This page is about the "production" version of the setup described in ICE40_based_passive_tap.

It is a bi-directional, high-impedance passive tap for E1 (PRI/S2M) tracing. It traces both directions of a link simultaneously via two LIU (Line Interface Units) attached to an iCE40 FPGA with E1 framer + USB softcores.

The traces are sent as isochronous USB transfers to the host PC, where they can (for example) be stored on disk.


Hardware files can be found at: and are available as Open Source Hardware.

design files

We originally started with a prototype from an iCE40 evaluation board plus two osmo-e1-xcvr and one e1-tap as described in ICE40_based_passive_tap.

Meanwhile, we have designed a fully integrated board. Design files are part of the osmo-e1-hardware.git repository.

gateware + firmware

The FPGA gateware and RISC-V softcore firmware are found in the osmo-e1-hardware.git repository, under the gateware and firmware/ice40-riscv/e1-tracer directories respectively.


Fully assembled products based on this hardware are going to be made available by sysmocom


The host software is found in the e1-recorder branch of ice40playground.git, see

There are two related programs:

  • main - the program used to perform recordings and store them
  • dump - the program to analyze recordings
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