not able to send more the 20 bytes using bt_gatt_notify api

RE: not able to send more the 20 bytes using bt_gatt_notify api

madhurubharath — Thu, 06 Mar 2025 12:16:08 GMT

thank you edvin after adding the below configuration it solved.

CONFIG_BT_BUF_ACL_RX_SIZE=251

CONFIG_BT_L2CAP_TX_MTU=247

CONFIG_BT_BUF_ACL_TX_SIZE=251

CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

make sure in nrf connect app also need to change the MTU size please enable the option in settings->connecting->autoupdate MTU TO 512

RE: not able to send more the 20 bytes using bt_gatt_notify api

Edvin — Fri, 03 Mar 2023 09:02:16 GMT

What NCS version are you using (since you are using Segger Embedded Studio)?

Looks like a toolchain issue. Try deleting and re-create your build configuration.

RE: not able to send more the 20 bytes using bt_gatt_notify api

Vivek — Fri, 03 Mar 2023 07:23:07 GMT

Hi, we tried this. There is error in compilation. some files shows missing

RE: not able to send more the 20 bytes using bt_gatt_notify api

Edvin — Fri, 07 Oct 2022 07:10:25 GMT

Did you test the application I attached in the previous reply? It requests a higher MTU from the peripheral application (so you don't need to do it from the central/mobile.

BR,

Edvin

RE: not able to send more the 20 bytes using bt_gatt_notify api

madhurubharath — Fri, 07 Oct 2022 04:54:46 GMT

hi edvin ,

now its working after changing the request MTU size in nrf connect app (mobile).

now i am able to receive up to 512 bytes in nrf connect app.

but if we use any other app it my don't have this option how can we handle in code.

warm regards,

bharath.m

RE: not able to send more the 20 bytes using bt_gatt_notify api

Edvin — Thu, 06 Oct 2022 11:27:40 GMT

Well. In that case, I guess the MTU is not updated.

Is bt_gatt_exchange_mtu() called? If so, what does it return?

Can you try the attached project? I was able to use an MTU of 247 using this, at least:

devzone.nordicsemi.com/.../6663.peripheral_5F00_uart.zip

(Written in NCS v2.1.0)

Best regards,

Edvin

RE: not able to send more the 20 bytes using bt_gatt_notify api

madhurubharath — Thu, 06 Oct 2022 07:21:15 GMT

After flashing the code application is crashing and not able to connect to peripheral. but if i remove this function (bt_gatt_exchange_mtu) its connecting .

its not printing any log because its crashing or resetting the BLE.

warm regards,

bharath.m

RE: not able to send more the 20 bytes using bt_gatt_notify api

Edvin — Fri, 30 Sep 2022 08:06:09 GMT

Does the application crash/reset? Or does it trigger a bt_disconnect()? The bluetooth stack never disconnects on it's own. What does the log say?

BR,

Edvin

RE: not able to send more the 20 bytes using bt_gatt_notify api

madhurubharath — Fri, 30 Sep 2022 04:58:31 GMT

its disconnecting the BLE. from central device.

RE: not able to send more the 20 bytes using bt_gatt_notify api

Edvin — Thu, 29 Sep 2022 13:42:49 GMT

[quote user="madhurubharath"]if i use bt_gatt_exchange function i ma not able to connect the device to central device[/quote]

What does it do? Does the log say anything? Does it print "MTU CHANGED" or "MTU NOT_CHANGED"?

[quote user="madhurubharath"]

and now i am using default_con in the place of NULL

tm_status=bt_gatt_notify(default_conn, &ccbg_serv.attrs[1], sPtr ,ble_tx_size);

[/quote]

What does bt_gatt_notify return? What is tm_status after bt_gatt_notify has been called? (try printing it in the log).

RE: not able to send more the 20 bytes using bt_gatt_notify api

madhurubharath — Wed, 28 Sep 2022 13:10:55 GMT

if i am trying to use this function bt_gatt_exchange_mtu this function is not fetching controller stops rest of the functions are not working.

it will be grate for my project if you solve this problem

thanks &regards,

bharath.m.

