larpix-control

Control the LArPix chip

Setup and installation

This code is intended to work on Python 3.9+.

Install larpix-control from pip with

pip install larpix-control

To return your namespace to the pre-larpix state, just run pip uninstall larpix-control. If you'd prefer to download the code yourself, you can. Just run pip install . from the root directory of the repository.

Tests

You can run tests to convince yourself that the software works as expected. After pip installing this package, you can run the tests from the repository root directory with the simple command pytest.

You can read the tests to see examples of how to call all of the common functions.

File structure

The larpix package contains:

larpix
├── controller.py
├── timestamp.py
├── key.py
├── chip.py
├── quickstart.py
├── bitarrayhelper.py
├── packet
│   ├── packet_v2.py
│   ├── packet_v1.py
│   ├── packet_collection.py
│   ├── sync_packet.py
│   ├── trigger_packet.py
│   ├── message_packet.py
│   ├── timestamp_packet.py
│   └── __init__.py
├── io
│   ├── pacman_io.py
│   ├── serialport.py
│   ├── multizmq_io.py
│   ├── fakeio.py
│   ├── zmq_io.py
│   ├── io.py
│   └── __init__.py
├── __init__.py
├── configuration
│   ├── configuration_v2.py
│   ├── configuration_v1.py
│   ├── configuration.py
│   ├── configuration_lightpix_v1.py
│   └── __init__.py
├── format
│   ├── hdf5format.py
│   ├── pacman_msg_format.py
│   ├── message_format.py
│   └── __init__.py
├── logger
│   ├── h5_logger.py
│   ├── logger.py
│   ├── stdout_logger.py
│   └── __init__.py
├── configs
│   ├── __init__.py
│   ├── controller
│   │   ├── __init__.py
│   │   ├── network-3x3-tile-channel0.json
│   │   ├── network-3x3-tile-channel2.json
│   │   ├── network-3x3-tile-channel1.json
│   │   ├── lightpix_v1_example.json
│   │   ├── v2_example.json
│   │   ├── bare-die-v2-v1.0.0.json
│   │   ├── pcb-10_chip_info.json
│   │   ├── pcb-1_chip_info.json
│   │   ├── pcb-2_chip_info.json
│   │   ├── pcb-3_chip_info.json
│   │   ├── pcb-4_chip_info.json
│   │   ├── pcb-5_chip_info.json
│   │   └── pcb-6_chip_info.json
│   ├── io
│   │   ├── __init__.py
│   │   ├── default.json
│   │   ├── daq-srv1.json
│   │   ├── daq-srv2.json
│   │   ├── daq-srv3.json
│   │   ├── daq-srv4.json
│   │   ├── daq-srv5.json
│   │   ├── daq-srv6.json
│   │   ├── daq-srv7.json
│   │   ├── pacman.json
│   │   ├── pacman_loopback.json
│   │   └── loopback.json
│   └── chip
│       ├── __init__.py
│       ├── default_v2.json
│       ├── csa_bypass.json
│       ├── quiet.json
│       ├── default.json
│       ├── physics.json
│       └── default_lightpix_v1.json
├── serial_helpers
│   ├── analyzers.py
│   ├── dataformatter.py
│   ├── dataloader.py
│   ├── datalogger.py
│   └── __init__.py
└── larpix.py

scripts/
├── gen_controller_config.py
└── gen_hydra_simple.py

Minimal working example

So you're not a tutorials kind of person. Here's a minimal working example for you to play around with:

>>> from larpix import Controller, Packet_v2
>>> from larpix.io import FakeIO
>>> from larpix.logger import StdoutLogger
>>> controller = Controller()
>>> controller.io = FakeIO()
>>> controller.logger = StdoutLogger(buffer_length=0)
>>> controller.logger.enable()
>>> chip1 = controller.add_chip('1-1-2', version=2)  # (access key)
>>> chip1.config.threshold_global = 25
>>> controller.write_configuration('1-1-2', chip1.config.register_map['threshold_global']) # chip key, register 64
[ Key: 1-1-2 | Chip: 2 | Upstream | Write | Register: 64 | Value: 25 | Parity: 1 (valid: True) ]
Record: [ Key: 1-1-2 | Chip: 2 | Upstream | Write | Register: 64 | Value: 25 | Parity: 1 (valid: True) ]
>>> packet = Packet_v2(b'\x02\x91\x15\xcd[\x07\x85\x00')
>>> packet_bytes = packet.bytes()
>>> pretend_input = ([packet], packet_bytes)
>>> controller.io.queue.append(pretend_input)
>>> controller.run(0.05, 'test run')
Record: [ Key: None | Chip: 2 | Downstream | Data | Channel: 5 | Timestamp: 123456789 | First packet: 0 | Dataword: 145 | Trigger: normal | Local FIFO ok | Shared FIFO ok | Parity: 0 (valid: True) ]
>>> print(controller.reads[0])
[ Key: None | Chip: 2 | Downstream | Data | Channel: 5 | Timstamp: 123456789 | Dataword: 145 | Trigger: normal | Local FIFO ok | Shared FIFO ok | Parity: 0 (valid: True) ]

