Sequencer

This section will explain how the sequencers of the Pulsar QCM and QRM are controlled. Every sequencer is controlled using the same functions and parameters, which either take the sequencer index as a parameter or indicate which sequencer they operate on based on the index in their name.

Note

As of version 0.5.0 of the Pulsar QRM, new functionality has been added to the acquisition path (e.g. real-time demodulation, (weighed) integration, discretization, averaging, binning). More details about this functionality will be added to the documentation as soon as possible. For now, please have a look at the binned acquisition tutorial to get started.

Overview

The sequencers are split into the sequence processor, AWG and acquisition paths as shown in the figures below. Each sequence processor controls one AWG path and, in case of the Pulsar QRM, one acquisition path. The AWG path and acquisition path are discussed in more detail in section Pulsar. Each sequencer processor is, in turn, split into a classical and real-time pipeline. The classical pipeline is responsible for any classical instructions related to program flow or arithmetic and the real-time pipeline is responsible for real-time instructions that are used to create the experiment timeline.

Pulsar QCM sequencer with AWG path.

Pulsar QRM sequencer with AWG and acquisition paths.

The sequencers are started and stopped by calling the arm_sequencer(), start_sequencer() and stop_sequencer() functions. Once started they will execute the sequence described in the next section.

Sequence

The sequencers are programmed with a sequence using the sequencer#_sequence() function parameter. This parameter expects a sequence in the form of a JSON compatible file that contains the waveform, weight, acquistion and program information. The JSON file is expected to adhere to the following format:

• waveforms: Indicates that the following waveforms are intended for the AWG path.

  • waveform name: Replace by string containing the waveform name.

    • data: List of floating point values to express the waveform.

    • index: Integer index used by the Q1ASM program to refer to the waveform.

• weights: Indicates that the following weight functions are intended for the integration units of the acquisition path (only used by the Pulsar QRM).

  • weight name: Replace by string containing the weight name.

    • data: List of floating point values to express the weight.

    • index: Integer index used by the Q1ASM program to refer to the weight.

• acquisitions: Indicates that the following acquisitions are available for the acquisition path to refer to (only used by the Pulsar QRM).

  • acquisition name: Replace by string containing the acquisition name.

    • num_bins: Number of bins in acquisition.

    • index: Integer index used by the Q1ASM program to refer to the acquisition.

• program: Single string containing the entire sequence processor Q1ASM program.

Example of a sequence JSON file.

{
    "waveforms": {
        "gaussian": {
            "data": [
                0.0075756774442599355, 0.5812730178734145, 0.5812730178734145, 0.0075756774442599355
            ],
            "index": 0
        },
        "sine": {
            "data": [0.0, 1.0, 1.2246467991473532e-16, -1.0],
            "index": 1
        }
    },
    "weights": {
        "gaussian": {
            "data": [0.0075756774442599355, 0.5812730178734145, 0.5812730178734145, 0.0075756774442599355],
            "index": 0
        },
        "sine": {
            "data": [0.0, 1.0, 1.2246467991473532e-16, -1.0],
            "index": 1
        }
    },
    "acquisitions": {
        "binned": {
            "num_bins": 100000,
            "index": 0
        },
        "averaged": {
            "num_bins": 1,
            "index": 1
        }
    },
    "program": "\nplay 0,1,4 #Play waveforms and wait 4ns.\nacquire 1,0,16380 #Acquire wait for scope mode acquisition to finish.\nstop #Stop.\n"
}

Program

The sequence programs are written in the custom Q1ASM assembly language described in the following sections. All sequence processor instructions are executed by the classical pipeline and the real-time instructions are also executed by the real-time pipeline. These latter instructions are intended to control the AWG and acquisition paths in a real-time fashion. Once processed by the classical pipeline they are queued in the real-time pipeline awaiting further execution. A total of 32 instructions can be queued and once the queue is full, the classical part will stall on any further real-time instructions.

