spcm 1.2.0

Package for Spectrum Instrumentation GmbH cards

spcm

A high-level, object-oriented Python package for interfacing with Spectrum Instrumentation GmbH devices.

spcm can handle individual cards (Card), StarHubs (Sync), groups of cards (CardStack) and Netboxes (Netbox).

Supported devices

See the SUPPORTED_DEVICES.md file for a list of supported devices.

Requirements

spcm requires the Spectrum Instrumentation driver which is available for Windows and Linux. Please have a look in the manual of your product for more information about installing the driver on the different plattforms.

Installation and dependencies

Start by installing Python 3.9 or higher. We recommend using the latest version. You can download Python from https://www.python.org/.

You would probably also like to install and use a virtual environment, although it's not strictly necessary. See the examples README.md for a more detailed explanation on how to use spcm in a virtual environment.

To install the latest release using pip:

$ pip install spcm

Note that: this will automatically install all the dependencies.

Documentation

The API documentation for the latest stable release is available for reading on GitHub pages.

Please also see the hardware user manual for your specific card for more information about the available functionality.

Using spcm

The spcm package is a high-level object-oriented programming library for controlling Spectrum Instrumentation devices.

Examples

For detailed examples see the src\examples directory. There are several sub-directories each corresponding to a certain kind of functionality. You can find the most recent examples on GitHub.

Hardware interfaces

spcm provides the following classes for interfacing with the different devices.

Name	Description
Card	a class to control the low-level API of Spectrum Instrumentation cards.
Sync	a class for controling StarHub devices.
CardStack	a class that handles the opening and closing of a combination of different cards either with or without a StarHub that synchronizes the cards.
Netbox	a class that handles the opening and closing of the cards in a Netbox

Connect to a device

Opening and closing of cards is handled using the python with statement. This creates a context manager that safely handles opening and closing of a card or a group of cards.

Using device identifiers

Connect to local cards:

import spcm

with spcm.Card('/dev/spcm0') as card:

    # (add your code here)

Connect to remote cards (you can find a card's IP using the Spectrum Control Center software):

import spcm

with spcm.Card('TCPIP::192.168.1.10::inst0::INSTR') as card:
    
    # (add your code here)

Connect to a group of cards synchronized using a StarHub:

import spcm

card_identifiers = ["/dev/spcm0", "/dev/spcm1"]
sync_identifier  = "sync0"

with spcm.CardStack(card_identifiers=card_identifiers, sync_identifier=sync_identifier) as stack:

    # (add your code here)

The CardStack object contains a list of Card objects in the stack.cards parameter and a Sync object in the parameter stack.sync.

Using card type or serial number

Apart from connecting to a device directly through a device identifier it's also possible to connect to local devices using the card type or serial number.

To find the first card of type analog out (SPCM_TYPE_AO) you can do the following:

import spcm

with spcm.Card(card_type=spcm.SPCM_TYPE_AO) as card:
    
    # (add your code here)

See the register SPC_FNCTYPE in the reference manual of your specific device for the kind of card you're using.

If you want to connect to a device based on it's serial number, do the following:

import spcm

with spcm.Card(serial_number=[your serial number here]) as card:
    
    # (add your code here)

See the register SPC_PCISERIALNO in the reference manual of your specific device for more information.

If the device_identifier is given, that card is opened, if at the same time card_type or serial_number are given, then these behave as an additional check too see if the opened card is of a certain type or has that specific serial number.

Demo devices

To test the Spectrum Instrumentation API with user code without hardware, the Control Center gives the user the option to create demo devices. These demo devices can be used in the same manner as real devices. Simply change the device identifier string to the string as shown in the Control Center.

Units and quantities

spcm uses pint to handle all quantities that have a physical unit. To enable the use of quantities simply import the units module from spcm:

from spcm import units

This imports the units object from spcm. This is a UnitRegistry object from pint. Defining a quantity is as simple as:

from spcm import units

frequency = 100 * units.MHz
amplitude = 1 * units.V
# etc...

All methods within the spcm that expect a value related to a physical quantity, support these quantities, for example setting a timeout:

card.timeout(5 * units.s)

See our dedicated examples for more information about where units can be used.

Card Functionality

After opening a card, StarHub, group of cards or Netbox, specific functionality of the cards can be accessed through CardFunctionality classes.

Name	Description
Channels	class for setting up the in- or output stage of the channels of a card
Clock	class for setting up the clock engine of the card
Trigger	class for setting up the trigger engine of the card
MultiPurposeIOs	class for setting up the multi purpose i/o of the card
DataTransfer	class for handling data transfer functionality
Multi	class for handling multiple recording and replay mode functionality
Sequence	class for handling sequence mode functionality
TimeStamp	class for handling time stamped data
Boxcar	class for handling boxcar averaging
BlockAverage	class for handling block averaging functionality
PulseGenerators	class for setting up the pulse generator functionality
DDS	class for handling DDS functionality
DDSCommandList	class for abstracting streaming DDS commands using blocks of commands
DDSCommandQueue	class for abstracting streaming DDS commands using a queue of commands

To use a specific functionality simply initiate an instance of one of the classes and pass a device object:

import spcm

with spcm.Card('/dev/spcm0') as card:

    clock = spcm.Clock(card)
    # (or)
    trigger = spcm.Trigger(card)
    # (or)
    multi_io = spcm.MultiPurposeIOs(card)
    # (or)
    data_transfer = spcm.DataTransfer(card)
    # etc ...