Tutorial

This tutorial runs through how to use all of the main functionality of larpix-control.

To access the package contents, use one of the two following import statements:

import larpix  # use the larpix namespace
# or ...
from larpix import *  # import all core larpix classes into the current namespace

The rest of the tutorial will assume you've imported all of the core larpix classes via a from larpix import * command.

Create a LArPix Controller

The LArPix Controller translates high-level ideas like "read configuration register 10" into communications to and from LArPix ASICs, and interprets the received data into a usable format.

Controller objects communicate with LArPix ASICs via an IO interface. Currently available IO interfaces are SerialPort, ZMQ_IO and FakeIO. We'll work with FakeIO in this tutorial, but all the code will still work with properly initialized versions of the other IO interfaces.

Set things up with

from larpix.io import FakeIO
from larpix.logger import StdoutLogger
controller = Controller()
controller.io = FakeIO()
controller.logger = StdoutLogger(buffer_length=0)
controller.logger.enable()

The FakeIO object imitates a real IO interface for testing purposes. It directs its output to stdout (i.e. it prints the output), and it takes its input from a manually-updated queue. At the end of each relevant section of the tutorial will be code for adding the expected output to the queue. You'll have to refill the queue each time you run the code.

Similarly, the StdoutLogger mimics the real logger interface for testing. It prints nicely formatted records of read / write commands to stdout every buffer_length packets. The logger interface requires enabling the logger before messages will be stored. Before ending the python session, every logger should be disabled to flush any remaining packets stored in the buffer.

Set up LArPix Chips

Chip objects represent actual LArPix ASICs. For each ASIC you want to communicate with, create a LArPix Chip object and add it to the Controller.

chipid = 5
chip_key = '1-1-5'
chip5 = controller.add_chip(chip_key, version=2)

chip5 = controller[chip_key] # get chip object
chip5 = controller[1,1,5] # gets same chip object

The chip_key field specifies the necessary information for the controller.io object to route packets to/from the chip. The details of how this key maps to a physical chip is implemented separately for each larpix.io class.

The key itself consists of 3 1-byte integer values that represent the 3 low-level layers in larpix readout:

• the io group: this is the highest layer and represents a control system that communicates with multiple IO channels

• the io channel: this is the middle layer and represents a single MOSI/MISO pair

• the chip id: this is the lowest layer and represents a single chip on a MOSI/MISO network

If you want to interact with chip keys directly, you can instantiate one using a valid keystring (three 1-byte integers separated by dashes, e.g. '1-1-2'). Please note that the ids of 0, 1, and 255 are reserved for special functions.

from larpix import Key
example_key = Key(1,2,3)

You can grab relevant information from the key via a number of useful methods and attributes:

example_key.io_group  # 1
example_key.io_channel  # 2
example_key.chip_id  # 3
example_key.to_dict() # returns a dict with the above keys / values

If you are using a Key in a script, we recommend that you generate the keys via the Key(<io_group>,<io_channel>,<chip_id>) method which will protect against updates to the keystring formatting.

You can read the docs to learn more about Key functionality.

Set up LArPix Hydra network

The controller object contains an internal structure representing the Hydra networks on each of the io channels. This structure can be accessed via controller.network and modified using the controller.add_network_node and controller.add_network_link methods. However, it can be a tedious and error-prone process to add each link to the network representation. So, there exists a friendlier configuration file that is used to generate these network links.

