shorten packet to fit into BLE large packets

[pelikhan]

Use BLE large packets and use 242bytes or something.

[jamesadevine]

What do you mean? Isn't the MTU of BLE really small? https://stackoverflow.com/questions/38913743/maximum-packet-length-for-bluetooth-le

[jamesadevine]

Do all devices support the ATT packet extension?

[pelikhan]

James to look at this.

[jamesadevine]

@pelikhan @mmoskal

I've spoke to Martin Woolley at the Bluetooth SIG and he says that not every device will have the same MTU. This means that packet chunking will be required for some devices anyway.

As a result, I think we should account for packet chunking in the design of the BLE physical layer. This means we can keep the current packet size and layout of JACDAC frames.

Thoughts?

[jamesadevine]

(this is a similar approach to what we already do with say USB + HF2)

[mmoskal]

isn't there a common size? we don't really care about all devices, I think we care about nrf52 and maybe esp32; I assume all laptops/phones would support the max size?

[jamesadevine]

@mmoskal It depends which version of BLE we are talking about. BLE 5.2 (Vol 3 Part F) supports an ATT value of up to 512 bytes.

For version 4.2, the LE data extension has variable support. From reading around, iPhones support an LE extension of around 185 bytes. I believe this is fixed and cannot be modified by applications.

We could design only for BLE 5.2 if we think that's the way to go...

[mmoskal]

OK, let's go with fragmentation then

[jamesadevine]

I think either way, the current packet and frame layout does not need to be modified to account for BLE specifically. Agree?

[mmoskal]

Correct.