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gr-fosphor

GPU-drawn real-time spectrum and waterfall display blocks for GNU Radio

What it does

Adds fosphor sink blocks to GNU Radio Companion: a spectrum display and a waterfall computed and drawn on the graphics card through OpenCL and OpenGL, fast enough to show tens of MHz of bandwidth as a smooth live picture with a persistence ("phosphor") trace. There is a Qt sink for use inside a Qt GUI flow graph and a GLFW sink that opens its own window, plus an overlap block for the FFT input.

Why you would want it

A CPU-drawn FFT display in GNU Radio stutters or drops samples at the wide sample rates a HackRF, bladeRF or USRP can deliver. fosphor moves the FFT and the drawing to the GPU, so a wide band can be watched live, and its persistence view shows short bursts that a normal waterfall averages away. It is the display most GNU Radio demonstrations use. It is an alternative to GNU Radio's own QT GUI Frequency and Waterfall sinks, which need no GPU.

Before it will work

GNU Radio (it arrives as a dependency) and a working OpenCL platform with OpenGL on the same device, which apt does NOT install for you. Install the OpenCL driver for your graphics hardware and check it with clinfo before opening a flow graph. The 2026-09-30 sweep found mesa-opencl-icd, pocl-opencl-icd and clinfo offered on Debian 13, Parrot and Ubuntu 24.04; Intel's own intel-opencl-icd was offered on Ubuntu 24.04 and not in the main component of Debian 13 or Parrot. Which one works with fosphor on which GPU is unmeasured here.

How it installs

  • apt: gr-fosphor
  • The .deb Depends on gnuradio-dev (read from Debian 13's control file, 2026-09-30), so installing it pulls GNU Radio's development headers as well as GNU Radio. Its library Depends on ocl-icd-libopencl1 | libopencl1, which is the OpenCL loader only: no OpenCL driver for any GPU comes with it.

Known problems

Unmeasured on any machine here, including the field laptop's Intel Iris Xe: no fosphor block has been run. Its dependencies name only the OpenCL loader, so nothing at install time notices a machine with no OpenCL driver; that shows up when a flow graph with a fosphor sink starts. The install is larger than the package suggests, because it pulls gnuradio-dev. Upstream has had no commit since 2024-03-23.

Keeping it current

  • probe: apt policy
  • strategy: apt_upgrade
  • Upstream moves rarely; the last commit on the default branch is from 2024-03-23 and the archive packages it. A newer snapshot arrives through the distribution or not at all.

Where to get help with the software itself

Osmocom. The README names the documentation at https://osmocom.org/projects/sdr/wiki/Fosphor, the SDR section of the Osmocom discourse forum, the osmocom-sdr mailing list, and the issue tracker at https://osmocom.org/projects/sdr/issues.

Source: catalog/packages/gr-fosphor.yaml