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]

Yes, this is the right direction. Note that there is (or used to be) some bandwidth management for each "GAP" link which Soft Device manages so just set this feature according to your needs and then make sure that your GATT API calls are in line with actual ATT_MTU size (e.g. you cannot send longer GATT Notification from Server side then is actual ATT_MTU size - 3B of GATT header). The rest should just work automatically.

[Stayhungry]

I guess you're talking about something like LE Packet Length Extension, and I'll pay close attention to the ATT_MTU message that Exchange MTU PDU brings, lol.

Thank you very much

[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.

[Stayhungry]

Because I'm researching BLE and nordic are not deeper than you, so I can only understand what you mean: Nordic's "GAP" link has a limited bandwidth allocated to each link, but I feel like you are talking about LL layer's state machines. If there are 8 connections at the same time, the bandwidth for each connection will be limited. If this is your concern, my device supports only one connection, so it should not be affected, but thank you for your suggestion.

[endnode]

GAP means BT SIG Generic Access Profile layer, in our case implemented inside Nordic stack. I believe you should read all on-line resources because they answer like 99% of the questions you post here.