Handle multiple requests one after each other

[mpiffari]

Hello folks and @dinesharjani - @philips77 - @roshanrajaratnam,
I'm struggling with the possibility of sending multiple requests one after each other without waiting for the response, and then receiving responses with matching sequence numbers.
Do you have more information about this? Is it still possibile, in order to speed up procedure? In my own implementation, it is nearly impossible to reach 8/9 kB7s as per NRC Connect dfu procedure or NRF Device manager (maybe with PRNs?).

Maybe, is it possible to know what happen in NRF Connect under the log "Uploading firmware"?

[philips77]

Hello,
I don't remember if that's supported in nRF Connect, but for sure nRF Connect Device Manager do support it.
On Android it only works on the "Basic" mode. In "Advanced", where you can do all the steps manually, each packet awaits a notification, as it's using the legacy uploader. On iOS both views use the same uploader.
NCS 2.0 added McuMgr Params request in OS Group, which returns number of buffers and the buffer size. Although it doens't have to work all the time, you should be able to use all but one buffer (which is used for sending responses?).
This feature works better when MTU is high (we use 498) and Data Length Extension (DLE) is high (251), so the bytes are sent faster than flash can save them. The only bottleneck becomes the flash, not OTA transfer.
Remember that each packet has to have a different SEQ number than any other packet that hasn't been acked yet.

[mpiffari]

Hi @philips77 ,
thanks for your comment.

Just two questions:

• How can I obtain such an high MTU? With a Write (and not a write without response)? Or I need to set some specific flag in config file on firmware side? (maybe CONFIG_NCS_SAMPLE_MCUMGR_BT_OTA_DFU_SPEEDUP?)
• DLE: is a feature that need to be enabled via config file?

[philips77]

Hello,
Sorry for the delay, I missed your questions.

How can I obtain such a high MTU? With a Write (and not a write without response)? Or I need to set some specific flag in config file on firmware side? (maybe CONFIG_NCS_SAMPLE_MCUMGR_BT_OTA_DFU_SPEEDUP?)

In nRF Connect SDK you need to set a KConfig option to set the MTU. This will allow sending Write Without Response packets of large size on the ATT layer.

For Write With Response the packet size is always at most 512 bytes, but this is sent using Prepare Write commands if MTU is not high enough. For uploading data it's better to use Write Without Response, just negotiate the MTU to be 498.

DLE: is a feature that need to be enabled via config file?

Yes, this is also enabled in the KConfig file. I think you use CONFIG_BT_CTLR_DATA_LENGTH_MAX for that, with max value of 251. This defines the max size of a packet on L2CAP layer. It this length is not enough to send large packet (MTU>DLE), then the ATT layer will automatically split longer packets.