Extremely slow DFU over UART

[Igor]

We try to implement DFU over UART. The Mesh DFU example has been taken as a reference.
DFU is successful, but it takes about 1 hour (sic!) to transfer DFU ZIP package of size 123 KB.
Why is it so slow? How to make it normal speed?

[Mesh SDK 2.1.1, Nrf SDK 15.0, S140 6.1; 115200 bps, HWFC]

[bjorn-spockeli]

Hi Igor, 

are you talking about the serial transfer of the DFU image or the BLE transfer to the rest of the mesh devices?

Best regards

Bjørn 

[Igor]

I am talking about transfer of DFU image from PC to a "gateway" nRF device over UART.

nrfutil dfu serial -pkg dfu_prov-1.zip -p COM16 -b 115200 -fc --mesh

How can this command take 1 hour to execute?!

Edit

nrfutil dfu serial -pkg dfu_prov-1.zip -p COM16 -b 115200 -i 200 -fc -m

This reduces time from 68 min to 27 min. But this is still VERY slow just to copy 123 KB over serial. Why?

[bjorn-spockeli]

HI Igor, I am not able to reproduce the behavior you're seeing. Are you able to capture a logic trace of the UART pins? Have you tried reducing the interval(--i) below 200ms?

[Igor]

Results of tests with lower interval:

-i	time [minutes]
500	68
200	27
100	14
50	8.0
25	4.8
10	2.9
5	2.2
2	1.8
1	1.7

I am wondering, what is the smallest safe interval value? Documentation states that it is 200, however I did not notice problems with lower values.

bjorn-spockeli I can provide time-labeled hex capture of serial port flow or 2-channel scope image.

[bjorn-spockeli]

Hi Igor, 

The device connected to the pc will start forwarding the image to rest of the mesh network from the first packet received over the serial interface. It does not receive the entire image and then starts to forward the image piece by piece.

So as I understand, the serial interface will work with very low values, but the mesh network will get saturated and many devices on the network will miss DFU packets if the --i value is set to low.

The recommendation of 200 ms is from the point of view of the network and not the single device. DFU is slow because it uses a trickle algorithm to ensure that everyone gets the packet. 

Best regards

Bjørn

[Igor]

So, that means that a firmware update puts whole system down for half an hour? Or the mesh network still works during firmware distribution?

I know that DFU works in side-by-side mode, but is there enough free bandwidth during DFU, so that is mesh network still able to transmit "useful" messages?

[bjorn-spockeli]

No, the mesh network is still operational during the side-by-side DFU since the trickle algorithm is used, i.e. the mesh can still send useful information during DFU in addition to the DFU packages. This is ofcourse given that the recommended --i value is used.