To load a network configuration into the controller:

controller.load('controller/v2_example.json')
print(controller.chips) # chips that have been loaded into controller
list(controller.network[1][1]['miso_ds'].edges) # all links contained in the miso_ds graph
list(controller.network[1][1]['miso_us'].nodes) # all nodes within the miso_us graph
list(controller.network[1][1]['mosi'].edges) # all links within the mosi graph

Each graph is represented by a networkx directed graph and can be examined and queried in that way. All edges point in the direction of data flow.

list(controller.network[1][1]['mosi'].in_edges(2)) # all links pointing to chip 2 in mosi graph
list(controller.network[1][1]['miso_ds'].successors(3)) # all chips receiving downstream data packets from chip 3
controller.network[1][1]['mosi'].edges[(3,2)]['uart'] # check the physical uart channel that chip 2 listens to chip 3 via
controller.network[1][1]['mosi'].nodes[2]['root'] # check if designated root chip

After loading the network into the controller, the init_network command automates the process of bringing up individual chips in the network.

controller.init_network(1,1) # issues packets required to initialize the 1,1 hydra network
print(controller['1-1-2'].config.chip_id)
print(controller['1-1-3'].config.enable_miso_downstream)

This issues configuration commands in the proper order so that upstream chips are configured before downstream chips. If you'd like to reset the network configuration

controller.reset_network(1,1)

can be used to reverse the configuration commands issued with init_network. These processes are not "smart" in that they blindly issue config commands assuming the network is either fully configured or in a default state, so buyer beware.

The network initialization can be broken down into single steps by also passing along the chip id:

controller.init_network(1,1,2) # configures only chip 2
controller.init_network(1,1,3) # configures only chip 3

But this requires initializing the chips in the proper order. You can get the chip keys in order of their depth within the network via

controller.get_network_keys(1,1) # gets a list of chip keys starting at the root node and descending
controller.get_network_keys(1,1,root_first_traversal=False) # get list of chip keys starting at deepest chips and ascending

Adjust the configuration of the LArPix Chips

Each Chip object manages its own configuration in software. Configurations can be adjusted by name using attributes of the Chip's configuration:

chip5.config.threshold_global = 35  # entire register = 1 number
chip5.config.enable_periodic_reset = 1  # one bit as part of a register
chip5.config.channel_mask[20] = 1  # one bit per channel

Values are validated, and invalid values will raise exceptions.

Note: Changing the configuration of a Chip object does not change the configuration on the ASIC.

Once the configuration is set, the new values must be sent to the LArPix ASICs. There is an appropriate Controller method for that:

controller.write_configuration(chip_key)  # send all registers
controller.write_configuration(chip_key, 32)  # send only register 32
controller.write_configuration(chip_key, [32, 50])  # send registers 32 and 50
controller.write_configuration(chip_key, 'threshold_global') # send register for 'threshold_global'

Register addresses can be looked up using the configuration object:

threshold_global_reg = chip5.config.register_map['threshold_global']

And register names:

threshold_global_name = chip5.config.register_map_inv[64]

For configurations which extend over multiple registers, the relevant attribute will end in _addresses. Certain configurations share a single register, whose attribute has all of the names in it. View the documentation or source code to find the name to look up. (Or look at the LArPix data sheet.)

Reading the configuration from LArPix ASICs

The current configuration state of the LArPix ASICs can be requested by sending out "configuration read" requests using the Controller:

controller.read_configuration(chip_key)

The same variations to read only certain registers are implemented for reading as for writing.

The responses from the LArPix ASICs are stored for inspection. See the section on "Inspecting received data" for more.

FakeIO queue code:

packets = chip5.get_configuration_read_packets()
bytestream = b'bytes for the config read packets'
controller.io.queue.append((packets, bytestream))

Receiving data from LArPix ASICs

When it is first initialized, the LArPix Controller ignores and discards all data that it receives from LArPix. The Controller must be activated by calling start_listening(). All received data will then be accumulated in an implementation-dependent queue or buffer, depending on the IO interface used. To read the data from the buffer, call the controller's read() method, which returns both the raw bytestream received as well as a list of LArPix Packet objects which have been extracted from the bytestream. To stop listening for new data, call stop_listening(). Finally, to store the data in the controller object, call the store_packets method. All together:

controller.start_listening()
# Data arrives...
packets, bytestream = controller.read()
# More data arrives...
packets2, bytestream2 = controller.read()
controller.stop_listening()
message = 'First data arrived!'
message2 = 'More data arrived!'
controller.store_packets(packets, bytestream, message)
controller.store_packets(packets, bytestream2, message2)

