EPICS IOC for the PicoQuant HydraHarp 400

Introduction

The HydraHarp 400 is advertized as a "multichannel picosecond event timer module" by its manufacturer, PicoQuant GmbH in Germany.

This is an EPICS Input-Output Controller (IOC) application for the HydraHarp. It uses the EMMI API, which in turn uses Diamond Light Source's EPICS wrapper pythonSoftIOC (as of September 2023). This means that miniquant-ioc's EPICS CA stack is essentially the "original" C/C++ implementation, merely interfaced by Python.

The hardware access layer is being published as miniquant -- a truly Python'esque :) API layer on top of the proprietary HydraHarp API of PicoQuant, but without the EPICS specific code.

Installation

Miniquant-ioc itself is installed fairly easy via PyPI:

pip install miniquant-ioc

Or via direct clone from Gitlab:

git clone https://gitlab.com/codedump2/miniquant-ioc \
    && pip install ./miniquant-ioc

If miniquant (the API layer) is not already installed, it will be automatically pulled from PyPI as a dependency of miniquant-ioc. In that case, you will most certainly have to go through a mildly elaborate set of post-install procedures to make sure that miniquant is, in fact, able to find and access your HydraHarp. (This is owing for one to the proprietary nature of the original PicoQuant C/C++ API for the HydraHarp, and for another to the fact that the HydraHarp 400 has a quirky USB controller; it works with any modern upstream Linux kernel, but requires specialized kernel boot parameter or USB driver module settings.)

Configuration

A specific IOC configuration file is necessary to run the Miniquant IOC. By default, the IOC loads its configuration from /etc/miniquant/harp.yaml, but that behaviour can be overridden using the -c or --harp-config command line parameter of miniquant-ioc.

The PyPI installation might have placed a copy of a usable harp.yaml in your /etc/miniquant/... directory. If it hasn't, obtain one e.g. from here.

The configuration file has two distinct sets of options, organized in as many top-level YAML sections:

• harp: general HydraHarp device settings, like measurement mode, histogram size and resolution, offsets and zero-crossing levels; contains the following subkeys:

  • device: should have a string as value with one of "first", "any", or a HydraHarp device; the IOC will only connect to the device as specified ("first" and "any" is a good choice if you have only one device attached to a computer's USB ports)

  • presets:

  • settings:

• epics: application settings that directly influence the IOC behavior; in turn, these are divided in:

  • prefix: single key, contains the EPICS prefix as a string value

  • defaults: default settings to be used for all exported properties, can individually be overridden

  • harpBase: contains PV definitions all non channel specific properties of a HydraHarp device to export as PVs (stuffed in a subsection exports),

  • harpChannels: contains PV definitions for all channel specific properties. The subkey interfix contains a string to use in naming the channel-specific PVs (should contain {} format specifier for the channel index), and an exports section with actual PV definitions.

• IOC-specific settings about which properties to export as process variables (PVs).

Running