BackBlind

Software project for controlling the Blinds in the Back of the house.

First steps

• Working pheriphals;
• Working BLE connection (easy to test with phone);
• Encoder + Button
• Motor control
• I2C
• Light sensor
• BME

Next steps

• Change to Zigbee
• Add to HA OTA updates (Zigbee)

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The firmware can be updated over Zigbee with the standard OTA Upgrade cluster (client on endpoint 1). Flash layout, see Core/Inc/ota_layout.h:

Address	Size	Content
0x08000000	16 KB	Bootloader (Bootloader/)
0x08004000	212 KB	Application
0x08039000	212 KB	Download slot
0x0806E000	4 KB	Update record
0x08070000	64 KB	Zigbee NVM (kept, device stays paired)

How it works:

1. The device finds the OTA server on the coordinator and asks for a new image at startup and once a day. A "check for update" from the server (Image Notify) also starts a query.
2. The image is downloaded into the download slot, then the CRC is checked and an update record is written.
3. After the server says to upgrade, the device reboots. The bootloader checks the image again, copies it to the application slot, and starts it.

First time (wired)

Devices running the old firmware (app at 0x08000000) must be flashed once over SWD:

• build/<preset>/Bootloader/Bootloader.hex (at 0x08000000)
• the application as usual (debugger / BackBlind.elf, now linked at 0x08004000)

The debugger only flashes the application, so the bootloader stays in place.

Releasing an update

1. Increase FW_VERSION in CMakeLists.txt.
2. Build. This creates build/<preset>/BackBlind-<version>.ota (manufacturer 0x1041, image type 0x0002) using tools/make_ota.py.
3. Offer the .ota file through the OTA server. For zigbee2mqtt use a local OTA index (ota: zigbee_ota_override_index_location). The device definition (external converter) must have OTA enabled.

Notes:

• If STM32CubeMX regenerates the linker scripts, set FLASH back to ORIGIN = 0x08004000, LENGTH = 212K. make_ota.py refuses images that are not linked for the app slot.
• Only the M4 application is updated. The CPU2 wireless stack is not.

Zigbee interface

Endpoint	Device	Clusters
1	Window covering	Basic, Identify, Window Covering (0x0102), BackBlind settings (0xFC10), OTA client
2	Simple sensor	Identify, Temperature, Humidity, Pressure, Illuminance

Window Covering (standard): tilt only blind. CurrentPositionTiltPercentage (0% = open, 100% = closed), Up/Open goes to OpenLevel, Down/Close to 100%, Stop, Go To Tilt Percentage. Mode bit 0 (reversed) inverts the motor direction.

BackBlind settings cluster 0xFC10 (manufacturer specific, plain integers):

Attr	Name	Type	Description
0x0000	TiltRange	uint16	Encoder steps from 0% to 100% (default 944)
0x0001	DeadSteps	uint16	Encoder steps of gear play on a direction change
0x0002	OpenLevel	uint8	Tilt (%) for the Up/Open command (default 50)
0x0003	StartupLevel	uint8	Tilt (%) assumed after a power loss
0x0004	SyncLevel	uint8	Write: the blind is now at x% (no movement)

The settings are stored in their own EE words and survive re-pairing.

zigbee2mqtt: copy zigbee2mqtt/backblind.mjs to <z2m data>/external_converters/.