There is a common pattern for reading data, namely to start listening, then check in periodically for new data, and then after a certain amount of time has passed, stop listening and store all the data as one collection. The method run(timelimit, message) accomplishes just this.

duration = 10  # seconds
message = '10-second data run'
controller.run(duration, message)

FakeIO queue code for the first code block:

packets = [Packet_v2()] * 40
bytestream = b'bytes from the first set of packets'
controller.io.queue.append((packets, bytestream))
packets2 = [Packet_v2()] * 30
bytestream2 = b'bytes from the second set of packets'
controller.io.queue.append((packets2, bytestream2))

fakeIO queue code for the second code block:

packets = [Packet_v2()] * 5
bytestream = b'[bytes from read #%d] '
for i in range(100):
    controller.io.queue.append((packets, bytestream%i))

Inspecting received data

Once data is stored in the controller, it is available in the reads attribute as a list of all data runs. Each element of the list is a PacketCollection object, which functions like a list of Packet objects each representing one LArPix packet.

PacketCollection objects can be indexed like a list:

run1 = controller.reads[0]
first_packet = run1[0]  # Packet object
first_ten_packets = run1[0:10]  # smaller PacketCollection object

first_packet_bits = run1[0, 'bits']  # string representation of bits in packet
first_ten_packet_bits = run1[0:10, 'bits']  # list of strings

PacketCollections can be printed to display the contents of the Packets they contain. To prevent endless scrolling, only the first ten and last ten packets are displayed, and the number of omitted packets is noted. To view the omitted packets, use a slice around the area of interest.

print(run1)  # prints the contents of the packets
print(run1[10:30])  # prints 20 packets from the middle of the run

In interactive Python, returned objects are not printed, but rather their "representation" is printed (cf. the __repr__ method). The representation of PacketCollections is a listing of the number of packets, the "read id" (a.k.a. the run number), and the message associated with the PacketCollection when it was created.

Individual LArPix Packets

LArPix Packet objects represent individual LArPix UART packets. They have attributes which can be used to inspect or modify the contents of the packet.

packet = run1[0]
# all packets
packet.packet_type  # unique in that it gives the bits representation
packet.chip_id  # all other properties return Python numbers
packet.chip_key # key for association to a unique chip (can be None)
packet.parity
packet.downstream_marker

# data packets
packet.channel_id
packet.dataword
packet.timestamp
packet.trigger_type
packet.local_fifo
packet.shared_fifo
# config packets
packet.register_address
packet.register_data

Internally, packets are represented as an array of bits, and the different attributes use Python "properties" to seamlessly convert between the bits representation and a more intuitive integer representation. The bits representation can be inspected with the bits attribute.

Packet objects do not restrict you from adjusting an attribute for an inappropriate packet type. For example, you can create a data packet and then set packet.register_address = 5. This will adjust the packet bits corresponding to a configuration packet's "register_address" region, which is probably not what you want for your data packet.

Packets have a parity bit which enforces odd parity, i.e. the sum of all the individual bits in a packet must be an odd number. The parity bit can be accessed as above using the parity attribute. The correct parity bit can be computed using compute_parity(), and the validity of a packet's parity can be checked using has_valid_parity(). When constructing a new packet, the correct parity bit can be assigned using assign_parity().

Individual packets can be printed to show a human-readable interpretation of the packet contents. The printed version adjusts its output based on the packet type, so a data packet will show the data word, timestamp, etc., while a configuration packet will show the register address and register data.

Like with PacketCollections, Packets also have a "representation" view based on the bytes that make up the packet. This can be useful for creating new packets since a Packet's representation is also a vaild call to the Packet constructor. So the output from an interactive session can be copied as input or into a script to create the same packet.

With the v2 chip, more information about the internal fifo can be gathered by running with fifo diagonstics enabled on a given asic. In this case, the bits of each packet are to be interpreted differently. Each packet object can be set to be interpreted in this mode via the fifo_diagnostics_enabled flag. See the Packet_v2 documentation for more details.

