Question regarding the transfer speed of the BLE on nrf52832 using nordic uart service

[Rajat]

Hi Everyone

I have been trying to send a text file(reading from SD card) , The size of the file is 2MB. 
I am using softdevice s132 for nrf52832 to transfer the text file via the Bluetooth to the Android application(nrf Connect). 
I am able to transmit the file to the nrf connect app , but the problem is that the transfer is too slow , it gives me an average speed of around 20KBPS , which is very less for our application.

What  i would like to know is 
1. Is there any specification of the softdevice which i should enable to receive the maximum throughput(or atleast 3/4th of it). 
2. Is it related to the service that i am using , I am using Nordic Uart Service. 

Here are the settings that i have been using
PHY - LE 1M for both Tx and Rx
Here is a log file , i am attaching , if that helps.

5001.Log 2020-10-07 12_34_02.txt

[Sigurd]

Hi,

We have some throughput numbers here: https://infocenter.nordicsemi.com/topic/sds_s132/SDS/s1xx/ble_data_throughput/ble_data_throughput.html

I assume you have NRF_SDH_BLE_GAP_DATA_LENGTH set to 251 in sdk_config.h

You might want to increase NRF_SDH_BLE_GAP_EVENT_LENGTH so that it matches the connection interval you are using.

It could be that the phone you are using does not support data length extension(DLE).

[Rajat]

Updates :

1. With the nrf Dongle connected to PC and data transfer via nrf Connect for PC gives me desirable result and following result are seen on connection

  Sending PHY Update, 2 Mbps.
  ATT MTU exchange completed. MTU set to 247 bytes.
  Data length updated to 251 bytes.
  PHY update accepted
  PHY set to 2 Mbps.


2. With any Android device and nrf Connect for android gives me the following results on connection(My android mobile is oneplus 7pro , it supports BLE5.0 with PHY-2M)

Sending PHY Update, 2 Mbps.
ATT MTU exchange completed. MTU set to 247 bytes.
Data length updated to 251 bytes.
PHY update rejected
PHY set to 1 Mbps.Connection interval updated: 0x6, 0x6.
ATT MTU exchange completed. MTU set to 247 bytes.
Connection interval updated: 0x24, 0x24.
Data length updated to 251 bytes.

Please help asap , it is very urgent for us to complete

[Sigurd]

Try increasing NRF_SDH_BLE_GAP_EVENT_LENGTH , e.g. to 50

[Rajat]

My connection interval is 7.5 ms by default , but when it connects to android nrf connect application , the PHY updates get rejected and the paramteres get modified 
But in the case of nrf dongle and pc nrf connect , no modifications in my original values occur and i get desirable results.

[Rajat]

It goes in a breakpoint if i change this value

[Rajat]

NRF_SDH_BLE_GAP_EVENT_LENGTH 50 , makes my software go to breakpoint

[Sigurd]

Rajat said:

NRF_SDH_BLE_GAP_EVENT_LENGTH 50 , makes my software go to breakpoint

You need to allocate more RAM to the SoftDevice, after increasing NRF_SDH_BLE_GAP_EVENT_LENGTH 

[Rajat]

Please explain the below mentioned behaviour as well , i think it is something related to the nrf Connect for android
Because , if i manually change the PHY from nrf connect , everything seems to work fine and at reasonable speeds

1. With the nrf Dongle connected to PC and data transfer via nrf Connect for PC gives me desirable result and following result are seen on connection

  Sending PHY Update, 2 Mbps.
  ATT MTU exchange completed. MTU set to 247 bytes.
  Data length updated to 251 bytes.
  PHY update accepted
  PHY set to 2 Mbps.


2. With any Android device and nrf Connect for android gives me the following results on connection(My android mobile is oneplus 7pro , it supports BLE5.0 with PHY-2M)

Sending PHY Update, 2 Mbps.
ATT MTU exchange completed. MTU set to 247 bytes.
Data length updated to 251 bytes.
PHY update rejected
PHY set to 1 Mbps.Connection interval updated: 0x6, 0x6.
ATT MTU exchange completed. MTU set to 247 bytes.
Connection interval updated: 0x24, 0x24.
Data length updated to 251 bytes.