Each of these functionalities typically corresponds to a chapter in your device manual, so for further reference please have a look in the device manual.

Setting up Channels

The Channels functionality allows the user to setup individual channels on a Card or a CardStack. The channels object is also a Python iterator, hence if a channels object is used it a for-loop, each iteration provides a Channel object:

channels = spcm.Channels(card, card_enable=spcm.CHANNEL0 | CHANNEL1)
for channel in channels:
    # do something with each channel

In addition, the user can define the output load connected to the channel (standard value 50 Ohm), to any resistor value or high impedance (units.highZ). With this output load, the amplitude setting is done with repect to this output load:

channels = Channels(card, card_enable=spcm.CHANNEL0 | CHANNEL1)
channels[0].output_load(units.highZ)
channels[0].amp(1 * units.V)
# or for all channels
channels.output_load(units.highZ)
channels.amp(1 * units.V)

This information allows the user to convert the data coming from DataTransfer, using the convert_data() method. See the section "Setting up a data transfer buffer ..." for more details.

Setting up the Clock engine

The Clock engine is used to generate a clock signal that is used as the source for all timing critical processes on the card.

Sample rate

To get the maximum sample rate of the active card and set the sample rate to the maximum, this is an example using internal PLL clock mode:

clock = spcm.Clock(card)
clock.mode(spcm.SPC_CM_INTPLL)
sample_rate = clock.sample_rate(max=True) 
# (or) 
sample_rate = clock.sample_rate(20 * units.MHz) # for a 20 MHz sample rate (see reference manual for allowed values)
print("Current sample rate: {}".format(sample_rate, return_unit=units.MS/units.s))

Setting up the Trigger engine

External trigger

The Trigger engine can be configured for a multitude of different configurations (see the hardware manual for more information about the specific configurations for your device). Here we've given an example for an external trigger arriving at input port ext0, that is DC-coupled. The card is waiting for positiv edge that excedes 1.5 V:

trigger = spcm.Trigger(card)
trigger.or_mask(spcm.SPC_TMASK_EXT0) # set the ext0 hardware input as trigger source
trigger.ext0_mode(spcm.SPC_TM_POS) # wait for a positive edge
trigger.ext0_level0(1.5 * units.V)
trigger.ext0_coupling(spcm.COUPLING_DC) # set DC coupling

Setting up the multi-purpose I/O lines

See the hardware manual, for the multi-purpose I/O lines functionality that can be programmed.

Setting up a data transfer buffer for recording (digitizer) or replay (AWG)

Recording (Digitizing)

To transfer data to or from the card, we have to setup a data transfer object. This object allocates an amount the memory of the card (memory_size) and a Direct Memory Access (DMA) buffer on the host pc (allocate_buffer). Half of the samples are taken before the trigger, as configured by the trigger engine, and half of the samples are recorded afterwards. Then the transfer from the card to the host pc is started and the program waits until the DMA is filled.

# define the data buffer
num_samples = 4 * units.KiS # 1 KiS = 1 KibiSamples = 1024 Samples
data_transfer = spcm.DataTransfer(card)
data_transfer.memory_size(num_samples)
data_transfer.allocate_buffer(num_samples)
data_transfer.post_trigger(num_samples // 2)
# Start DMA transfer
data_transfer.start_buffer_transfer(spcm.M2CMD_DATA_STARTDMA)

# start card and wait until the memory is filled
card.start(spcm.M2CMD_CARD_ENABLETRIGGER, spcm.M2CMD_DATA_WAITDMA)

# (your code handling the recorded data comes here)

To access the recorded data, the data transfer object holds a NumPy array object data_transfer.buffer that is directly mapped to the DMA buffer. This buffer can be directly accessed by the different analysis methods available in the NumPy package:

import numpy as np

# The extrema of the data
minimum = np.min(data_transfer.buffer, axis=1)
maximum = np.max(data_transfer.buffer, axis=1)

This data can be further processed or plotted using, for example, matplotlib.