Logging communications with LArPix ASICs using the HDF5Logger

To create a permanent record of communications with the LArPix ASICs, an HDF5Logger is used. To create a new logger

from larpix.logger import HDF5Logger
controller.logger = HDF5Logger(filename=None, buffer_length=10000) # a filename of None uses the default filename formatting
controller.logger.enable() # starts tracking all communications

You can also initialize and enable the logger in one call by passing the enabled keyword argument (which defaults to False):

controller.logger = HDF5Logger(filename=None, enabled=True)

Now whenever you send or receive packets, they will be captured by the logger and added to the logger's buffer. Once buffer_length packets have been captured the packets will be written out to the file. You can force the logger to dump the currently held packets at any time using HDF5Logger.flush()

controller.verify_configuration()
controller.logger.flush()

In the event that you want to temporarily stop tracking communications, the disable and enable commands do exactly what you think they might.

controller.logger.disable() # stop tracking
# any communication here is ignored
controller.logger.enable() # start tracking again
controller.logger.is_enabled() # returns True if tracking

Once you have finished your tests, be sure to disable the logger. If you do not, you will lose any data still in the buffer of the logger object. We strongly recommend wrapping logger code with a try, except statement if you can. Any remaining packets in the buffer are flushed to the file upon disabling.

controller.logger.disable()

Viewing data from the HDF5Logger

The HDF5Logger uses a format called LArPix+HDF5v1.0 that is specified in the larpix.format.hdf5format module (and documentation starting in v2.3.0). That module contains a to_file method which is used internally by HDF5Logger and a from_file method that you can use to load the file contents back into LArPix Control. The LArPix+HDF5 format is a "plain HDF5" format that can be inspected with h5py or any language's HDF5 binding.

To open the HDF5 file from python

import h5py
datafile = h5py.File('<filename>')

Within the datafile there is one group ('_header') and two datasets ('packets' and 'messages'). The header group contains some useful meta information about when the datafile was created and the file format version number, stored as attributes.

list(datafile.keys()) # ['_header', 'messages', 'packets']
list(datafile['_header'].attrs) # ['created', 'modified', version']

The packets are stored sequentially as a numpy mixed-type arrays within the rows of the HDF5 dataset. The columns refer to the element of the numpy mixed type array. The specifics of the data type and entries are set by the larpix.format.hdf5format.dtype object - see the larpix-control docs for more information. You can inspect a packet as a tuple simply by accessing its respective position within the HDF5 dataset.

raw_value = datafile['packets'][0] # e.g. (b'0-246', 3, 246, 1, 1, -1, -1, -1, -1, -1, -1, 0, 0)
raw_values = datafile['packets'][-100:] # last 100 packets in file

If you want to make use of numpy's mixed type arrays, you can convert the raw values to the proper encoding by retrieving it as a list (of length 1, for example) via

packet_repr = raw_values[0:1] # list with one element
packet_repr['chip_id'] # chip key for packet, e.g. 246
packet_repr['dataword'] # list of ADC values for each packet
packet_repr.dtype # description of data type (with names of each column)

You can also view entire "columns" of data:

# all packets' ADC counts, including non-data packets
raw_values['dataword']
# Select based on data type using a numpy bool / "mask" array:
raw_values['dataword'][raw_values['packet_type'] == 0] # all data packets' ADC counts

h5py and numpy optimize the retrieval of data so you can read certain columns or rows without loading the entire data file into memory.

Don't forget to close the file when you are done. (Not necessary in interactive python sessions if you are about to quit.)

datafile.close()

Running with a PACMANv1r1 board (v2 asic)

Before you can configure the system, you need to generate a configuration file for the PACMAN_IO interface. This sets up the mapping from chip keys to the ip addresses of the physical devices. One example configuration is provided in larpix/configs/io/pacman.json, which assumes that you can perform hostname DNS resolution.

After powering up the PACMAN board, you can create a new PACMAN io object with

from larpix import Controller
from larpix.io import PACMAN_IO
controller = Controller()
controller.io = PACMAN_IO(config_filepath='<io config file path>')
controller.load('<controller config file path>')
controller.io.ping() # returns a dict of (io_group, ping_success)

To set the correct supply voltages

controller.io.set_vddd() # set default vddd (~1.8V)
controller.io.set_vdda() # set default vdda (~1.8V)

These automatically query the built-in ADCs and return the set voltage and current in mV and mA, respectively. And to power on the chips

controller.io.enable_tile()

which will enable the LDOs for VDDD/VDDA and the driver chips / FPGA outputs for IO.

