CHG-0013: The Turntable Driver

Summary

The agent Pi gains a third driver, which listens to the amplifier’s tape output through a USB audio interface and reports the record that is playing.

After this change a record on the platter is a source on the now-playing bus beside iTunes, and the stand follows it.

Goal

• The agent runs itunes and turntable, and both are online.
• A record playing is reported as playing with its artist and title within about half a minute, and stopped about twenty seconds after the needle lifts.
• nowplayd gives it an album and a cover, and the stand lights from it.
• iTunes is followed as before.

Scope

In scope: three topics added to the np-relay account’s publish; the agent, its unit and its tools on the Pi; the recognizer and its Python environment on the Pi; NP_TURNTABLE_DEVICE and NP_DRIVERS in the Pi’s settings.

Out of scope: nowplayd, lightd, the stand, the console’s subscriptions (all already cover any source). A new image is built from the same files but no card is flashed. The Roland UA-4FX and its cable are already in place.

Risk and impact

Procedure

# 1. The grant. Expect one in-place update to the np-relay account.
cd infra/deevnet-tenant-eds && make plan && make apply

# 2. The agent, its unit and the recogniser. iTunes only, still.
make -C deploy/relay push
make -C deploy/relay status

# 3. Which input, and then the driver.
make -C deploy/relay turntable DEVICE=plughw:UA4FX
make -C deploy/relay drivers DRIVERS=itunes,turntable

Verification

• make plan shows the account updated in place, with three topics added.
• After push: the agent is active, and iTunes is online on the console.
• After drivers: make -C deploy/relay status shows the turntable’s input, its recognizer and the endpoint all ok.
• With a record playing, eds/nowplaying/source/turntable/state is playing with an artist and a title, and eds/nowplaying/current has an album and art.
• The stand changes to the record’s colors.
• With the needle lifted, the source is stopped within half a minute.
• With the interface unplugged, the source is offline and iTunes carries on.

Undo

make -C deploy/relay drivers DRIVERS=itunes

That stops the listening and every request to the recognizer. The grant, the recognizer and the unit can stay as they are; the unit is put back by pushing from the commit before this one.

Outcome

| about 03:40 | make apply, by the owner. The account reads back with the three turntable topics granted, and the same password. | | 03:41 | make drivers DRIVERS=itunes,turntable, by the owner. The agent started both drivers, and fourteen seconds later reported playing on the turntable: Phil Collins - It Don't Matter to Me. | | 03:42 | The same target run a second time, from the session making this change, which had not been told it was done. It removed the NP_DRIVERS line and did not put it back; the agent restarted with the unit’s default, itunes,spotify. Spotify was polled for 38 seconds and the turntable was not listened to. | | 03:43 | The line put back by hand. The agent started itunes,turntable; the track was named again fourteen seconds later. Spotify reads as offline. | | 03:44 | The target mended (below) and run twice running: NP_DRIVERS=itunes,turntable both times. | | 03:45 | On the console: current is the turntable’s track, playing, with an album and a cover nowplayd found in the iTunes catalog, and lit_cover is that cover, so lightd has sent a scene from it. lp-stand-01 was offline, so the stand itself was not seen to change. | | 03:45 | The stand back online. It reported the scene for the record’s cover as applied: chase, four colors. | | 03:45:33 | The needle lifted, by the owner. The turntable reported stopped, about twenty seconds after. | | 03:45 | current then passed to iTunes, which was paused on another album, and the stand was lit from that album’s cover. See the follow-ups. | | 03:48:05 | The interface unplugged, by the owner. The turntable went offline, said once; iTunes stayed online and the agent stayed up. eds-agent-status failed on the missing input, by name. | | 03:49:08 | Plugged back in. The driver found it again by itself and went online, with no restart. | | 03:49 | Two faults seen in that, and mended: eds-agent-status went on failing after the input was back, and the reason logged for losing it was cut short. Pushed again; the status check passes with both drivers. |

Every goal was seen: both drivers online, a record named within half a minute and stopped twenty seconds after the needle lifted, an album and a cover from nowplayd, the stand lit from it, and iTunes followed throughout.

Departures from the plan

• The grant was planned and not applied before the Pi was changed: the session making this change was not permitted to run terraform apply. The steps that do not depend on the grant went ahead, and the driver stays off until it is applied, since a publish to a topic not granted is dropped in silence.
• The drivers target lost the setting when run twice. It deleted the line and appended the new one in one sed script, d and then $a on the last line. Its first run leaves the line last; on the second, the line deleted is the last line, and the append never happens. It has been in the target since CHG-0011 and nobody had run it twice. The two steps are now two commands, in drivers and in the new turntable target, which had copied it.
• Two faults found by pulling the cable. eds-agent-status looked for the last line about the turntable’s troubles and took no notice of it coming back online, so it failed for ever after one lost input. And the driver read what arecord said on its way out before arecord had finished saying it, so the reason logged ended at pcm_read:2221:. Both are mended and pushed. The second has not been seen with a cable pulled since: the fix is to wait for arecord to exit before reading what it said.
• The confinement was tried with systemd-run before the driver is turned on, which the plan did not have. It is the one part that could not be tested on a desk.

Follow-ups

• Lifting the needle lights the stand from whatever iTunes has paused. A paused source outranks a stopped one (ADR-0008), so when the record stops, a track paused in iTunes hours ago becomes current and the room is repainted for it. Nothing here is broken; whether a record ending should do that is a question for the arbiter, and a decision.

• The evidence ADR-0021 waits on.

• The image built for the Pi starts itunes,spotify unless a card says otherwise; a card for this Pi is written with DRIVERS=itunes,turntable TURNTABLE_DEVICE=plughw:UA4FX.

• The owner’s Discogs collection as a catalog in nowplayd, so the cover is the pressing on the platter: a decision of its own.

• A local index of the owner’s records, so the recognizer is not needed: a decision of its own.