Once execution of the real-time instructions by the real-time pipeline is started, care must be taken to not cause an underrun of the queue. An underrun will potentially cause undetermined real-time behaviour and desynchronize any synchronized sequencers. Therefore, when this is detected, the sequencer is completely stopped. A likely cause of underruns is a loop with a very short (i.e. < 24ns) real-time run-time, since the jump of a loop takes some cycles to be execute by the classical pipeline.

Finally, be aware that moving data into a register using an instruction takes a cycle to complete. This means that when an instruction reads from a register that the previous instruction has written to, a nop instruction must to be placed in between these consecutively instructions for the value to be correctly read.

The state of the sequencers, including any errors, can be queried through get_sequencer_state().

Instructions

Instructions	Argument 0	Argument 1	Argument 2	Argument 3	Argument 4	Description
Control
illegal	–	–	–	–	–	Instruction that should not be executed. If it is executed, the sequencer will stop with the illegal instruction flag set.
stop	–	–	–	–	–	Instruction that stops the sequencer.
nop	–	–	–	–	–	No operation instruction, that does nothing. It is used to pass a single cycle in the classic part of the sequencer without any operations.
Jumps
jmp	Immediate, Register, Label	–	–	–	–	Jump to the next instruction indicated by argument 0.
jge	Register	Immediate	Immediate, Register, Label	–	–	If argument 0 is greater or equal to argument 1, jump to the instruction indicated by argument 2.
jlt	Register	Immediate	Immediate, Register, Label	–	–	If argument 0 is less than argument 1, jump to the instruction indicated by argument 2.
loop	Register	Immediate, Register, Label	–	–	–	Subtract argument 0 by one and jump to the instruction indicated by argument 1 until argument 0 reaches zero.
Arithmetic
move	Immediate, Register	Register	–	–	–	Argument 0 is moved / copied to argument 1.
not	Immediate, Register	Register	–	–	–	Bit-wise invert argument 0 and move the result to argument 1.
add	Register	Immediate, Register	Register	–	–	Add argument 1 to argument 0 and move the result to argument 2.
sub	Register	Immediate, Register	Register	–	–	Subtract argument 1 from argument 0 and move the result to argument 2.
and	Register	Immediate, Register	Register	–	–	Bit-wise AND argument 0 and argument 1 and move the result to argument 2.
or	Register	Immediate, Register	Register	–	–	Bit-wise OR argument 0 and argument 1 and move the result to argument 2.
xor	Register	Immediate, Register	Register	–	–	Bit-wise XOR argument 0 and argument 1 and move the result to argument 2.
asl	Register	Immediate, Register	Register	–	–	Bit-wise left-shift argument 0 by argument 1 number of bits and move the result to argument 2.
asr	Register	Immediate, Register	Register	–	–	Bit-wise right-shift argument 0 by argument 1 number of bits and move the result to argument 2.
Software request
sw_req	Immediate, Register	–	–	–	–	Generate software request interrupt with argument 0 value being passed as interrupt argument (currently not implemented).
Real-time pipeline instructions
set_mrk	Immediate, Register	–	–	–	–	Set marker output channels to argument 0 (bits 0-3), where the bit index corresponds to the channel index. The set value is OR´ed by that of other sequencers. The parameters are cached and only updated when the upd_param, play, acquire or acquired_weighed instructions are executed.
reset_ph	–	–	–	–	–	Reset the absolute phase of the NCO used by the AWG and acquisition to 0°. This also resets any relative phase offsets that were already statically or dynamically set. The reset is cached and only applied when the upd_param, play, acquire or acquired_weighed instructions are executed.
set_ph	Immediate, Register	Immediate, Register	Immediate, Register	–	–	Set the relative phase of the NCO used by the AWG and acquisition. The phase is divided into a coarse (argument 0), fine (argument 1) and ultra-fine (argument 2) segment. The coarse segment is divided into 400 steps of 0.9°. The fine segment is divided into 400 steps of 2.25e-3°. And the ultra-fine segment is divided into 6250 steps of 3.6e-7°. The parameters are cached and only updated when the upd_param, play, acquire or acquired_weighed instructions are executed. The arguments are either all set through immediates or registers.
set_ph_delta	Immediate, Register	Immediate, Register	Immediate, Register	–	–	Set an offset on top of the relative phase of the NCO used by the AWG and acquisition. The offset is applied on top of the phase set using set_ph. See set_ph for more details regarding the arguments. The parameters are cached and only updated when the upd_param, play, acquire or acquired_weighed instructions are executed.
set_awg_gain	Immediate, Register	Immediate, Register	–	–	–	Set AWG gain for path 0 using argument 0 and path 1 using argument 1. Both gain values are divided in 2**sample path width steps. The parameters are cached and only updated when the upd_param, play, acquire or acquired_weighed instructions are executed. The arguments are either all set through immediates or registers.
set_awg_offs	Immediate, Register	Immediate, Register	–	–	–	Set AWG gain for path 0 using argument 0 and path 1 using argument 1. Both offset values are divided in 2**sample path width steps. The parameters are cached and only updated when the upd_param, play, acquire or acquired_weighed instructions are executed. The arguments are either all set through immediates or registers.
upd_param	Immediate	–	–	–	–	Update the marker, phase, phase offset, gain and offset parameters set using their respective instructions and then wait for argument 0 number of nanoseconds.
play	Immediate, Register	Immediate, Register	Immediate	–	–	Update the marker, phase, phase offset, gain and offset parameters set using their respective instructions, start playing AWG waveforms stored at indexes argument 0 on path 0 and argument 1 on path 1 and finally wait for argument 2 number of nanoseconds. The arguments are either all set through immediates or registers.
acquire	Immediate	Immediate, Register	Immediate	–	–	Update the marker, phase, phase offset, gain and offset parameters set using their respective instruction, start the acquisition refered to using index argument 0 and store the bin data in bin index argument 1, finally wait for argument 2 number of nanoseconds. Integration is executed using a square weight with a preset length through the associated QCoDeS parameter. The arguments are either all set through immediates or registers.
acquire_weighed	Immediate	Immediate, Register	Immediate, Register	Immediate, Register	Immediate	Update the marker, phase, phase offset, gain and offset parameters set using their respective instruction, start the acquisition refered to using index argument 0 and store the bin data in bin index argument 1, finally wait for argument 4 number of nanoseconds. Integration is executed using weights stored at indexes argument 2 for path 0 and argument 3 for path 1. The arguments are either all set through immediates or registers.
wait	Immediate, Register	–	–	–	–	Wait for argument 0 number of nanoseconds.
wait_trigger	Immediate, Register	–	–	–	–	Wait for external trigger and then wait for argument 0 number of nanoseconds.
wait_sync	Immediate, Register	–	–	–	–	Wait for SYNQ to complete on all connected sequencers over all connected instruments and then wait for argument 0 number of nanoseconds.

