Need long battery life with fast connection interval

[Dawei]

We need fast response from peripheral to central. That means we need a fast connection interval. We are using less than 100mS. But that results in an unacceptable battery life. We are trying different strategies to address this problem. One idea is to have a longer connection interval after some period of non-use. But this takes several seconds to renegotiate the connection parameters. Anyone got some idea about this?  I would think this is a common problem that has a solution.

[mrono]

Dawei said:

So we are thinking about some scheme where maybe we can adjust the slave latency

Hmm.. Is there a way to tell the BLE stack to wake up on every interval even if you have a nonzero slave latency? Because as far as I know the only way to really adjust it is to renegotiate the connection parameters. And that undoes much of the benefits.

If your device also sends some data to the central, then one option is to send dummy notifications. So keep a large slave latency all the time. And when you do want to wake up on every interval, send a dummy notification to force the peripheral to wake up.

[Dawei]

I don't totally understand this. If the peripheral has a high latency, it won't be listening for data from the central. Am I wrong? I guess what we need is some way to force the peripheral to "override" the latency.

[mrono]

Yes, that's what I was trying to say.

I'm not sure if there is a way to tell the Nordic BLE stack that you would like it to listen on every interval even if you have negotiated a high slave latency.

But one way to override this is to have something to send from the peripheral to the central. So when you'd like to override the latency, send a dummy notification from the peripheral every 100ms. That forces the peripheral to listen.

This would mean some extra communication, but it would avoid the need to renegotiate.