Queued Write Service Halts when trying to write to characteristic

[jloliveira]

Good afternoon,

I'm using nRF52840 with SDK15 and Softdevice6.0.0.

I'm using the Queued Write Service Module to make use of a characteristic able to receive up to 510bytes of data.

I tested the queued write service through the ble_app_queued_writes with NRF_BLE_QWRS_MAX_RCV_SIZE = 510 and MEM_BUFF_SIZE = 686 and it works OK when trying to write data through nRFConnect with 21-510bytes size.

When I integrate exactly the same code on my application I had to set NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE to a minimum of 1832 and increase the RAM size respectively to avoid NRF_ERROR_NO_MEM as I have 6 more services with 1-6 characteristics each. Yet, when attempting to write data through the queued write characteristic through nRFConnect the app keeps spinning until it timeouts, no matter the size of the data I to write. Do you have any idea why this is happening and can you please help me solve this issue?

Also, I want to be able to write data <20bytes through the same characteristic. Is there any way to achieve this?

Thank you,

João

[jloliveira]

Good afternoon,

Just discovered I was missing the nrf_ble_qwr_conn_handle_assign(&m_qwr, m_conn_handle); line in the BLE_GAP_EVT_CONNECTED event which was causing the hanging, so now the problem is solved.

Yet, I still need to find a way to write data with <20bytes through the same characteristic. Is there any way to achieve this?

Also, I can only write a maximum of 510bytes of data with the Queued Write Service but I would need 1024bytes. How can I accomplish it?

Thank you,

João

[jloliveira]

Good afternoon,

Could anyone please look into the questions I made above?

Thank you,

João

[bjorn-spockeli]

Hi Joao, 

I sincerley apologize for the very late reply. 

If you want to send more than 20bytes at the time then you need to increase the BLE_QWRS_MAX_CHAR_LEN. 

The maximum size of a fixed length GATT Server Attribute( i.e. the size of a characteristic value) is restricted to BLE_GATTS_FIX_ATTR_LEN_MAX which is 510bytes. Hence this is the largest characteristic size you can set with the S132 v6.0.0 SoftDevice. 

Best regards

Bjørn 

[jloliveira]

Hi Bjørn,

Thank you for your reply.

The question is how to write data with less than 20bytes onto the same queued write characteristic, and if it would be possible to write more than 510bytes.

 

Thank you,

João

[bjorn-spockeli]

Hi João, 

You are right that something is not quite right qhen writing less than 20 bytes, i.e. BLE_QWRS_MAX_CHAR_LEN bytes, to the QWR characteristic. I will need to look into this by doing a sniffer trace and examine the on-air packets. 

As for more thatn 510 bytes, as I stated in my previous reply the maximum size of a fixed length GATT Server Attribute( i.e. the size of a characteristic value) is restricted to BLE_GATTS_FIX_ATTR_LEN_MAX which is 510bytes. Hence this is the largest characteristic size you can set with the S132 v6.0.0 SoftDevice. So you will not be able to write more than 510 bytes to the QWR characteristic as this is the maximum size of a characteristic value.

Bjørn