RE: not able to send more the 20 bytes using bt_gatt_notify api

madhurubharath — Wed, 28 Sep 2022 07:17:40 GMT

hello edvin if i use bt_gatt_exchange function i ma not able to connect the device to central device its i think it resting the controller i dont know exactly.

err = bt_gatt_exchange_mtu(default_conn,&exchange_params);
if(err == 0)
{
DPRINTF("MTU CHANGED\n\r");
}
else
{
DPRINTF("MTU NOT_CHANGED\n\r");
}

and now i am using default_con in the place of NULL

tm_status=bt_gatt_notify(default_conn, &ccbg_serv.attrs[1], sPtr ,ble_tx_size);

please help to solve this problem

regards,

bharath.m

RE: not able to send more the 20 bytes using bt_gatt_notify api

Edvin — Tue, 27 Sep 2022 11:47:50 GMT

Did you call bt_gatt_exchange_mtu(), like it is done in the throughput example found in ncs\nrf\samples\bluetooth\throughput?

And also, I see that you are using bt_gatt_notify(NULL, &ccbg_serv.attrs[1], sPtr ,ble_buff_len); that is, without the connection handle. Can you please try to use the connection handle instead of NULL when you are trying to send the data? I suspect that when you don't specify a specific connection, you can't use an MTU larger than the default MTU size. At least it is a quick check whether it works changing that.

Best regards,

Edvin

RE: not able to send more the 20 bytes using bt_gatt_notify api

madhurubharath — Tue, 27 Sep 2022 10:20:22 GMT

hello edvin,

thank you for quick response,

still i ma facing same issue with bt_gatt_notify API.

still am getting return type"-128" from "tm_status=bt_gatt_notify" if i send 20 bytes it successfully notifying the data. any other configuration need to change?

regards,

bharath

RE: not able to send more the 20 bytes using bt_gatt_notify api

madhurubharath — Tue, 27 Sep 2022 08:16:43 GMT

APP FILE:

uint8_t TM_u8SendData_central_dev(tm_u8_t *BT_rx_data,uint16_t rxbuflen)

{

int tm_status=0,Ack_len,nty_count=0,ble_tx_size=0;

ble_buff_len=rxbuflen;

uart_irq_rx_enable(uartDev);

char AckMent[11];

char buff_size[20];

if(tm_flag == 1)

{

size_t size=0, SendLen=0;

char *sPtr= BT_rx_data;

tm_status=bt_gatt_notify(NULL, &ccbg_serv.attrs[1], sPtr ,ble_buff_len);

if(tm_status == 0)

{

Ack_len = sprintf(AckMent,"{\"ack\":[0]}");

UARTQueueData(&AppInstance.UartQTx, uartDev,AckMent,Ack_len);

sprintf(buff_size,"pkt_data_size:%d",ble_buff_len);

UARTQueueData(&AppInstance.UartQTx, uartDev,buff_size,sizeof(buff_size));

return 0;

}

else

{

Ack_len = sprintf(AckMent,"{\"ack\":[-1]}");

UARTQueueData(&AppInstance.UartQTx, uartDev,AckMent,Ack_len);

sprintf(buff_size,"pkt_data_size:%d",ble_buff_len);

UARTQueueData(&AppInstance.UartQTx, uartDev,buff_size,sizeof(buff_size));

return -1;

}

prj.config:

CONFIG_BT_BUF_ACL_RX_SIZE=251

CONFIG_BT_L2CAP_TX_MTU=247

CONFIG_BT_BUF_ACL_TX_SIZE=251

CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

this is my configuration code:

if i transmitt more then 20 bytes its returning -1

please help me to solve this issue

regards,

bharath.m

RE: not able to send more the 20 bytes using bt_gatt_notify api

Edvin — Mon, 26 Sep 2022 12:57:18 GMT

Hello,

We usually refer to our throughput sample found in ncs\nrf\samples\bluetooth\throughput. However, there are a lot of configs from the prj.conf file in that sample.

[quote user="madhurubharath"]please suggest any other method to transmit data[/quote]

You still want to use that API, but you want to ensure that you actually have a higher MTU. Please check this ticket for more info on how to increase the MTU size in a connection.

Best regards,

Edvin

RE: not able to send more the 20 bytes using bt_gatt_notify api

madhurubharath — Mon, 26 Sep 2022 10:29:32 GMT

please suggest any other method to transmit data.