nuttx-apps/system/psmq/README.md

System / psmq Publish Subscribe Message Queue

psmq is publish subscribe message queue. It's a set of programs and libraries to implement publish/subscribe way of inter-process communication on top of POSIX message queue.

Manuals, source code and more info at: https://psmq.kurwinet.pl

Little demo using psmqd broker, psmq_pub and psmq_sub:

Start broker and make it log to file

nsh> psmqd -b/brok -p/sd/psmqd/psmqd.log

Start subscribe thread that will read all messages send on /can/* topic

nsh> psmq_sub -n/sub -b/brok -t/can/* -o/sd/psmq-sub/can.log
n/connected to broker /brok
n/subscribed to /can/*
n/start receiving data

Publish some messages

nsh> psmq_pub -b/brok -t/can/engine/rpm -m50
nsh> psmq_pub -b/brok -t/adc/volt -m30
nsh> psmq_pub -b/brok -t/can/room/10/temp -m23
nsh> psmq_pub -b/brok -t/pwm/fan1/speed -m300

Check out subscribe thread logs

nsh> cat /sd/psmq-sub/can.log

[1970-01-01 00:00:53] topic: /can/engine/rpm, priority: 0, paylen: 3, payload:
[1970-01-01 00:00:53] 0x0000  35 30 00                                         50.
[1970-01-01 00:00:58] topic: /can/room/10/temp, priority: 0, paylen: 3, payload:
[1970-01-01 00:00:58] 0x0000  32 33 00                                         23.

As you can see /adc/volt and /pwm/fan1/speed haven't been received by subscribe thread.

Content:

• psmqd – broker, relays messages between clients.
• psmq_sub – listens to specified topics, can be used as logger for communication (optional).
• psmq_pub – publishes messages directly from shell. Can send binary data, but requires pipes, so on nuttx it can only send ASCII.
• libpsmq – library used to communicate with the broker and send/receive messages.