BLE Object Transfer Service on STM32WB5MMG

[crwper]

AN5669 seems to indicate that the BLE Object Transfer Service is available on STM32WB devices. Are there any technical documents or examples showing how this would be used in an STM32Cube application?

[Remy ISSALYS · Accepted solution]

Hello,

BLE Object Transfer Service example is not delivered in STM32CubeWB package. According to OTS specification, this service provides management and control features supporting bulk data transfers which occur via a separate
L2CAP connection-oriented channel. To implement this service, you can refer to:

• BLE_COC_DataTransfer example available on STM32 Hotspot GitHub which allows to exchange data through L2CAP COC. 
• BLE_Custom example and this wiki page to see how to add the service and characteristic needed using STM32CubeMX tool. 

Best Regards

[crwper]

Thanks, Remy! That's exactly what I needed.

[crwper]

I've just run into an issue implementing OTS using CubeMX. It appears that each service is limited to 5 characteristics, but the OTS requires up to 12 characteristics in total. Is it possible to increase the limit of 5 characteristics in CubeMX?

[Remy ISSALYS]

Hello,

Indeed, for STM32WB series, each service is limited to 5 characteristics, the additional characteristics can't be managed by CubeMX tool and need to be added in user section. This limitation has been moved to 25 services and 25 characteristics for each service for STM32WBA series. 

Best Regards

[crwper]

I'm not quite sure I understand where the limitation is coming from. I have the impression the limitation is in the CubeMX tool only, but when you mention that the limit is different for the STM32WBA processors, I wonder if this is a limitation in the BLE stack itself. What is the maximum number of services/characteristics which can be added for the STM32WB series if I write the code myself rather than going through CubeMX?

Thanks!

[Remy ISSALYS]

Hello,

Indeed, the limitation comes from CubeMX tool only. 

Best Regards

[crwper]

Thanks, Remy!

Can you give me some idea why the limit is different for the two processors, if the limit is only in CubeMX? This is a bit confusing for me.

Is there any limit in the hardware itself--i.e., how many services and characterstics can the STM32WB support if I write the code myself rather than using CubeMX?

[Remy ISSALYS]

Hello,

The limitation comes from CubeMX tool only, the limitation is different between STM32WB and STM32WBA because the management of service and characteristic inside CubeMX tool have been improved for STM32WBA series, inside the tool it's not done by the same way for STM32WB series.

On another hand, you refer to the following wiki pages to see the limitation for the GATT database size which link to the size of SRAM allocated for the GATT database (see part 5). 

Best Regards

[crwper]

Thanks again, Remy!