SMP server FOTA speed

[Alexandre Desgagne]

Hi,

I'm trying to create an application based on the SMP Server app (NCS v1.7.0). I'm able to perform a FOTA using nRF Connect for Mobile and the app._update.bin without any issue but I would like to know if there's a way to increase the speed of the firmware update? The update speed is about 1.6 kB/s or less. Is it a normal behavior?

I tried to update those parameters :

CONFIG_BT_BUF_ACL_RX_SIZE=1024

CONFIG_BT_L2CAP_TX_MTU=1024

The speed increased to 3.0 kB/s but I'm getting this exception in the nRF Connect for Mobile application console.

[McuMgr] "io.runtime.mcumgr.exception.McuMgrErrorException: Mcu Mgr Error: IN_VALUE(3)" received

Here is my prj.conf

# Debug

CONFIG_DEBUG_OPTIMIZATIONS=y

CONFIG_DEBUG_THREAD_INFO=y

# RTT Viewer

CONFIG_USE_SEGGER_RTT=y

CONFIG_RTT_CONSOLE=y

CONFIG_UART_CONSOLE=n

CONFIG_CBPRINTF_FP_SUPPORT=y

# BLE

CONFIG_BT=y

CONFIG_BT_SMP=y

CONFIG_BT_NUS=y

CONFIG_BT_PERIPHERAL=y

# See www.bluetooth.com/.../ for more information about the appearance.

# Generic Sensor

CONFIG_BT_DEVICE_APPEARANCE=1344

CONFIG_BT_DEVICE_NAME="Valve Monitor"

CONFIG_BT_MAX_CONN=2

CONFIG_BT_MAX_PAIRED=2

CONFIG_BT_L2CAP_TX_MTU=252

CONFIG_BT_BUF_ACL_RX_SIZE=256

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2304

# FOTA MCUMGR

CONFIG_MCUMGR=y

CONFIG_MCUMGR_CMD_OS_MGMT=y

CONFIG_MCUMGR_CMD_IMG_MGMT=y

CONFIG_MCUMGR_SMP_BT=y

CONFIG_MCUMGR_SMP_BT_AUTHEN=n

# MCUBoot

CONFIG_BOOTLOADER_MCUBOOT=y

# SAADC

CONFIG_ADC=y

CONFIG_ADC_ASYNC=y

# GPIO

CONFIG_GPIO=y

# WDT

CONFIG_WATCHDOG=y

# Task watchdog

CONFIG_TASK_WDT=y

CONFIG_TASK_WDT_CHANNELS=3

Thanks!

[Amanda Hsieh]

Hi, 

According to the BLE Spec 5.2, vol. 3, Part F, section 3.2.9, it is not possible to have attributes larger than 512 bytes:

"3.2.9 Long attribute values
The longest attribute that can be sent in a single packet is (ATT_MTU-1) octets
in size. At a minimum, the Attribute Opcode is included in an Attribute PDU.
An attribute value may be defined to be larger than (ATT_MTU-1) octets in
size. These attributes are called long attributes.
To read the entire value of an attributes larger than (ATT_MTU-1) octets, the
ATT_READ_BLOB_REQ PDU is used. It is possible to read the first
(ATT_MTU-1) octets of a long attribute value using the ATT_READ_REQ PDU.
To write the entire value of an attribute larger than (ATT_MTU-3) octets, the
ATT_PREPARE_WRITE_REQ and ATT_EXECUTE_WRITE_REQ PDUs are
used. It is possible to write the first (ATT_MTU-3) octets of a long attribute
value using the ATT_WRITE_CMD PDU.
It is not possible to determine if an attribute value is longer than (ATT_MTU-3)
octets using this protocol. A higher layer specification will state that a given
attribute can have a maximum length larger than (ATT_MTU-3) octets.
The maximum length of an attribute value shall be 512 octets.
Note: The protection of an attribute value changing when reading the value
using multiple Attribute protocol PDUs is the responsibility of the higher layer."

You also could take look at this post for setting MTU to 512 bytes. 

Regards,
Amanda