sd_ble_gatts_hvx cache

[Stayhungry]

1、how long will it take for me to cache?

Once I call sd_ble_gatts_hvx, assuming tx_queue is large enough, how long can I cache data to softdeivce?

For example, I called sd_ble_gatts_hvx once, and then called again after 5ms. Can I cache successfully,Or the data has been sent out? Why?

2、Cached data and the size of the actual packet sent

If ATT_MTU is set to 247, LL payload = 251, tx_queue = 2, should I get NO_RESOURCE once if I call sd_ble_gatts_hvx(buffer, buffer len = 100) third times ?

This time actually sent the package which payload len = 200byte?

Thanks

[endnode]

1. How long? Doesn't make sense. Tx queue size is partially configurable in Nordic Soft Device and how much time it takes to flush it over BLE that's impossible to say as it depends on how BLE connection link performs at that moment (what is the interval, what is packet loss etc.) So forget about time, there is no guaranteed time when it comes to radio like BLE.
2. Tx queue size in Nordic Soft Device should have "slots" so on (G)ATT layer it can hold certain number of packets regardless the size. So you can get BLE_ERROR_NO_TX_BUFFERS error code in response if you try to push some more outgoing packets but there is no available Tx slot on (G)ATT layer in the SD. The size doesn't matter.

[endnode]

Not really, PDU extension is something completely different then ATT_MTU size/extension (but both indeed influence throughput). And none of these are actually set in Nordic SD bandwidth per link, that is simply saying how many PDUs will it be able to send within connection interval (max) and all that based on connection interval and number of concurrent links. So while some simplifications might be made to this complex picture you need to understand that on the background there are many combinations.