modemu2k is a Hayes-style AT-command modem emulator that bridges a serial-style interface to a TCP or Telnet endpoint. It ships as a C library (libmodemu2k) exposing the modem state machine, plus a small CLI built on top that allocates a PTY and either reads stdin/stdout directly, forks a comm program (minicom, picocom) on the slave, or accepts an incoming TCP connection as the TTY. IPv4 and IPv6. It is based on modemu, originally developed by Toru Egashira (1995–1996).
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Recent Releases
0.2.231 May 2026 04:50
major feature:
* Fix pkg-config Cflags so consumers can `#include `
(was forcing the namespaced `` form)
* Fix interactive ATZ wiping the -v verbose mask mid-session; add
m2k_set_force_verbose / m2k_get_force_verbose public API for hosts
that want narration regardless of AT V state
0.2.130 May 2026 00:17
major feature:
* Add -v/--verbose flag (CLI). -v previously meant --version,
which now requires -V (breaking)
* Fix at q to actually quit (regression from v0.2.0)
* Ctrl-C twice in CMD mode quits (CMD only; online mode
unaffected)
* m2k-minicom / m2k-picocom helper scripts forward arbitrary
args to modemu2k
2026-05-27
- modemu2k (v0.2.0)
* Refactor core into libmodemu2k; public API in modemu2k.h at the
project root, with M2K_API visibility markers on every public
function and M2K_VERSION_* macros + m2k_version() for
header/library skew detection
* Add steppable event-loop API (m2k_get_pollfds, m2k_step,
m2k_run_done, plus M2K_STATE_DIAL for non-blocking ATD) and
embed-mode I/O (m2k_setup_app_io, m2k_write_from_app,
m2k_read_to_app) so a host program can run modemu2k inside its
own poll/epoll loop with the host supplying the TTY-side bytes
* Add curl-style per-context error reporting: m2k_set_error_buffer
with M2K_ERROR_BUFFER_SIZE, m2k_strerror, and the M2K_ERR_*
codes (including M2K_ERR_AT for rejected AT commands and
M2K_ERR_WOULDBLOCK for flow-control retry)
* Add m2k_escape, m2k_is_online, m2k_has_carrier, m2k_get_listen_fd,
and m2k_set_dtr/_rts (with matching getters) for embed-mode
hosts; DTR 1 0 while a connection is live hangs up
( D2-equivalent)
* Add TCP listen mode (-l/--listen ) for use as a virtual
modem backend (issue #32)
* Print --help output and exit when invoked with no arguments;
reject conflicting -c/-d/-l/-s combinations at parse time
instead of silently honoring the last one
* Wrap modemu2k.h declarations in extern "C" guards for C++ consumers
* Per-ctx state separation: +++ escape detector, line buffer, and
telnet option negotiation tables moved into m2k_t so two
coexisting contexts no longer share/clobber each other
* Detect POSIX PTY allocation via meson at configure time, fixing
PTY setup on macOS and FreeBSD which the previous compile-
0.0.620 Jun 2020 13:05
minor feature:
For compiling on gcc-10.
0.0.524 Aug 2019 03:15
minor feature:
IPv6 connections can now be made.
.
To specify a non-standard port, you must use a space now instead of.
a colon
.
Replaced obsolete gethostbyname() with getaddrinfo().
.
If the m2k-minicom.sh script is run from the scripts/ directory, it will.
use the dev build of modemu2k in src/.
0.0.418 Aug 2019 06:37
minor feature:
* Fixed --version output
* Added script to invoke minicom: 'm2k-minicom.sh'
* Infrastructure to implement testing with `make check` added.
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