Why can't I set the size of each frame when downloading data in my application?

[duxinglang]

I am using the 9160 to develop a product for the customer. Its sdk version is ncs1.9.0, and the firmware version of the modem is v1.3.1. The device needs to download data from the background at some time. At present, the default size of data per frame is 2048 bytes. To speed up the download, I want to change the size of data per frame to 4096, but it is strange.

Although I have set the macro of CONFIG_DOWNLOAD_CLIENT_HTTP_FRAG_SIZE_4096 in the prj.conf file, but in the autoconf. h generated after compilation, I found that CONFIG_ DOWNLOAD_CLIENT_HTTP_FRAG_SIZE is still defined as 2048. Why does my setting not work?

[Håkon Alseth]

Hi,

 

Selecting a higher fragmentation size will highly likely not help your overall speed.

What speed are you currently seeing?

Are you using NB-IoT or LTE M1?

 

Kind regards,

Håkon

[duxinglang]

Hi!

I now use the NB-iot network. A 4096 byte frame data can be written to flash more easily, because one sector of flash is also 4096 in size. In this way, each frame data is written to each sector. That will reduce many unnecessary operations, such as sector erasure. In fact, when my device is running in ncs1.2.0, the size of each frame of data it downloads is 4096. I don't know why this value cannot be set when running in ncs1.9.0.

[Håkon Alseth]

Hi,

 

Yes, it is not possible to select 4096 fragment size anymore.

This is due to the modem tls stack not being able to handle fragments >2048 bytes, the download_client has imposed a limitation in kconfig:

https://github.com/nrfconnect/sdk-nrf/blob/v1.9.0/subsys/net/lib/download_client/Kconfig#L42-L45

 

For unsecure sockets, the modem can handle up to 4096 bytes.

 

I would recommend that you read in 2k chunks instead.

 

Kind regards,

Håkon