RTI AD-4x / AD-8x (HTTP)

GEM driver rti_ad8x_http controls an RTI AD-4x / AD-8x multi-zone audio distribution amplifier over the local HTTP control interface (rti_*.cgi) served at port 80.

Functionally equivalent to the rti_ad8 TCP driver — pick this one where the TCP control port becomes unresponsive after extended uptime. The web UI keeps responding on units where the TCP socket has wedged.

What it does

• Per-zone power, mute, volume, and source select via GET requests to rti_zp0/zp1.cgi, rti_zm0/zm1.cgi, rti_zvs.cgi, rti_zi.cgi.
• Periodic poll of rti_status.cgi to reconcile state — the amp does not push updates.
• Optimistic state push on each command so the UI updates without waiting for the next poll.
• Transparent re-login when the amp serves the login page in place of a CGI response (silent session expiry).

Prerequisites

• AD-4x or AD-8x amplifier on the LAN with HTTP control enabled (port 80 by default).
• Web-UI password — the one set on the amp's rti.shtml login page. Leave the GEM attribute blank to use the factory default (rti).

Setup steps

1. Confirm http://<amp-ip>/rti.shtml loads the RTI login page.
2. Create the device with driver rti_ad8x_http, enter the IP, and set the web-UI password.
3. Add a GEM Zone for each amplifier output. Set zone.address to 1..4 (AD-4x) or 1..8 (AD-8x) — this is the value the amp expects in the z= query parameter.
4. On connect, the driver logs in, polls rti_status.cgi, and refreshes every status_interval ms (default 5000).

Attribute reference

Device

Name	Required	Description
ip	yes	LAN IP of the amplifier.
password	no	Web-UI password. Sent to /rti_login.cgi?pw=… on each session. Defaults to rti. Stored as a secure attribute.
port	no	HTTP port. Defaults to 80.
status_interval	no	Poll interval (ms) for rti_status.cgi. Defaults to 5000.
volume_min	no	Soft floor on GEM volume (0..100). Requests below this are clamped before being sent. Defaults to 0 (no floor).
volume_max	no	Soft ceiling on GEM volume (0..100). Useful for capping how loud a zone can be driven. Defaults to 100 (no cap).
debug_log_status	no	When true, dumps the first status response body per connect to the log for parser tuning.

Zone

No required zone attributes. Set zone.address to the 1-based output number.

Commands

Name	Args	Notes
zone_on / zone_off	address	Powers the zone on or off.
mute_on / mute_off	address	Mute control.
volume	address, volume	Volume 0-100 in GEM units; converted to wire dB internally.
volume_up / volume_down	address	±5 GEM units from the cached current value.
set_input	address, input	Route a physical amp input (1-based) to a zone. Writes the value to zone.input. Implicitly powers the zone on.
all_zones_on / all_zones_off	—	Power all zones (sequential fan-out, one HTTP request per zone).
mute_all / unmute_all	—	Mute / unmute all zones (sequential fan-out).
request_status	—	Trigger an immediate status poll.
passthrough	path	Send a raw GET to the amp. path is the URI after the host, e.g. rti_zp1.cgi?z=1.

Volume scale

GEM exposes 0..100; the wire is dB attenuation -78..0 (0 = loudest, -78 = quietest). The driver converts in both directions. The rti_status.cgi body reports volume as an unsigned attenuation (e.g. "vol":"56" = -56 dB); the driver inverts the sign before mapping to GEM units.

Use volume_min / volume_max to cap or floor the GEM-side range — these are soft caps on the write path only, so a value set above the cap from the front panel still surfaces accurately on the next status poll.

Known limitations

• The amp does not push state — all reads happen via the polling interval. Lower status_interval for tighter UI sync at the cost of more LAN traffic.
• rti_status.cgi returns near-JSON with SSI comments inlined ({"zone": <!--#zn1-->{...}}). The driver strips comments before parsing and infers zone numbers from the array index, since the JSON itself does not carry them.
• Sessions are held by client IP — no cookie is set by most firmware. The driver re-logs in transparently when the amp serves the login page back in place of a CGI response.
• Success and failure both return HTTP 200. The driver disambiguates on body content (<!-- ok --> for success, an HTML Parameter Error page for failure).
• set_input implicitly powers the target zone on — observed on AD-8x firmware. Setting a source on a powered-off zone will show pwr=1 on the next status poll.

:::info zone.input vs zone.source The driver writes the amp's physical input number (1..N) to zone.input. It never writes zone.source — that attribute is reserved for GEM's av_source foreign key and is owned by the AV-routing macros. Writing the raw amp input into zone.source would be rejected by the av-source-change handler as an invalid av source. :::

Troubleshooting

Symptom	Check
Login fails / status returns HTML.	Confirm the password attribute matches the rti.shtml web UI password exactly. The driver re-logs in on 401/403 but a wrong password will loop.
Volume slider feels backwards or compressed.	Older firmware uses a -62..0 range instead of -79..0. The driver assumes the newer range; expect proportionally lower GEM volume on legacy firmware.
Zone state diverges from the web UI.	Lower status_interval; the amp does not push state, GEM only sees changes after the next poll.
Commands rejected with parameter error.	Confirm zone.address is the 1-based output number (1-4 on AD-4x, 1-8 on AD-8x), not a padded string.

:::tip TCP vs HTTP If the existing rti_ad8 TCP driver works reliably for you, stick with it — TCP is lower-overhead. Switch to rti_ad8x_http if you see the amp's TCP control port stop responding after weeks of uptime while the web UI continues to work. :::