PMD Control Point Commands

This is the command-level reference for the PMD control point once you already know the service layout.

The PMD Control Point characteristic (FB005C81-...) accepts write requests and returns responses via indications. Each command starts with an operation byte followed by a measurement type and optional parameters.

Operation Codes

Op Code	Name	Direction
`0x01`	Get Settings	Write → Indicate
`0x02`	Start Measurement	Write → Indicate
`0x03`	Stop Measurement	Write → Indicate

Get Settings Request

Queries the device for available settings (sample rates, ranges, resolutions) for a given measurement type.

[0x01] [measurement_type]

Example: query ECG settings → 0x01 0x00

Get Settings Response

The response indication begins with:

[0xF0] [op_code] [measurement_type] [error_code] [settings_data...]

0xF0 = response marker
error_code = 0x00 for success
Settings data is a sequence of TLV (type-length-value) entries:
- Type byte: identifies the setting (e.g., 0x00 = sample rate, 0x01 = resolution, 0x02 = range)
- Length byte: number of value bytes
- Value bytes: little-endian encoded setting values

Some firmware versions insert the settings payload starting at byte offset 4, others at offset 5. Our parser tries both offsets to handle this variation.

Start Measurement Request

[0x02] [measurement_type] [setting_tlv_1] [setting_tlv_2] ...

Each setting TLV follows the same type-length-value format as the response.

ECG Start

Typical parameters for ECG at 130 Hz, 14-bit resolution:

0x02 0x00
  0x00 0x01 0x82 0x00    // sample rate = 130
  0x01 0x01 0x0E 0x00    // resolution = 14

ACC Start

Typical parameters for accelerometer at 25 Hz, 16-bit resolution, 2 G range. Note the range TLV appears before the sample rate for ACC:

0x02 0x02
  0x02 0x01 0x02 0x00    // range = 2 (G)
  0x00 0x01 0x19 0x00    // sample rate = 25
  0x01 0x01 0x10 0x00    // resolution = 16

Stop Measurement Request

[0x03] [measurement_type]

Error Handling

If error_code in the response is nonzero, the command failed. Common causes:

Feature not supported on the current firmware
Invalid parameter combination
Stream already active

MTU Considerations

PMD data frames, especially ECG at 130 Hz, can exceed the default 23-byte ATT MTU. Request a larger MTU (our implementation tries 232, then falls back through ordered candidates) before starting high-rate streams. If the negotiated MTU is too small, frames will be truncated and decoding will fail.