Instantiation of SingleChannel() with filter_taps leads to errors.

[Qaslo]

An error occurs in version 0.3.3 of quam when instantiating a SingleChannel() with filter_fir_taps or filter_iir_taps defined, adding this channel to a machine object and then calling machine.generate_config().

Example:

from quam.components import *

machine = BasicQuAM()
machine.channels['z'] = SingleChannel(opx_output=('con1', 1), filter_fir_taps=[1.53,-1.529], filter_iir_taps=[0.999,-0.999])
machine.generate_config()

This generates the error:

AttributeError: Cannot overwrite parent attribute of QuamList. To modify QuamList.parent, first set QuamList.parent = None

Can we come up with a fix for this error?

[Qaslo]

A brief look into the source code shows where this error is coming from.

When instantiating SingleChannel, the filter_fir_taps and filter_iir_taps are converted into QuamList objects and assigned a parent attribute taking the value of the SingleChannel object.

However, when calling machine.generate_config(), the method apply_to_config in SingleChannel is called. This reassigns filter_fir_taps and filter_iir_taps to other QuamComponent objects, such as OPXPlusAnalogOutputPort or LFFEMAnalogOutputPort:

# quam/components/channels.py, lines 523 - 538

elif len(self.opx_output) == 2:
    opx_port = OPXPlusAnalogOutputPort(
        *self.opx_output,
        offset=self.opx_output_offset,
        feedforward_filter=self.filter_fir_taps,
        feedback_filter=self.filter_iir_taps,
    )
    opx_port.apply_to_config(config)
else:
    opx_port = LFFEMAnalogOutputPort(
        *self.opx_output,
        offset=self.opx_output_offset,
        feedforward_filter=self.filter_fir_taps,
        feedback_filter=self.filter_iir_taps,
    )
    opx_port.apply_to_config(config)

Assigning filter_fir_taps and filter_iir_taps to another QuamComonent will call the following code:

# quam/core/quam_classes.py, lines 673 - 678

def __setattr__(self, name, value):
    converted_val = convert_dict_and_list(value, cls_or_obj=self, attr=name)
    super().__setattr__(name, converted_val)

    if isinstance(converted_val, QuamBase) and name != "parent":
        converted_val.parent = self

Since filter_fir_taps and filter_iir_taps already have a parent defined, trying to overwrite this in the final line of the above code will lead to an error, since overwriting the parent of a QuamBase object is not allowed.

[Qaslo]

I've implemented a simple fix for the above issue. We need to "unhook" the filter_fir_taps and filter_iir_taps objects from their parents before assigning them to other QuamComponent objects.

Concretely, inserting these lines of code solves the problem:

for filter_tap in [self.filter_fir_taps, self.filter_iir_taps]:
            if isinstance(filter_tap, QuamBase):
                filter_tap.parent = None

The full code for the apply_to_config method in SingleChannel now looks like this:

def apply_to_config(self, config: dict):
        """Adds this SingleChannel to the QUA configuration.

        See [`QuamComponent.apply_to_config`][quam.core.quam_classes.QuamComponent.apply_to_config]
        for details.
        """
        # Add pulses & waveforms
        super().apply_to_config(config)

        if str_ref.is_reference(self.name):
            raise AttributeError(
                f"Channel {self.get_reference()} cannot be added to the config because"
                " it doesn't have a name. Either set channel.id to a string or"
                " integer, or channel should be an attribute of another QuAM component"
                " with a name."
            )

        element_config = config["elements"][self.name]

        if self.intermediate_frequency is not None:
            element_config["intermediate_frequency"] = self.intermediate_frequency

        for filter_tap in [self.filter_fir_taps, self.filter_iir_taps]:
            if isinstance(filter_tap, QuamBase):
                filter_tap.parent = None

