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]

(3/3)

1. Once data re ready to be sent make GATT packets from them (= you might need to fragment) and push to SD queue through the API until it will say no TX buffers available.
2. Wait for TX complete event and try to push again.
3. Repeat steps 1 and 2 until all packets are left from your APP. Then wait for new data to be sent and go to step 1 again.

So you actually should manage your own queue in APP layer on top of similar queue in Soft Device.