DFU - Device Manager Question - Payload(250 bytes) too long for MTU: 249

[PingISTL]

Dear support

Try to perform DFU OTA on my final target board and have an error state says - "payload(250 bytes) too long for MTU: 249 "during uploading stage, could anyone let me know what is happening please? 

I have done quite a few times on a Fanstel board and had not have any problem.

Urgent help is needed please!

Ping

[tonkarhu]

I had the same problem today while testing my app. My solution was to downgrade "no.nordicsemi.android:mcumgr-ble:1.5.0" to "no.nordicsemi.android:mcumgr-ble:1.4.1". The problem is related to this change: https://github.com/NordicSemiconductor/Android-nRF-Connect-Device-Manager/pull/84#issue-1467771449 .

I added new issue: https://github.com/NordicSemiconductor/Android-BLE-Library/issues/447#issue-1477071185

[AHaug]

PingISTL can you verify if this also fixes your issue?

If not, you could try to increase the MTU size. You can refer to the prj.conf of Bluetooth: Throughput to add the following config settings:

CONFIG_BT_BUF_ACL_RX_SIZE=251
CONFIG_BT_BUF_ACL_TX_SIZE=251
CONFIG_BT_L2CAP_TX_MTU=247
CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

This should increase both the max. MTU size and maximum radio packet length, so it may be sufficient to only increase the MTU size

Kind regards,
Andreas

[PingISTL]

Here is current setting of my prj.conf:

# Allow for large Bluetooth data packets.

CONFIG_BT_L2CAP_TX_MTU=252

CONFIG_BT_BUF_ACL_RX_SIZE=256

Looks bigger than your recommendation, will try others, but not sure which one is critical?

Thank you for your reply!

Ping

[PingISTL]

Tried to change the setting as above, still not working unfortunately - state message changes to "Payload (246 bytes) too long for MTU: 244"

I think you are right , it is a bug on new version.

Ping

[AHaug]

Yes, the two settings you mention are larger than what I suggested, so I don't think the issue is due to the MTU size since you get the same error. You could try to increase it to 512 and see if that makes any difference. 

I believe it is a max length mtu -1  issue as Tonkarthu suggests. I've reached out to the mobile team and asked about how to proceed. I'll get back to you when I know more. In the meanwhile you might try to downgrade the Device Manager App to see if that fixes the issue.

Kind regards,
Andreas

[PingISTL]

Thank you for reply, tried to downgrade and it works now.

It is a bug for me in new version

Ping