Tweaks on receiver side to receive more messages

[riceman0]

Hello, we are using SDK 5.2.0, SoftDevice 6.2.1 S110 on the peripheral side and S130 on the central side.

We have implemented a serial data link between the two, the central sends ASCII queries to the peripheral along the lines of "[Q5]" and the peripheral replies with [Q5=723]".  The peripheral will internally queue up the message characters, and when the message is complete ']' or if the attribute is full (17 chars) it will send the data via the softdevice using 

sd_ble_gatts_hvx(p_sys->conn_handle, &params)

then the central receives an event BLE_GATTC_EVT_HVX from the softdevice, and it extracts the data and processes it.  This all works great.

On a recent build this queuing system may have been broken, and it is sending a message via sd_ble_gatts_hvx on every character.  So on the receiver side we get one character per BLE_GATTC_EVT_HVX.  This would work fine except we are losing some of the characters; in other words we are receiving events for the '[', 'Q', '5', '=', '7', and the rest are apparently lost.

It is very desirable for us to fix this issue on the receiver/central side rather than the sender/peripheral side.  Obviously we should fix the queuing system on the sender, but in the meantime is there anything we can tweak on the receiver end to allow us to receive more events??  Any buffer sizes or timing parameters that would increase our chances of handling ten quick events in succession (I understand the lost characters may not actually be transmitted, but they might also be lost after receipt, it's unclear at this point)

Any levers we can pull on the receiver side to allow complete messages?  Thanks very much for any help!

[run_ar]

I am sorry, I do not think there are anything you can do on the receiver to fix this. If the rx buffers are full the central will simply stop sending packets, or nack packets. Even when sending notifications the LL is safe in the sense that you will not lose packets here. So you need to check the returned error code when calling sd_ble_gatts_hvx on the peripheral and make sure you try to retransmit in case the TX buffers are occupied.

[riceman0]

Thank you very much.  So there is no way to change the size of the RX buffers?  Is that definite or is there a chance of an obscure setting?

[run_ar]

On the s130 you can change the bandwidth when calling sd_ble_enable by configuring the ble_conn_bw_counts_t setting. Check the S110 api for a similar setting.