Bluetooth Transport

Bluetooth Transport

The Glead ZYM-BI201 (TI CC2540) is connected directly to the F411. Rewair uses it as a transparent UART-to-GATT bridge. The physical pinout is documented in Hardware Architecture.

USART1 runs at 115200 8N1 and is dedicated to the BI201; WICED stdio is disabled. On startup Rewair resets the module, sends AT#RS, then selects transparent mode with AT#WM=0.

GATT service

Service UUID:

2f2dfff0-2e85-649d-3545-3586428f5da3

Direction	Characteristic	Operation
F411 → central	2f2dfff4-2e85-649d-3545-3586428f5da3	Notify
Central → F411	2f2dfff5-2e85-649d-3545-3586428f5da3	Write with response

The tested ATT MTU is 23, leaving 20 bytes per GATT value. GATT boundaries are stream chunks and do not align with Rewair frames.

Rewair frame

Protocol version 1 COBS-encodes each record, appends a little-endian CRC32, and uses 0x00 as the frame delimiter.

Field	Size	Notes
Version	1	1
Type	1	Request 1, response 2, event 3, ACK 4
Flags	1	FIRST=0x01, MORE=0x02
Operation	1	Stable API operation ID
Request ID	2	Little-endian
Sequence	2	Fragment number, starting at zero
Status	2	HTTP-compatible; zero in requests and ACKs
Payload length	2	At most 32 bytes
Payload	0–32	UTF-8 JSON bytes
CRC32	4	Header and payload

Complete requests are limited to 1024 bytes and responses to 2048 bytes.

The CC2540 bridge has no UART flow control. Rewair uses 32-byte logical fragments and stop-and-wait response delivery: the central ACKs each fragment with MORE, the F411 waits 150 ms before the next fragment, and an ACK times out after five seconds. The F411 also waits 200 ms before its first response so the incoming UART request can drain.

API exposure

The transport uses the shared rewair_api operation IDs:

ID	Operation	Bluetooth status
1	Capabilities	Enabled
2	Status	Enabled
3	Scan	Enabled
4	Saved networks	Enabled
5–12	Join, forget, priority, settings, time, display, reset, update	Locked

Capabilities reports "mutations":false. Bench testing showed that the BI201 service accepted connections and writes without an authorization prompt, so mutations remain disabled pending an authenticated Rewair session. OTA remains Wi-Fi-only.

Clients and diagnostics

The HTTPS-hosted UI provides the normal Web Bluetooth client; see Web UI and API. For protocol diagnostics on macOS:

uv run --with bleak==3.0.1 python \
  tools/bi201/ble_api_probe.py --read-all --quiet-frames

tools/bi201/ble_gatt_probe.py works below the framed API. The standalone wiced/apps/rewair/bi201_probe firmware and its build/flash/read scripts are retained for module-level UART and GATT investigation.