nRF Mcp Dfu freezes when »Number of packets« is set greater than about 356 packets

[John Miller]

Hey there,

today I'd tested around with the Dfu service.

• Peripheral is nRF51822 running Sdk 5.2.0 bootloader example (Softdevice 6)
• Central is Android 4.3 running nRF Mcp 1.9.1
• Testfile (nRF51822 Application) is Hrs Example (about 43k binary size)

In the settings of Mcp I found some Dfu options and I determined that the »Number of packets« value has an affect to the update data throughput.

My Android device connects with 48,75 ms connection intervall and transferes mostly about 4 packets at each connection intervall. So, the max throughput is theoreticly at

4 x 20 Byte / 48,75 ms = about 1.641 Byte/s

But when metering the Dfu throughput, I got just about 1.000 Byte/s. Well, after changing »Number of packets« from 20 to 300, I got about 1.600 Byte/s - nice.

But then, when I set »Number of packets« to greater values (e.g. to 400), the Dfu upload freezes at 16 % - and the same when I switching off the option »Packets receipt notification procedure«.

For »Number of packets«, I determined a treshold value of 356. This means that Dfu works with values up to 356, but for greater values the Dfu freezes at 16 %.

Ok, I don't expect higher throughput with higher »Number of packets« values. I'd just detected that issue and would report it.

Btw: Is this the right place for that kind of topics or should I rather put that in an issue tracker?

[David Edwin]

I second Aleksander here. This is a limitation of the Android(till 4.4.2) and iOS (checked till iOS 7)ecosystem at this point. When using Write commands to send data from the Central to the Peripheral, the app is not aware of the point when the write command is actually sent over the air.

The api used to call the write command on iOS and Android does not provide any method to the app to see if the internal queue is full. This results in the app hanging/stalling when the internal queue is full.

The Packets receipt notification procedure« was introduced to provide feedback to the app on the number of packets sent over the air successfully to the peer. You must set this to a value below the internal queue's maximum level.

So setting this to large values (greater than the internal queue max) or disabling this notification are likely to result in a stalled app on the phone.