To bring up the Hydra network (and work around the known bugs in v2), do the following:

# First bring up the network using as few packets as possible
controller.io.group_packets_by_io_group = False # this throttles the data rate to avoid FIFO collisions
for io_group, io_channels in controller.network.items():
    for io_channel in io_channels:
        controller.init_network(io_group, io_channel)

# Configure the IO for a slower UART and differential signaling
controller.io.double_send_packets = True # double up packets to avoid 512 bug when configuring
for io_group, io_channels in controller.network.items():
    for io_channel in io_channels:
        chip_keys = controller.get_network_keys(io_group,io_channel,root_first_traversal=False)
        for chip_key in chip_keys:
            controller[chip_key].config.clk_ctrl = 1
            controller[chip_key].config.enable_miso_differential = [1,1,1,1]
            controller.write_configuration(chip_key, 'enable_miso_differential')
            controller.write_configuration(chip_key, 'clk_ctrl')
for io_group, io_channels in controller.network.items():
    for io_channel in io_channels:
        controller.io.set_uart_clock_ratio(io_channel, 4, io_group=io_group)

controller.io.double_send_packets = False
controller.io.group_packets_by_io_group = True

At this point, you can happily interface with the ASICs using everything you learned above. I also recommend you glance at the section below (Running with a Bern DAQ board), which describes some shortcut functions available in the Controller class. In particular, it is good practice to verify_configuration before proceeding with anything.

Running with a Bern DAQ board (v1 asic)

Since you have completed the tutorial with the FakeIO class, you are now ready to interface with some LArPix ASICs. If you have a Bern DAQ v2-3 setup you can follow along with the rest of the tutorial.

Before you can configure the system, you will need to generate a configuration file for the ZMQ_IO or MultiZMQ_IO interface. This provides the mapping from chip keys to physical devices. In the case of the ZMQ interface, it maps io group #s to the IP address of the DAQ board. A number of example configurations are provided in the installation under larpix/configs/io/<config name>.json, which may work for your purposes. We recommend reading the docs about how to create one of these configuration files. By default the system looks for configuration in the pwd, before looking for the installation files. If you only have one DAQ board on your network, likely you will load the io/daq-srv<#>.json configuration.

With the DAQ system up and running

>>> from larpix import Controller
>>> from larpix.io import ZMQ_IO
>>> controller = Controller()
>>> controller.io = ZMQ_IO(config_filepath='<path to config>')
>>> controller.load('controller/pcb-<#>_chip_info.json')
>>> controller.io.ping()
>>> for key,chip in controller.chips.items():
...     chip.config.load('chip/quiet.json')
...     print(key, chip.config)
...     controller.write_configuration(key)
>>> controller.run(1,'checking the data rate')
>>> controller.reads[-1]
<PacketCollection with 0 packets, read_id 0, 'checking the data rate'>

This should give you a quiet state with no data packets. Occasionally, there can be a few packets left in one of the system buffers (LArPix, FPGA, DAQ server). A second run command should return without any new packets.

If you are using the v1.5 anode, you may need to reconfigure the miso/mosi mapping (since the miso/mosi pair for a daisy chain is not necessarily on a single channel). To do this, pass a miso_map or mosi_map to the ZMQ_IO object on initialization:

>>> controller.io = ZMQ_IO(config_filepath='<path to config>', miso_map={2:1}) # relabels packets received on channel 2 as packets from channel 1

Check configurations

If you are still receiving data, you can check that the hardware chip configuration match the software chip configurations with

>>> controller.verify_configuration()
(True, {})

If the configuration read packets don't match the software chip configuration, this will return

>>> controller.verify_configuration()
(False, {<register>: (<expected>, <received>), ...})

Missing packets will show up as

>>> controller.verify_configuration()
(False, {<register>: (<expected>, None), ...})

If your configurations match, and you still receive data then you are likely seeing some pickup on the sensor from the environment -- good luck!