Replay (Generation)

The setup of the DMA for replay is very similar. First card memory is allocated with memory_size and then a DMA buffer is allocated (allocated_buffer) and made accessible though the NumPy object data_transfer.buffer, which can then be written to using standard NumPy methods. Finally, data transfer from the host PC to the card is started and the programming is waiting until all the data is transferred:

num_samples = 4 * units.KiS # 1 KiS = 1 KibiSamples = 1024 Samples
data_transfer = spcm.DataTransfer(card)
data_transfer.memory_size(num_samples)
data_transfer.allocate_buffer(num_samples)
data_transfer.loops(0) # loop continuously
# simple linear ramp for analog output cards
num_samples_magnitude = num_samples.to(units.S).magnitude
data_transfer.buffer[:] = np.arange(-num_samples_magnitude//2, num_samples_magnitude//2).astype(np.int16)

data_transfer.start_buffer_transfer(spcm.M2CMD_DATA_STARTDMA, spcm.M2CMD_DATA_WAITDMA)

Data transfer

In the above it's assume that all the data has been transferred from the card into the buffer object, however if you're working in FIFO mode or you've defined the buffer to be smaller then the assigned card memory size, then the card will write to parts of the memory and tell you were it wrote.

This can be either handled manually (see the reference manual of your card, or the methods avail_card_len(), avail_user_pos() and avail_user_len()).

Secondly, it can also be handled with Python iterators functionality. If the data_transfer object is handed to a for-loop, then in each iteration a view of the current active memory part is given in the form of a NumPy array and the user can do calculations on that.

# Get a block of data
for data_block in data_transfer:
    # data_block is a NumPy array view of the currently active buffer part
    for channel in channels:
        data_units = channel.convert_data(data_block[:, channel])
        minimum = np.min(data_units)
        maximum = np.max(data_units)
        print(f"Minimum: {minimum} - maximum: {maximum}")

The same principle also works with generator cards (see the example 2_gen_fifo.py).

Multiple recording / replay

In case of multiple recording / replay, the memory is divided in equally sized segments, that are populated / replayed when a trigger is detected. Multiple triggers each trigger the next segment to be populated or replayed.

The following code snippet shows how to setup the buffer for 4 segments with each 128 Samples:

samples_per_segment = 128 * units.S
num_segments = 4
multiple_recording = spcm.Multi(card)
multiple_recording.memory_size(samples_per_segment*num_segments)
multiple_recording.allocate_buffer(segment_samples=samples_per_segment, num_segments=num_segments)
multiple_recording.post_trigger(samples_per_segment // 2)
multiple_recording.start_buffer_transfer(spcm.M2CMD_DATA_STARTDMA)

Again there are half the samples before and half the samples after the trigger.

Timestamps

See the example 6_acq_fifo_multi_ts_poll.py in the examples folder 1_acquisition for more information about the usage of timestamps. Moreover, detailed information about timestamps can be found in the corresponding chapter in the specific hardware manual.

To setup the timestamp buffer:

ts = spcm.TimeStamp(card)
ts.mode(spcm.SPC_TSMODE_STARTRESET, spcm.SPC_TSCNT_INTERNAL)
ts.allocate_buffer(num_time_stamps)

The user can then use polling to acquire time stamp data from the card.

Additional functionality

Pulse generator

Please see the folder 4_pulse-generator in the examples folder for several dedicated examples. In the following, there is a simple example for setting up a single pulse generator on x0.

Create a pulse generators object and get the clock rate used by the pulse generator. Use that to calculate the period of a 1 MHz signal and the half of that period we'll have a high signal (hence 50% duty cycle). The pulse generator will start if the trigger condition is met without delay and loops infinitely many times. The triggering condition is set to the card software trigger. See more details in the pulse generator chapter in the specific hardware manual.

pulse_generators = spcm.PulseGenerators(card)

# generate a continuous signal with 1 MHz
pulse_generators[0].pulse_period(1 * units.us)
# pulse_generators[0].repetition_rate(1 * units.MHz) # (or)
pulse_generators[0].duty_cycle(50 * units.percent)
# pulse_generators[0].pulse_length(0.5 * units.us) # (or)
pulse_generators[0].start_delay(0 * units.us)
pulse_generators[0].repetitions(0) # 0: infinite
pulse_generators[0].start_condition_state_signal(spcm.SPCM_PULSEGEN_MUX1_SRC_UNUSED)
pulse_generators[0].start_condition_trigger_signal(spcm.SPCM_PULSEGEN_MUX2_SRC_SOFTWARE)
pulse_generators[0].invert_start_condition(False)

# and write the pulse generator settings
pulse_generators.write_setup()

# start all pulse generators that wait for a software command
pulse_generators.force()

This will start the pulse generator to continuously output a 1 MHz signal.

Sequence replay mode (AWG only)

Please see the example 3_gen_sequence.py in the folder 2_generation of the examples to see an example dedicated to the Sequence replay mode.

DDS (AWG only)

Please see the examples in the dedicated examples folder 3_dds for all the functionality provided by the DDS framework. Moreover, please also have a look at the corresponding hardware manual.

Boxcar (Digitizer only)

See the corresponding chapter in the hardware manual for more information about boxcar averaging and the registers used.

Block average (Digitizer only)

See the corresponding chapter in the hardware manual for more information about block averaging and the registers used.

Acknowledgements

We would like to thank Christian Baker for fruitful discussions and inspiration on how to setup the spcm package.