Android：如何获取与 BLE 心率 GATT 服务的测量特性相关的时间戳？

Question

I'm doing as the guide says and all work perfectly fine. I can discover the heart rate service from the GATT server and then get all the updates from the heart rate characteristic samples.

However, is there a characteristic to get the timestamp related to each heart rate sample? Getting the System.currentMillis() whenever I get a sample seems too inaccurate to me. I'd want something like this

 if (UUID_HEART_RATE_TIMESTAMP.equals(characteristic.getUuid()))

EDIT: I'm referring to the example at the line

if (UUID_HEART_RATE_MEASUREMENT.equals(characteristic.getUuid())) {

where the app can parse the data received by the heart rate sensors. Is there a way to parse a timestamp value together with the heart rate? The result I need is something like a couple of values, not the single hear rate.

(timestamp, heart rate)

Answer 1

Receiving the exact timestamp related to a BLE heart rate measurement is impossible since this is not part of the BLE Heart Rate Service GATT specification :

3.4 Requirements for Time-Sensitive Data

The Heart Rate Measurement characteristic contains time sensitive data and is considered a time-sensitive characteristic, thus the following requirements apply:

Since this service does not provide for a time stamp to identify the measurement time (and age) of the data , the value of the Heart Rate Measurement characteristic shall be discarded if either the connection does not get established or if the notification is not successfully sent to the Client (eg, link loss).

As indicated by the documentation, you can assume that transmitted measurements are 'fresh' and therefore using the receiving device's timestamp upon arrival is a good approximation.

Unfortunately, RR-intervals might need more precision and are contained within the same not-timestamped measurements. Assessing the timestamp of individual RR-intervals might require some more trickery since multiple intervals are bundled together per measurement.

If more RR-Interval values are measured since the last notification than fit into one Heart Rate Measurement characteristic, then the remaining RR-Interval values should be included in the next available Heart Rate Measurement characteristic.

If there is no available space in the internal buffer of the Heart Rate Sensor, it may discard the oldest RR-Interval values.

You might thus have to use the transmission interval to assess whether or not measurements have been dropped, which impacts your ability to timestamp RR-intervals.

In typical applications, the Heart Rate Measurement characteristic is notified approximately 1 time per second and includes the Heart Rate Measurement Value field and, if supported, the RR-Interval field.