Note

The duration argument for upd_param, play, acquire, acquire_weighed, wait, wait_trigger and wait_sync needs to a be multiple of 4ns. This will be reduced to 1ns in the future.

Arguments

Arguments	Format	Description
Immediate	#	32-bit decimal value (e.g. 1000)
Register	R#	Register address in range 0 to 63 (e.g. R0) pointing to a 32-bit unsigned integer
Label	@label	Label name string (e.g. @main)

Labels

Any instruction can be preceded by a label. This label can be used as a reference to that specific instruction. In other words, it can be used as a goto-point by any instruction that can alter program flow (i.e. jmp, jge, jlt and loop). The label must be followed by a ‘:’ character and a whitespace before the actual referenced instruction.

Example

This is a simple example of a Q1ASM program. It enables each marker channel output for 1μs and then stops.

      move      1,R0        # Start at marker output channel 0 (move 1 into R0)
      nop                   # Wait a cycle for R0 to be available.

loop: set_mrk   R0          # Set marker output channels to R0
      upd_param 1000        # Update marker output channels and wait 1μs.
      asl       R0,1,R0     # Move to next marker output channel (left-shift R0).
      nop                   # Wait a cycle for R0 to be available.
      jlt       R0,16,@loop # Loop until all 4 marker output channels have been set once.

      set_mrk   0           # Reset marker output channels.
      upd_param 4           # Update marker output channels.
      stop                  # Stop sequencer.

