DFU from nRF Connect very slow when using nRF51 dongle

[jev]

I'm using nRF Connect v2.6.2 on windows 10 using an nRF51 dongle to update my target OTA. Target is an nRF52832, softdevice s132 v6,1,1. The DFU process takes like forever!

When using an nRF52840 dongle, DFU is much, much faster. Same when updating from an Android phone using nRF Connect; much faster then from the PC.

What is restricting the speed with this nRF51 dongle? Is there a restriction on MTU sizes, on speed or anything?

[Edvin]

Hello, 

You are correct. The nRF51 dongle uses the S130 softdevice, which doesn't support MTU larger than 23 bytes. This will lead to a significant reduction in link throughput, which is probably why you see the DFU update being much faster using either a phone or another device that supports MTU > 23 bytes. 

Best regards,

Edvin