slave latency question

[HJLee]

I made all of the functions using nrf52832, s132.
Now I want to reduce the current consumption.

So, I tried changing the slave latency.
It was confirmed that the current consumption was reduced by increasing the slave latency.
However, the data reception of the master (mobile app) was slowed a lot.

Isn't slave latency reducing dummy data exchange?
It seems that there shouldn't be any impact on valid data exchange.

Why is data reception slow?
Am I wrong about slave latency?

[Hung Bui]

Hi HJLee, 

Using the slave latency shouldn't slow down data exchange. In theory when it's required to send data it should not skip the connection event (slave latency). So some thing must be wrong.

We may need ot look into how you queue and transfer your data. Please make sure you queue your data as much as possible (until the buffer is full) so that the softdevice knows there will be more data to send instead of going to sleep (and skip the connection event). 

You may want to take a sniffer trace of the communication so we can inspect what happens over the air. 

[HJLee]

Thank you for your answer.

When I use nRF Sniffer, it seems to be stopped as much as the slave lataency when master -> slave.
Unfortunately, I don't know much about the ble code.
As you said, how to increase the ble queue so the softdevice doesn't fall asleep?
Which parts of the code need to be modified?

[Hung Bui]

Hi, 

Seems that you are using write request from central to send data to the peripheral. 

This will be affected by Slave Latency, it's because the slave wouldn't know when the central needs to send data and may skip the connection event when the central wants to send data. 

Please note that if you want high throughput it's better to use write without response (write command) instead of write request. 

If you have to send data from central to peripheral, I think the best way to reduce power consumption is to control the connection interval. Meaning when you don't have data to transfer, you can configure the connection interval to a long one, for example once a second. And when you have lots of data to transfer you can configure the connection interval to shorter one, says 20ms. 

You can also increase the data length so that you can transfer more data in one single packet.