BLUENRG-MS characteristic update truncated at 20 bytes

[Asela Leelaratne]

Posted on February 12, 2018 at 06:04

Hi,

I'm using BLUENRG-MS (SPBTLE-RF) module for a low power BLE application. I'm having issues with pushing updates from the module to a mobile device.

Issue:

The BLE H/W is acting as a peripheral device and a mobile is acting as a central device.

Characteristic size is 93 bytes.

When a read is triggered from the mobile device, full 93 bytes is received.

If I subscribe for change notifications from the mobile device, and update the characteristic data on the peripheral, only the first 20 bytes are received at the mobile device.

Why is the update limited to 20 bytes ?

Is there a way to increase the update buffer size ?

I've been searching the internet and looking at STM documentation but couldn't find a reasonable explanation for this. Not even for the 20 byte limit.

Can you point me towards the correct documentation.

Test H/W:  X-NUCLEO-IDB05A1 on a NUCLEO-L496ZG-P

IDB05A1 F/W: 7.2.c (0x723)

BLE Stack:  BLUENRG V3.0.0 running on L496

Thanks,

Asela.

#x-nucleo-idb05a1 #ble #bluenrg-ms #idb05a1 #mtu

[Andrea Palmieri · Accepted solution]

Posted on February 12, 2018 at 11:47

Hi Asela,

as reported in an other

https://community.st.com/0D50X00009XkXaRSAV

, BlueNRG-MS does not support an ATT_MTU greater than 20 bytes. The Characteristic can be read (not notified) in chunks, thus the mobile device is able to receive the full length when a read is triggered.

Kind regards

Andrea

[Asela Leelaratne]

Posted on February 12, 2018 at 13:09

Hi Andrea,

Thanks for the quick response.

This definitely sheds light towards solving my problem.

I did see that thread and asked for some information there as well.

As mentioned in that thread is this a product specific limitation?

Is this information documented somewhere in the product documentation? If so, can you point me to it.

The intention of these questions is to present this as evidence to my team/client and continue ahead with a workaround.

Thanks in advance.

Best Regards,

Asela.

[Andrea Palmieri]

Posted on February 12, 2018 at 15:44

Hi Asela,

you can refer to the

https://launchstudio.bluetooth.com/ListingDetails/8875

 on the Bluetooth SIG website. Among other product characteristics, you can find (in Table LL 9/6) that 'LE Data Packet Length Extension = FALSE'. Hope that can provide the evidence you need.

Kind regards

Andrea 

[Asela Leelaratne]

Posted on February 13, 2018 at 00:33

Hi Andrea,

Thanks for your help.

I'll follow up on the documentation.

Best Regards,

Asela.