Altirra 850 Modem Reference

This reference describes how the host launcher configures Altirra, the emulated 850, and the modem path used by Mutineer. Source of truth: tools/run_altirra_850.py, tools/run_mutineer_telnet_test.py, and tools/run_mms_hatabs_probe.py.

Runtime Path

The intended emulated communications path is:

Atari BASIC/CIO -> MMS HATABS -> R: -> RHND850.COM -> Altirra 850 -> modem device -> host TCP

The generated Altirra profile uses an 850 device with baudex=true and emulevel=1. In Altirra source and behavior, that mode provides the stub-loader path while keeping the HLE R: handler available. The modem device is attached as a child of the 850 bus.

Profile Generation

tools/run_altirra_850.py writes a portable Altirra INI under results/altirra-850/, then copies it to tools/altirra/4.40/Altirra.ini. The portable registry root must be:

User\Software\virtualdub.org\Altirra

Altirra ignores portable sections that are not rooted under User\ or Shared\, so profile sections must keep that prefix.

The profile mounts:

• the selected ATR as D1:;
• third_party/SDX450_maxflash8.car, unless MUTINEER_USE_SDX=0;
• MUTINEER_EXTRA_DISK, when set.

Launch Commands

Launch the current versioned ATR:

make altirra-850-run

Launch a specific ATR:

MUTINEER_ATR=source/atr/atari-mutineer-v1.1.154.atr make altirra-850-run

Connect from the host to the default modem listener:

telnet 127.0.0.1 6507

Environment Variables

tools/run_altirra_850.py:

• MUTINEER_ATR: ATR path. Default is the current versioned ATR.
• MUTINEER_MODEM_PORT: host modem port. Default 6507.
• MUTINEER_CONNECT_RATE: Altirra modem connection rate. Default 2400.
• MUTINEER_TELNET: enable telnet negotiation in the modem profile.
• MUTINEER_TELNETLF: enable Altirra telnet LF handling.
• MUTINEER_USE_SDX: mount SDX cartridge when truthy. Default 1.
• MUTINEER_CART: override cartridge image path.
• MUTINEER_CART_MAPPER: override cartridge mapper string.
• MUTINEER_EXTRA_DISK: mount a second ATR/disk image.
• MUTINEER_ALTIRRA_DEBUG_LOG: write Altirra debug output to a chosen path.

Runtime tests also use:

• MUTINEER_ALTIRRA_DEBUG: when truthy, write per-run Altirra debug logs.
• MUTINEER_CONNECT_DELAY: wait before connecting to the emulated modem.
• MUTINEER_SEND_DELAY: delay between scripted telnet sends.
• MUTINEER_TEST_TIMEOUT: telnet test timeout.
• MUTINEER_XMODEM_TIMEOUT: XMODEM test timeout.

Baud Settings

The host modem profile defaults to connect_rate=2400. MMS defaults its R: XIO 36 baud code to 12, also documented as 2400 in mms/src/config.inc.

Atari BASIC can set the MMS baud code used by the next MMS_MOPEN:

MBASE=PEEK(1004)+256*PEEK(1005)
MBAUD=MBASE+90:MBCODE=MBASE+156
R=USR(MBAUD,13):REM 4800 ON NEXT MOPEN
POKE MBCODE,14:REM 9600 ON NEXT MOPEN

Keep the Altirra modem MUTINEER_CONNECT_RATE and the MMS R: baud code aligned when testing speed-sensitive behavior.

Listener And Outbound Modes

The normal BBS test path uses a host listener on MUTINEER_MODEM_PORT. MMS HATABS probe ATRs can also use outbound mode: the Atari-side probe dials ATDI <host> <port>, and the host test accepts the connection.

Probe-specific dial variables:

• MMS_PROBE_DIAL_HOST: default 127.0.0.1.
• MMS_PROBE_DIAL_PORT: default MUTINEER_MODEM_PORT or 6507.
• MMS_HATABS_PROBE_CONNECT_MODE: default outbound.

Result Files

Manual Altirra launcher profiles are written under results/altirra-850/. Automated test profiles, transcripts, logs, screenshots, and JSON results live under the relevant results/ subdirectory documented in Testing And Evidence.