Sending 240 bytes in NUS nrf_connect_sdk

[Sunil vignesh]

Hi,

I am trying to send the max 240 bytes in NUS SERVICE nRF_CONNECT_SDK

I have seen the ble throughput example and changed

CONFIG_BT_RX_BUF_LEN=255

CONFIG_BT_CTLR_TX_BUFFER_SIZE=251
CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

error:

W: No ATT channel for MTU 90
W: No buffer available to send notification
W: No ATT channel for MTU 91
W: No buffer available to send notification
W: No ATT channel for MTU 90
W: No buffer available to send notification
W: No ATT channel for MTU 90
W: No buffer available to send notification
W: No ATT channel for MTU 91
W: No buffer available to send notification
W: No ATT channel for MTU 91
W: No buffer available to send notification
W: No ATT channel for MTU 90
W: No buffer available to send notification
W: No ATT channel for MTU 90
W: No buffer available to send notification
W: No ATT channel for MTU 9E: ***** MPU FAULT *****
E:   Stacking error (context area might be not valid)
E: r0/a1:  0xdf5f5e79  r1/a2:  0x9a650424  r2/a3:  0xe6fde46b
E: r3/a4:  0x6024e085 r12/ip:  0x49fb63e0 r14/lr:  0x11fd2a18
E:  xpsr:  0x21000000
E: Faulting instruction address (r15/pc): 0x00034ff0
E: >>> ZEPHYR FATAL ERROR 2: Stack overflow on CPU 0
E: Current thread: 0x20003118 (unknown)
E: Resetting system

[Sunil vignesh]

I have tried by setting MTU size as 250 in the mobile app

then i able to receive the > 20 bytes

But problem is every time in APP before sending the data i need to set the value

Instead of that i need to config in Project itself

How to config ATT_MTU_SIZE = 251

[Sigurd]

Hi,

Try to call bt_gatt_exchange_mtu() , e.g. as done here: https://github.com/nrfconnect/sdk-nrf/blob/v1.6.0/samples/bluetooth/central_uart/src/main.c#L366

[persimmon]

I run into exact same problem. How to call bt_gatt_exchange_mtu(). I am running a modified version of the peripheral_uart example.