Open TimeCard Mini: Turning a Raspberry Pi CM4 into a PCIe Time Source

Why this combination

When the Raspberry Pi Compute Module 4 launched in 2020 with industrial-grade temperature options, ECC memory and PCIe support, it opened up embedded and edge deployments where a full server is impractical. The constraint that remained was precision timing — the CM4's on-board Ethernet doesn't have the hardware timestamping precision that PTP-grade applications need, and an external grandmaster appliance defeats the purpose of using a compact embedded platform in the first place.

The Open TimeCard Mini was designed specifically to close this gap. It slots into a CM4 carrier board via PCIe, providing the hardware-grade GNSS receiver, precision oscillator and PTP timestamping engine that the CM4 doesn't have natively. The combination delivers commercial-grade timing precision in a footprint smaller than a paperback book.

What's on the card

The Mini includes a multi-band GNSS receiver (typically L1+L5 or L1+L2C, depending on the variant), a temperature-compensated or oven-controlled crystal oscillator depending on the holdover requirement, a hardware PTP timestamping engine, and the PCIe interface for CM4 integration. It runs the linuxptp software stack from the CM4 host, exposing time as a hardware reference clock that the host application can read directly and as a PTP grandmaster that other devices on the local network can lock to.

The form factor is intentionally compact. The card is designed to fit inside small embedded enclosures alongside a CM4 carrier board, not to be the primary component of a rack-mounted system. For deployments that need precision timing in a space too small for a 1U appliance, this is the answer.

Where it lives in production

Edge computing platforms where each site needs a local precision time reference. Distributed sensor networks for environmental monitoring, infrastructure monitoring or industrial control. Embedded instruments where the timing source has to be physically integrated with the measurement hardware. Compact test and measurement systems. Mobile and field-deployable measurement platforms. Educational labs and research deployments where the cost of a full grandmaster appliance is a barrier.

Each of these use cases has different specific requirements, but they share the common thread of needing PTP-grade timing in a footprint and at a cost point that traditional grandmaster hardware can't address.

Where TimeBeat fits

TimeBeat ships the Open TimeCard Mini alongside the standard Open TimeCard, the Open Time Appliance and the Open Time Node WR — each variant targeting a different deployment context. The Mini is the right answer for embedded and edge deployments where the form factor and price point are binding constraints. For larger deployments, the standard variants are still the right starting point. Talk to the engineering team if you're trying to figure out which variant fits your specific use case.