How many BLE packets can the SoftDevice queue internally with multi-link connections? (Multiple connections)

[droberson]

Hardware:

nRF52840 (Central)

nRF52840 (Peripheral)

nrf52840 (Peripheral)

Software:

SoftDevice S140 6.1.0

SDK 15.2.0_9412b96

Hello,

I was unable to find the answer to this question on the DevZone or Google. As the subject states, how many BLE packets can the SoftDevice queue internally with multi-link connections? Normally this is maxed at 6 for single connections. What is this number when NRF_SDH_BLE_CENTRAL_LINK_COUNT is changed from 1 to 2? Does it become 6 per connection, or 6 for all connections?

For context, my goal is to transmit as many packets in a single connection interval as possible from a central to multiple peripheral devices . On past single-connection based projects I have worked on, I do this by calling sd_ble_gattc_write() until NRF_ERROR_RESOURCES is received, at which I then wait for BLE_GATTC_EVT_WRITE_CMD_TX_COMPLETE before sending more data. My fear is that using the same approach for a single connection in a multi-link configuration will starve the other connections if indeed the SoftDevice internal packet queue is limited to 6 packets for all connections.

Thanks!

Derek

[Kenneth]

Hi,

Normally this is maxed at 6 for single connections. What is this number when NRF_SDH_BLE_CENTRAL_LINK_COUNT is changed from 1 to 2? Does it become 6 per connection, or 6 for all connections?

The simple answer is yes. I recommend to check out nrf_sdh_ble_default_cfg_set() to find that there are many configurations possible, you might also want to increase NRF_SDH_BLE_GATT_MAX_MTU_SIZE to allow larger packets to be sent.

Kenneth

[droberson]

Hey Kenneth,

Yes to which? 6 packets per connection or 6 for all connections?

Thanks,

Derek

[Kenneth]

Sorry, I meant "6 packets per connection".

[droberson]

That was what I needed to know, thanks!