Enable a single channel

>>> chip_key = '1-1-3'
>>> controller.disable() # mask off all channel
>>> controller.enable(chip_key, [0]) # enable channel 0 of chip

Set the global threshold of a chip

>>> controller.chips[chip_key].config.global_threshold = 40
>>> controller.write_configuration(chip_key)
>>> controller.verify_configuration(chip_key)
(True, {})

Inject a pulse into a specific channel

>>> controller.enable_testpulse(chip_key, [0]) # connect channel 0 to the test pulse circuit and initialize the internal DAC to 255
>>> controller.issue_testpulse(chip_key, 10) # inject a pulse of size 10DAC by stepping down the DAC
<PacketCollection with XX packets, read_id XX, "configuration write">
>>> controller.disable_testpulse(chip_key) # disconnect test pulse circuit from all channels on chip

You will need to periodically reset the DAC to 255, otherwise you will receive a ValueError once the DAC reaches the minimum specified value.

>>> controller.enable_testpulse(chip_key, [0], start_dac=255)
>>> controller.issue_testpulse(chip_key, 50, min_dac=200) # the min_dac keyword sets the lower bound for the DAC (useful to avoid non-linearities at around 70-80DAC)
<PacketCollection with XX packets, read_id XX, "configuration write">
>>> controller.issue_testpulse(chip_key, 50, min_dac=200)
ValueError: Minimum DAC exceeded
>>> controller.enable_testpulse(chip_key, [0], start_dac=255)
>>> controller.issue_testpulse(chip_key, 50, min_dac=200)
<PacketCollection with XX packets, read_id XX, "configuration write">

Enable the analog monitor on a channel

>>> controller.enable_analog_monitor(chip_key, 0) # drive buffer output of channel 0 out on analog monitor line
>>> controller.disable_analog_monitor(chip_key) # disable the analog monitor on chip

While the software enforces that only one channel per chip is being driven out on the analog monitor, you must disable the analog monitor if moving between chips.

Miscellaneous implementation details

Endian-ness

We use the convention that the LSB is sent out first and read in first. The location of the LSB in arrays and lists changes from object to object based on the conventions of the other packages we interact with.

In particular, pyserial sends out index 0 first, so for bytes objects, index 0 will generally have the LSB. On the other hand, bitstrings treats the last index as the LSB, which is also how numbers are usually displayed on screen, e.g. 0100 in binary means 4 not 2. So for BitArray and Bits objects, the LSB will generally be last.

Note that this combination leads to the slightly awkward convention that the least significant bit of a bytestring is the last bit of the first byte. For example, if bits[15:0] of a packet are 0000 0010 0000 0001 ( = 0x0201 = 513), then the bytes will be sent out as b'\x01\x02'.

The Configuration object

The Configuration object represents all of the options in the LArPix configuration register. Each row in the configuration table in the LArPix datasheet has a corresponding attribute in the Configuration object. Per-channel attributes are stored in a list, and all other attributes are stored as a simple integer. (This includes everything from single bits to values such as "reset cycles," which spans 3 bytes.)

Configuration objects also have some helper methods for enabling and disabling per-channel settings (such as csa_testpulse_enable or channel_mask). The relevant methods are listed here and should be prefixed with either enable_ or disable_:

• channels enables/disables the channel_mask register
• external_trigger enables/disables the external_trigger_mask register
• testpulse enables/disables the csa_testpulse_enable register
• analog_monitor enables/disables the csa_monitor_select register

Most of these methods accept an optional list of channels to enable or disable (and with no list specified acts on all channels). The exception is enable_analog_monitor (and its disable counterpart): the enable method requires a particular channel to be specified, and the disable method does not require any argument at all. This is because at most one channel is allowed to have the analog monitor enabled.

The machinery of the Configuration object ensures that each value is converted to the appropriate set of bits when it comes time to send actual commands to the physical chip. Although this is not transparent to you as a user of this library, you might want to know that two sets of configuration options are always sent together in the same configuration packet:

• csa_gain, csa_bypass, and internal_bypass are combined into a single byte, so even though they have their own attributes, they must be written to the physical chip together

• test_mode, cross_trigger_mode, periodic_reset, and fifo_diagnostic work the same way

Similarly, all of the per-channel options (except for the pixel trim thresholds) are sent in 4 groups of 8 channels.

Configurations can be loaded by importing larpix.configs and running the load function. This function searches for a configuration with the given filename relative to the current directory before searching the "system" location (secretly it's in the larpix/configs/ folder). This is similar to #include "header.h" behavior in C.

Configurations can be saved by calling chip.config.write with the desired filename.

Once the Chip object has been configured, the configuration must be sent to the physical chip.