pycbsdk

Pure Python package for communicating with Blackrock Cerebus devices

Quick Start

From a shell...

pip install pycbsdk

Then in python

from pycbsdk import cbsdk

params_obj = cbsdk.create_params()
nsp_obj = cbsdk.get_device(params_obj)  # NSPDevice instance. This will be the first argument to most API calls. 
runlevel = cbsdk.connect(nsp_obj)  # Bind sockets, change device run state, and get device config.
config = cbsdk.get_config(nsp_obj)
print(config)

You may also try the provided test script with python -m pycbsdk.examples.print_rates or via the shortcut: pycbsdk_print_rates.

Introduction

pycbsdk is a pure Python package for communicating with a Blackrock Neurotech Cerebus device. It is loosely based on Blackrock's cbsdk, but shares no code nor is pycbsdk supported by Blackrock.

pycbsdk's API design is intended to mimic that of a C-library. Indeed, a primary goal of this library is to help prototype libraries in other languages. After all, Python is a poor choice to handle high throughput data without some compiled language underneath doing all the heavy lifting.

However, it's pretty useful as is! And so far it has been good-enough for some quick test scripts, and it even drops fewer packets than CereLink. So, please use it, and contribute! We are more than happy to see the API expand to support more features, or even to have an additional "pythonic" API.

Design

Upon initialization, the NSPDevice instance configures its sockets (but no connection yet), it allocates memory for its mirror of the device state, and it registers callbacks to monitor config state.

When the connection to the device is established, two threads are created and started:

• CerebusDatagramThread
  • Makes heavy use of asyncio
  • A Receiver Coroutine retrieves datagrams, slices into generic packets, enqueues them in the receiver queue
  • A Sender Coroutine monitors a sender queue and immediately sends found packets.
• PacketHandlerThread
  • Monitors the receiver queue.
  • Updates device state (e.g., mirrors device time)
  • Materializes the generic packets into specific packets.
  • Calls registered callbacks depending on the packet type.

connect() has startup_sequence=True by default. This will cause the SDK to attempt to put the device into a running state. Otherwise, it'll stay in its original run state.

After the connection is established, the client can use API functions to:

• Get / Set config
  • set_config and set_channel_config do not do anything yet
  • set_channel_spk_config and set_channel_config_by_packet do things and are blocking.
  • get_config is non-blocking by default and will simply read the local mirror of the config. However, if force_refresh=True is passed as a kwarg, then this function will block and wait for a reply from the device. Use this sparingly.
• Register a callback to receive data as soon as it appears on the handler thread.

This and more should appear in the documentation at some point in the future...

Limitations

• This library takes exclusive control over the UDP socket on port 51002 and thus cannot be used with Central, nor any other instance of pycbsdk. You only get one instance of pycbsdk or Central per machine.
  • CereLink's cerebus.cbpy uses shared memory and therefore can work in parallel to Central or other cbpy instances.
• The API is still very sparse and limited in functionality.
• For now, Python still has the GIL. This means that despite using threading, if your callback functions are slow and hold up the PacketHandlerThread, this could hold up datagram retrieval and ultimately cause packets to be dropped.
  • Callbacks may enqueue the data for a longer-running multiprocessing process to handle.
  • Switch to No GIL Python as soon as it is available.
  • Use pycbsdk to prototype an application in a language that uses real parallelism.