        if isinstance(self.opx_output, LFAnalogOutputPort):
            opx_port = self.opx_output
        elif len(self.opx_output) == 2:
            opx_port = OPXPlusAnalogOutputPort(
                *self.opx_output,
                offset=self.opx_output_offset,
                feedforward_filter=self.filter_fir_taps,
                feedback_filter=self.filter_iir_taps,
            )
            opx_port.apply_to_config(config)
        else:
            opx_port = LFFEMAnalogOutputPort(
                *self.opx_output,
                offset=self.opx_output_offset,
                feedforward_filter=self.filter_fir_taps,
                feedback_filter=self.filter_iir_taps,
            )
            opx_port.apply_to_config(config)

        element_config["singleInput"] = {"port": opx_port.port_tuple}

For this, we need to import QuamBase at the top of the file quam/components/channels.py.

from quam.core import QuamBase, QuamComponent, quam_dataclass

Note that a workaround to not running into this issue is to simply pass the values for filter_fir_taps and filter_iir_taps as tuple(float) instead of list(float). This is because tuple objects are not converted to instances of QuamBase and are not assigned a parent, avoiding this issue completely.

Another way to avoid this issue is to instantiate the SingleChannel through an explicit instantiation of OPXPlusAnalogOutputPort. The above example would then be:

from quam.components import *

machine = BasicQuAM()
machine.channels['z'] = SingleChannel(opx_output=
    OPXPlusAnalogOutputPort(*('con1', 1), feedforward_filter=[1.53,-1.529], feedback_filter=[0.999,-0.999])
)
machine.generate_config()

@nulinspiratie I don't have access to publish a branch and create a pull request right now. But since it's only a few lines of code, feel free to simply add the code in this comment - should be straightforward!

[Qaslo]

Another brief comment: Filters also cause an error when calling qmm.open_qm(config) on the config currently generated by quam. The reason for this is the way filters are added to the config in apply_to_config.

In the current version (0.3.3), a channel in config has the following structure:

10: {'delay': 0,
     'shareable': False,
     'crosstalk': {1: 0.0},
     'feedforward_filter': [1.531099692360263, -1.529451467250909], 
     'feedback_filter': [0.999, -0.999],
     'offset': 0.0},

But in version 1.2.0 of the qua documentation, filters should be assigned to channels in the following way.

10: {'delay': 0,
     'shareable': False,
     'crosstalk': {1: 0.0},
     'filter': {'feedforward': [1.531099692360263, -1.529451467250909], 'feedback': [0.999, -0.999]},
     'offset': 0.0},

This bug can be fixed by changing the get_port_properties method in the LFAnalogOutputPort class to the following code:

# quam/components/ports, lines 16-43

@quam_dataclass
class LFAnalogOutputPort(BasePort, ABC):
    fem_type: ClassVar[str] = "LF"
    port_type: ClassVar[str] = "analog_output"

    offset: Optional[float] = None
    delay: int = 0
    crosstalk: Optional[Dict[int, float]] = None
    feedforward_filter: Optional[List[float]] = None
    feedback_filter: Optional[List[float]] = None
    shareable: bool = False

    def get_port_properties(self):
        port_properties = {
            "delay": self.delay,
            "shareable": self.shareable
        }
        if self.crosstalk is not None:
            port_properties["crosstalk"] = self.crosstalk
        if self.feedforward_filter is not None or self.feedback_filter is not None:
            port_properties["filter"] = {}
            if self.feedforward_filter is not None:
                port_properties["filter"]["feedforward"] = list(self.feedforward_filter)
            if self.feedback_filter is not None:
                port_properties["filter"]["feedback"] = list(self.feedback_filter)
        if self.offset is not None:
            port_properties["offset"] = self.offset
        return port_properties

[nulinspiratie]

Hey @Qaslo nice catch, and thanks for the detailed explanation!

I'll be back from holiday in a week, is this blocking you from continuing or can it be fixed once I'm back?

[Qaslo]

No rush @nulinspiratie! I implemented the fixes locally, and they work for me!