac_single+1;

This works also with vectors (when setting nchannels_in = 2 rmslevel_level will be a 1x2 vector):

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# vector<float> (monitor)
mha.acmon.rmslevel_level = [0.00896696746 5.30756188e-05]

In this case one can declare a vector which should later hold the values

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    std::vector<float> store_ac_single;

and use:

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    store_ac_single = MHA_AC::get_var_vfloat(ac,"rmslevel_level_db");

to store store them. The problem here is that this does not work with the AC vars exported from lsl2ac.

When trying to do the same to an LSL stream, e.g. trying to catch the values of a time series using

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 store_ac_single = MHA_AC::get_var_vfloat(ac,"Mobi_EEG_030105");

one gets:

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mha [1] MHA Error: (mhapluginloader) Error in module "mhachain:mhachain":
(mhapluginloader) Error in module "steffencov:steffencov":
(mha_algo_comm) Algorithm communication variable Mobi_EEG_030105 has unexpected data type 4

although acmon says it's a vector<float>, not sure if I misunderstand something here.

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# vector<float> (monitor)
mha.acmon.Mobi_EEG_030105 = [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]

Using

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 store_ac_single = MHA_AC::get_var_float(ac,"Mobi_EEG_030105_tc");

(float instead of vfloat)

Works just fine since it is a scalar value.

So my question would be how do I ready in the AC variable time series values which are not scalars but vectors?

Minimal example will be attached.

Posted: **Sun Aug 29, 2021 11:17 am**

steffendasenbrock wrote: ↑
Thu Aug 12, 2021 9:35 am
Then I wanted to try the same thing, but instead of having example6 switched before my own plugin, I've used lsl2ac to catch e.g. the clock corrections of a test stream e.g.
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    ac.get_var(ac.handle, "SimpleStream_tc",&new_ac_var);
    ac.insert_var( ac.handle, "test3", new_ac_var );
But this did not work - in this case test3 is just an empty 0x1 variable:

The above code needs to execute every time prepare() or process() executes.

Please see the developer manual, section 3.4 "Communication between algorithms", especially 3.4.1 "Detailed Description", and there especially the best practices following the sentence "As a developer of openMHA plugin(s), please observe the following best practices in plugins using AC variables".

As you can see from the best practices, you should really not do it like in your example because there you are violating the best practice "memory used for storing AC variable values is allocated and owned by the publishing plugin". But I understand that you are only doing this wile learning about AC variables and will use a safer approach in practice.

Posted: **Tue Sep 07, 2021 2:01 pm**

Thank you for your answer!

executing the code in process() as well as in prepare() solved the issue. Yet I'm not sure if I'm still violating some of the best practices. In my case I tried to calculate the mean value all elements of the time series AC variable exported by lsl2ac, e.g. SimpleStream and create a new AC variable. For this I use the following function:

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void example6_t::calculate_mean_value() {
	// Index for going through data chunk
	unsigned int fr;
	// Get EEG/LSL data
    store_ac_single = MHA_AC::get_var_waveform(ac,lsl_time_series.data);
    // Set mean value to 0
    mean_value = 0.0;
    // Sum up all the values of time series
    for(fr = 0; fr < store_ac_single.num_frames*store_ac_single.num_channels; fr++){
        mean_value += store_ac_single.buf[fr];
    }
    // Normalize by divding by number of elements
    mean_value = mean_value/(store_ac_single.num_frames*store_ac_single.num_channels);
    // Insert mean value as new AC variable
    ac.insert_var_float( ac.handle, "Mean_value", &mean_value );
}

This function is executed in the prepare as well as in the process function. Should I only execute parts of the function, meaning only:

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store_ac_single = MHA_AC::get_var_waveform(ac,lsl_time_series.data);
ac.insert_var_float( ac.handle, "Mean_value", &mean_value );

?

What exactly is meant with "memory used for storing AC variable values is allocated and owned by the publishing
plugin and needs to remain valid until the next call to process() or release() of the
same plugin."?

I will attach my code and the configs.

Posted: **Fri Sep 10, 2021 3:41 pm**

Looking only at the code snippets in the forum post: look fine to me.

The open Master Hearing Aid Forum

Proper way to receive an AC variable from a plugin in a chain (especially lsl2ac)?

Proper way to receive an AC variable from a plugin in a chain (especially lsl2ac)?

Re: Proper way to receive an AC variable from a plugin in a chain (especially lsl2ac)?

Re: Proper way to receive an AC variable from a plugin in a chain (especially lsl2ac)?

Re: Proper way to receive an AC variable from a plugin in a chain (especially lsl2ac)?

Re: Proper way to receive an AC variable from a plugin in a chain (especially lsl2ac)?