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]

You seems to be missing how BLE stack works: it needs to have all the packets prepared before connection interval starts. If you have 50ms interval then at the start SD will try to send as many packets as possible (meaning they must be already in the queue, SD must have certain bandwidth configured for the link and also the peer on the other side must be able to proceed with multiple PDUs) but then whatever you will try to push through TX buffers won't get transmitted before next connection interval. So I don't get what you fiddle with 10ms and 5ms delays if your interval is 50ms. Moreover the Link Layer inside the stack is more or less asynchronous to what you do in your application on top. The fact that you got callback on TX_COMPLETE even doesn't mean that packet was sent NOW. There are many timing differences which can take long milliseconds, don't try to measure time like this.