Command reference¶

The server speaks a line-oriented ASCII protocol over TCP. Commands are short mnemonics with space-separated arguments; replies are plain text.

The port¶

camerad opens exactly one TCP port, BLKPORT (camerad/camerad.cpp). The connection stays open for as long as the client holds it, so it works directly with telnet as an ad hoc command line, and the reply on the same connection is what signals completion.

Each client connection is served on its own thread. A socket that sits idle is closed after 3 seconds (utils/network.h).

Warning

Older configuration files and the superseded 2022 ICD describe two more ports: a non-blocking command port (NBPORT) and a UDP multicast port for asynchronous status messages (ASYNCPORT, ASYNCGROUP). Neither exists in camerad 2.0.

NBPORT is read only by the emulator. ASYNCPORT and ASYNCGROUP are read by nothing: the UDP multicast class still exists in utils/network.cpp but is never instantiated, so no asynchronous messages are ever sent. Setting those keys has no effect.

Replies¶

A reply is the command’s return value, if any, followed by DONE or ERROR:

exptime 1.5
1.500 DONE

expose
DONE

bogus
ERROR

ERROR means the server rejected or failed the command. With LONGERROR=true the reply carries a human-readable reason as well.

Two commands break the pattern: a command invoked with ? returns its syntax with no DONE suffix, and commands that reply with JSON return the JSON document alone.

Warning

DONE reports on the command, not on the frame outputs. expose returns DONE once the exposure and readout complete, whether or not the FITS writer kept up. See frame outputs.

Command tables¶

Note

The base command table is generated from the server’s dispatch chain and cross-checked against the descriptions kept alongside the docs, so a command the server gains or loses without a matching description fails the documentation build.