Waveforms

The waveforms are expressed as a list of floating point values in the range of 1.0 to -1.0 with a resolution of one nanosecond per sample. The AWG path uses these waveforms to parametrically generate pulses on its outputs.

Waveform playback is started by the play instructions. Each waveform is paired with an index, which is used by this instruction to refer to the associated waveform. The waveform is then completely played irrespective of further sequence processor instructions, except when the sequence processor issues the playback of another waveform, in which case the waveform will be stopped and the new waveform will start. When waveforms are not played back-to-back, the intermediate time will be filled by samples with a value of zero.

The programmed waveforms can be retrieved using get_waveforms().

Weights

The weights are expressed as a list of floating point values in the range of 1.0 to -1.0 with a resolution of one nanosecond per sample. The integration units in the acquisition path apply (i.e. multiply) these weights during the integration process when the acquisition path is triggered for weighed integration.

Weighed integration is triggered by the acquire_weighed instruction. Each weight is paired with an index, which is used by this instruction to refer to the associated weight. The weight is then played, like the waveforms discussed in the previous section and determines the length of the integration. The weighed integration process continues irrespective of further sequence processor instructions, except when the sequence processor issues another acquisition using the acquire or acquire_weighed instructions, in which case the integration will be stopped, the result will be stored and a new integration will start.

The programmed weights can be retrieved using get_weights().

Acquisitions

Acquisitions are started by the acquire or acquire_weighed instructions and will trigger the capture of 16k input samples on both inputs. This mode of operation is called scope mode and will store the raw input samples in a temporary buffer. Every time an acquisition is started, this temporary memory is overwritten, so it is vital to move the samples from the temporary buffer to a more lasting location before the start of the next acquisition. This is be done by calling store_scope_acquisition(), which moves the samples into the specified acquisition in the acquisition list of the sequencer, located in the RAM of the instrument. Multiple acquisitions can be stored in this list before being retrieved from the instrument by simply calling get_acquisitions(). Acquisitions are returned as a dictionary of acquisitions. Scope mode data is located under the scope key as lists of floating point values in a range of 1.0 to -1.0 with a resolution of one nanosecond per sample, as well as an indication if the ADC was out-of-range during the measurement.

Note

Before calling store_scope_acquisition(), be sure to call get_sequencer_state() and get_acquisition_state() in that order. This ensures that both the sequencer has finished and that there is an acquisition ready.

The acquisition path also has an averaging function set through the scope_acq_avg_mode_en_path#() parameters. This enables the automatic accumulation of acquisitions, where sample N of acquisition M is automatically accumulated to sample N of acquisition M+1. This happens while the acquisition is still in the temporary buffer, so after the desired number of averaging acquisitions is completed, call store_scope_acquisition() to store the accumulated result in the acquisition list. Once retrieved from the instrument, the accumulated samples will automatically be divided by the number of averages to get the actual averaged acquisition result.

Tip

For debug purposes, the acquisition path can also be triggered using a trigger level, where if the input exceeds this level, an acquisition is started. See the sequencer#_trigger_mode_acq_path#() and sequencer#_trigger_level_acq_path#() parameters for more information.

Continuous waveform mode

The sequencer also supports a continuous waveform mode of operation, where the waveform playback control of sequence processor is completely bypassed and a single waveform is just played back on a loop. This mode can be enabled using the sequencer#_cont_mode_en_awg_path#() parameter and the waveform can be selected using the sequencer#_cont_mode_waveform_idx_awg_path#() parameter. The waveforms used in this mode must be a multiple of four samples long (i.e. 4ns).

When in continuous mode, simply program, arm, start and stop the sequencer using the regular control functions and parameters (i.e. sequencer#_sequence(), arm_sequencer(), start_sequencer() and stop_sequencer()). However, be aware that the sequencer processor can still control parts of the AWG path, like phase, gain and offset, while the sequencer operates in this mode. Therefore, we advise to program the sequence processor with a single stop instruction.

Note

We realise that the current way of controlling this mode is not optimal, so in the near future we will be implementing additional driver support to streamline this mode.