epicsdev

epicsdev is a small Python toolkit for building EPICS PVAccess servers with p4p.

It is intended for fast development of simulated devices, instrument front ends, and stress-test servers that publish scalars, waveforms, and images.

Background reading: Why Python-based servers are essential for large EPICS facility like future EIC

What epicsdev provides

• A simple API for defining and hosting PVs
• Built-in IOC-style helper PVs for status and basic statistics
• Autosave/restore of writable PV values
• Optional logging of put operations to a separate PV
• Example applications for waveforms, images, and text logging

In practice, it combines a Python helper library with a few services commonly expected from EPICS IOCs:

• Autosave: save writable PV values and restore them on restart
• IOC-stats-style PVs: host name, uptime, heartbeat, CPU load, and related PVs
• Put logging: optional forwarding of put activity to a logging PV

Package contents

Installation

Install the base package:

python -m pip install epicsdev

Optional tools for GUI pages and plotting:

python -m pip install pypeto pvplot

Quick start

Start the built-in demo server:

python -m epicsdev.epicsdev

The demo uses the default PV prefix:

epicsDev0:

Open the example control page

python -m pypeto -c config -f epicsdev

This page gives you:

• basic server control
• live parameter monitoring
• waveform plotting helpers

Screenshots:

• pypeto control page
• pvplot example

Phoebus display

An example Phoebus display file is included at config/epicsdev.bob. Screenshot: Phoebus display

Minimal programming model

The typical workflow is:

1. define PVs
2. initialize the server with init_epicsdev()
3. start a p4p.server.Server
4. publish updates from your polling loop

PV definitions are lists with this shape:

[name, description, initial_value, extra]

Where extra is optional and may include keys such as:

• features: PV features such as writable or discrete
• type: explicit EPICS type, for example u32 or f32
• units: engineering units
• limitLow, limitHigh: write limits
• setter: callback invoked on writes
• valueAlarm: value alarm configuration

Normative Type (NT) selection from initial_value

epicsdev selects the underlying PV normative type from initial_value (unless overridden by extra["type"]).

Current behavior:

Type-code mapping follows p4p scalar codes (for example i32, u32, f32, f64, s8, ...). You can force a specific type using extra["type"].

Examples:

• 42 -> NTScalar(i32)
• 3.14 -> NTScalar(f32)
• [1, 2, 3] -> NTScalarArray(i32)
• ['OFF', 'ON'] with {"features": "D"} -> NTEnum
• np.zeros((120, 120), dtype=np.int16) -> NTNDArray

Notes:

• For discrete PVs (D), autosave stores the enum index rather than the choice text, so updated choice lists can still be restored predictably.
• For iterable non-NumPy values, keep the initial sequence non-empty so element type inference is unambiguous.

Minimal example:

from p4p.server import Server
from epicsdev.epicsdev import init_epicsdev, publish, pvv, set_server, sleep

pv_defs = [
   ["temperature", "Simulated temperature", 25.0, {"features": "W", "units": "C"}],
   ["waveform", "Example waveform", [0.0], {"units": "V"}],
]

pvs = init_epicsdev("demo0:", pv_defs, verbose=1)
server = Server(providers=[pvs])
set_server("Start")

while True:
   publish("temperature", pvv("temperature") + 0.01)
   if not sleep():
      pass

Example applications

epicsdev.imagegen

imagegen generates synthetic 2D images with a grid of Gaussian blobs and optional per-row PVs.

It publishes:

• a noisy image
• PVs that control image size, blob count, blob width, and noise level
• 10,000 of dynamicaly-changed waveform int16 PVs, each representing 1000-point row.
• The publishing performance is 55,000 of PVs per second (110 MB/s).

The generated data is intended for high-throughput testing of EPICS clients, transport, and visualization tools.

example

epicsdev.putlog

putlog hosts a writable PV named dump and appends received text to a file.

Start the logger:

python -m epicsdev.putlog /tmp/putlog.txt

By default, the logger prefix is:

putlog0:

Write text to it with:

pvput putlog0:dump "hello from client"

Notes on autosave and helper PVs

When you initialize a server with init_epicsdev(), epicsdev automatically adds a standard set of helper PVs before your application-specific PVs. These include PVs such as:

• HOSTNAME
• VERSION
• HEARTBEAT
• UPTIME
• CPU_LOAD
• status
• server
• verbose
• sleep
• cycle
• cycleTime

Writable PV values can be stored in an autosave file and restored on restart. This makes epicsdev practical for interactive development and lab setups where operator-tuned values should survive process restarts.

AI-assisted device support workflow

epicsdev is intentionally small and explicit, which makes it convenient for AI-assisted code generation and device support prototyping.

Typical workflow:

1. identify a device API or programming manual
2. define PVs and their setter callbacks
3. generate a first server implementation from an existing epicsdev example
4. review, test, and refine

One example built this way is epicsdev_tektronix.

Requirements

• Python 3.7+
• p4p>=4.2.2
• psutil

Optional:

• pypeto
• pvplot
• Phoebus for .bob display files