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Record Bluetooth/WiFi findings and Phase 1 status in the plan

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Checked against the pinned Circle tree after the question of supporting
Bluetooth and WiFi on the Pi alongside USB.

Bluetooth is not possible on Circle, for two independent reasons: the stack
was removed for legal reasons and was classic Bluetooth in any case, with no
BLE or GATT anywhere in the tree, while MIDI over BLE is GATT; and the
remaining HCI transport would need a USB dongle in host mode, which the
gadget-only constraint already rules out.

That costs nothing. The WU-BT10 does GATT MIDI to the PC, and the PC is the
hub, so Bluetooth MIDI works today with no firmware change - it just
terminates one hop earlier. Section 3 now describes it that way rather than
as a spare part.

WiFi is possible via addon/wlan but is a project rather than a flag: Circle
lists WLAN as unknown on the Zero 2 W, ships no RTP-MIDI (only mDNS
advertisement of _apple-midi._udp), needs firmware blobs off the card at
boot, and its coexistence with gadget mode is unproven. Deferred, not
rejected; that last point is what to settle first.

Also marks Phase 1 done-but-unverified, and records that Phase 0 should bench
rpi_ws281x in SPI mode on GPIO10, since the stock examples use GPIO18 over
PWM and would prove the wrong wiring.

Claude-Session: https://claude.ai/code/session_01TVCB25LBsmeteWvaSMz4Ne
This commit is contained in:
prosolis
2026-08-27 22:19:18 -07:00
parent 3904703de1
commit 6a59766b79
1 changed files with 67 additions and 4 deletions
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PIANO-LED-CIRCLE-PLAN.md
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@@ -84,8 +84,11 @@ close off "plug the piano into the Pi" as a fallback.
**Casio WU-BT10**
- Bluetooth 5.0. Profiles: **A2DP (audio)** and **GATT (MIDI over BLE)**. Codec SBC.
- USB bus powered, 0.25W, no separate supply.
- Not used in this build's MIDI path. Freed up for streaming audio from the PC to the
piano's own speakers over A2DP, if wanted.
- **This is the project's Bluetooth MIDI path**, and it terminates at the PC, not the
Pi. Piano -> WU-BT10 -> PC over BLE GATT, then PC -> Pi over USB as usual. See
section 3a for why it cannot terminate at the Pi.
- A2DP is also available for streaming audio from the PC to the piano's own speakers,
if wanted.
- Source: https://support.casio.com/en/support/answer.php?cid=008006001002&qid=104463&num=1
**Reference build** (https://yanniznik.com/building-a-led-piano-visualizer/)
@@ -95,6 +98,53 @@ close off "plug the piano into the Pi" as a fallback.
- ~$75-100 total. Includes a $30 iConnectivity mio MIDI interface **we do not need**,
because the PX-S7000 has USB-B.
## 3a. Bluetooth and WiFi on Circle
Checked against the pinned Circle tree (Step51) on 2026-08-27, after the question was
raised of supporting Bluetooth and WiFi on the Pi alongside USB.
**Bluetooth: not possible on Circle. Two independent blockers.**
VERIFIED: Circle's CHANGELOG states *"As announced the Bluetooth support has been
removed for legal reasons."* What remains, `lib/usb/usbbluetooth.cpp`, is a bare HCI
transport for a USB dongle with no stack above it. There is no BLE and no GATT
anywhere in the tree, and the removed stack was classic Bluetooth in any case. MIDI
over BLE *is* GATT, so even the deleted code would not have served.
VERIFIED: that transport would need a dongle in USB **host** mode, and Circle is
host-or-gadget and never both (see section 2). The Pi is a gadget here.
The consequence is not a loss. The WU-BT10 already does GATT MIDI to the PC, and the
PC is the hub, so Bluetooth MIDI is available today with no firmware change at all.
It simply terminates one hop earlier than the question assumed.
**WiFi: possible, but it is a project, not a flag.**
VERIFIED: `addon/wlan` is a Plan 9 derived BCM4343 driver (under its own Plan 9
license), usable with Circle's TCP/IP stack and a bundled WPA supplicant.
Four costs, all VERIFIED unless marked:
1. Circle's README lists the Raspberry Pi Zero 2 W as *"WLAN unknown for new
revision"*. The Zero W is Tested. That is the opposite way round from the BOM's
preference in section 5.
2. Circle ships mDNS advertisement for `_apple-midi._udp` but **not** the RTP-MIDI
protocol itself. The session layer would have to be written, or ported from
MiniDexed, which implements exactly this on Circle.
3. WLAN loads firmware blobs from `RPi-Distro/firmware-nonfree` off the SD card at
boot, which reintroduces filesystem reads and weakens the power-cycle-safe
property that section 2 was built around.
4. ASSUMED: that WLAN coexists with USB gadget mode. WLAN is SDIO and so it probably
does, but both `addon/wlan` samples pair it with USB *host*, so this is unproven
and would need a spike before anything is committed to.
And it reintroduces exactly the LAN attack surface that section 2 names as the
deciding factor for this architecture.
**Decision (2026-08-27): USB first.** Bluetooth is taken on the PC side via the
WU-BT10, at no cost. WiFi is deferred, not rejected; if it is revisited, cost 4 above
is the first thing to settle, because it may close the option outright.
## 4. Assumptions to verify before spending money
1. **PX-S7000 is class-compliant USB MIDI.** Almost certainly true for a 2022
@@ -193,7 +243,10 @@ Throw all of this away afterwards. It never gets mounted, never gets a hostname,
never sits on the LAN permanently.
1. Piano to PC over USB-B. Confirm it appears in `aconnect -l`.
2. Pi Zero on Raspberry Pi OS, `rpi_ws281x`, Python REPL.
2. Pi Zero on Raspberry Pi OS, `rpi_ws281x`, Python REPL. **Configure it for SPI, so
the data line is GPIO10 (physical pin 19).** The stock `rpi_ws281x` examples drive
the strip from GPIO18 over PWM, but the Circle firmware uses SPI on GPIO10. Bench
on the default pin and the wiring you prove is not the wiring you keep.
3. Confirm: pixel 0 is at the end you think it is; `(note-21)*2` lights the right key;
the far end holds voltage under load; the colors look right *through the diffuser*,
which is not the same as how they look bare.
@@ -203,7 +256,17 @@ never sits on the LAN permanently.
Exit criteria: you know the hardware is good and you know exactly what you want the
firmware to do.
### Phase 1 - Circle firmware
### Phase 1 - Circle firmware [DONE 2026-08-27, unverified on hardware]
Written and building; see `firmware/` and README.md. Both kernel images build clean
against Circle Step51. Steps 2 and 3 were resolved by reading the Circle sources
rather than by trial: the WS28XX driver clocks the strip over SPI, putting data on
MOSI = GPIO10 = physical pin 19, and the gadget lifecycle follows
`sample/29-miniorgan`, which already carries a `USB_GADGET_MODE` path.
Nothing here has touched a real LED or enumerated on a real PC. The riskiest untested
part is USB enumeration, and it is blocked by section 10 along with all of Phase 0.
1. Clone Circle, pin the release, build a stock sample for the Zero to confirm the
toolchain and the boot path.