ncs 2.0.0 Bluetooth Peripheral_uart: cannot send long data stream

[BradEA]

Based on the Sample "Bluetooth Peripheral_uart:

My latest attempt to send long data stream:

I send:

1234567890123456789012345678901234567890123456789012345678901234567890\r

80 characters + '\r'

The tablet (nRF Connect) gets:

1234567890123456789012345678901234567890\r

and this shows up on the terminal:

[00:04:16.589,721] <wrn> bt_att: No ATT channel for MTU 74
[00:04:16.589,752] <wrn> bt_gatt: No buffer available to send notification
[00:04:16.589,843] <wrn> peripheral_uart: Failed to send data over BLE connection

What is going on?

My prj.conf:

#
# Copyright (c) 2018 Nordic Semiconductor
#
# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
#

# Enable the UART driver
CONFIG_UART_ASYNC_API=y
#CONFIG_UART_INTERRUPT_DRIVEN=y
CONFIG_NRFX_UARTE0=y
CONFIG_SERIAL=y

CONFIG_GPIO=y

# Make sure printk is printing to the UART console
CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=y

CONFIG_HEAP_MEM_POOL_SIZE=16384

CONFIG_BT=y
CONFIG_BT_PERIPHERAL=y
CONFIG_BT_DEVICE_NAME="Nordic_UART_Service"
CONFIG_BT_DEVICE_APPEARANCE=833
CONFIG_BT_DEVICE_NAME_DYNAMIC=y
CONFIG_BT_MAX_CONN=1
CONFIG_BT_MAX_PAIRED=1

CONFIG_BT_NUS_UART_BUFFER_SIZE=240
CONFIG_UART_0_NRF_TX_BUFFER_SIZE=244
CONFIG_BT_USER_PHY_UPDATE=y
CONFIG_BT_USER_DATA_LEN_UPDATE=y
CONFIG_BT_GAP_AUTO_UPDATE_CONN_PARAMS=n
#CONFIG_SDC_MAX_CONN_EVENT_LEN_DEFAULT=50000

CONFIG_BT_GATT_CLIENT=y
CONFIG_BT_ATT_PREPARE_COUNT=2
CONFIG_BT_CONN_TX_MAX=10
CONFIG_BT_L2CAP_TX_BUF_COUNT=10
CONFIG_BT_L2CAP_DYNAMIC_CHANNEL=y
CONFIG_BT_CTLR_PHY_2M=y
CONFIG_BT_CTLR_RX_BUFFERS=2
CONFIG_BT_BUF_ACL_TX_COUNT=10

CONFIG_BT_BUF_ACL_TX_SIZE=251
CONFIG_BT_CTLR_DATA_LENGTH_MAX=251
CONFIG_BT_BUF_ACL_RX_SIZE=251

# Set output power to +14 dBm (-8 + 22 = +14), SKY66112 PA
CONFIG_BT_CTLR_TX_PWR_MINUS_8=y

# NFC
CONFIG_NFCT_PINS_AS_GPIOS=y

# Enable the NUS service
CONFIG_BT_NUS=y
CONFIG_BT_NUS_UART_ASYNC_ADAPTER=n

# Enable bonding
CONFIG_BT_SETTINGS=y
CONFIG_FLASH=y
CONFIG_FLASH_PAGE_LAYOUT=y
CONFIG_FLASH_MAP=y
CONFIG_NVS=y
CONFIG_SETTINGS=y

# Enable DK LED and Buttons library
CONFIG_DK_LIBRARY=y

# This example requires more workqueue stack
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048

# Config logger
CONFIG_LOG=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_LOG_BACKEND_RTT=n
CONFIG_LOG_BACKEND_UART=y

CONFIG_ASSERT=y

### FEM configration
CONFIG_MPSL=y
CONFIG_MPSL_FEM=y
CONFIG_MPSL_FEM_SIMPLE_GPIO=y

[Kenneth]

Hi,

You can find the maximum mtu size by calling bt_gatt_get_mtu() while in a connection, note that the effective size is ATT_MTU-3 when sending notifications.

If the MTU size is updated during the connection, then you can get information about the new MTU size by something like:

void mtu_updated(struct bt_conn *conn, uint16_t tx, uint16_t rx)
{
    printk("Updated MTU: TX: %d RX: %d bytes\n", tx, rx);
}

static struct bt_gatt_cb gatt_callbacks = {
    .att_mtu_updated = mtu_updated
};

Best regards,
Kenneth

[BradEA]

Thanks, that helped a lot.

Is there a way to be notified if the MTU is changed while on a connection?

[Kenneth]

I would think mtu_updated() callback would be executed on every MTU change?

Kenneth