P25Time is a single-binary radio clock built on top of DSD-Neo. It listens to a P25 Phase 1 control channel, decodes Synchronization Broadcast messages, and serves the recovered radio time as an NTP source.

• Tunes a P25 Phase 1 control channel from an SDR input source.
• Decodes Synchronization Broadcast TSBKs (opcode 0x30).
• Reconstructs UTC from the control channel time payload.
• Serves that time over embedded NTP on UDP/123.
• Prints concise sync lines instead of the full DSD-Neo decode stream.

Example sync output:

SYNC 2026-03-18 00:38:52.50 UTC LTO=-5:00

• P25Time is unsynchronized until it sees a valid radio time broadcast.
• Once synchronized, it answers NTP as a stratum-1 source with refid P25T.
• By default it binds to 0.0.0.0:123, so run it as root or grant CAP_NET_BIND_SERVICE.

sudo ./P25Time -i rtl:0:771.18125M

Supported input examples:

sudo ./P25Time -i rtl:0:771.18125M
sudo ./P25Time -i rtl:0:771.18125M:22:0:24:0:2
sudo ./P25Time -i rtltcp:127.0.0.1:1234:771.18125M

You can verify the server replies to NTP with nc:

(printf '\x23'; dd if=/dev/zero bs=1 count=47 2>/dev/null) | nc -u -w1 127.0.0.1 123 | wc -c

A successful reply returns 48.

To inspect the raw packet:

(printf '\x23'; dd if=/dev/zero bs=1 count=47 2>/dev/null) | nc -u -w1 127.0.0.1 123 | xxd -g1

Add this to /etc/chrony/chrony.conf:

server 127.0.0.1 minpoll 4 maxpoll 4 iburst prefer

Then restart chrony:

sudo systemctl restart chronyd  # or chrony depending on distro
chronyc sources -v
chronyc tracking

systemd-timesyncd is an SNTP client, not a full NTP daemon, but you can still point it at P25Time:

[Time]
NTP=127.0.0.1

Then restart it:

sudo systemctl restart systemd-timesyncd

cmake -S . -B build
cmake --build build -j

The binary is produced at:

build/apps/dsd-cli/P25Time

• Built with DSD-Neo components.
• Current focus is P25 Phase 1 control-channel time recovery and embedded NTP service.
• Full validation passed in this tree: 251/251 tests.

This repository inherits the licensing and notices from the underlying DSD-Neo codebase. See the existing license and copyright files in this repository.