NRF52/BLE4.2 data data throughout

[simon]

Hi,

When i used nrf51822, i remember the s110 define max transmit buffer as 23 Bytes, but now, i am using nrf52832, the max transimit buffer is defined as 158 bytes. Does this is the general standard define in offical BLE 4.2? if so, is it means if i use 20ms for an interval, then, with nrf51822, the data throughout is about 23/20=1kbyte/s . and, with nrf52832, the data throughtout rate can achieve about 158/20=8kbyte/s. Am i right on this?

any one can help on this, it would be very grateful, thanks.

Regards Simon

[endnode]

Not really, BT SIG leaves "default" ATT_MTU size unchanged on 23 bytes. Devices can exchange maximum MTU size capabilities once during the link and since then maximum size implicitly moves the the lower of two max values exchanged. This is managed by S132/140 Soft Devices on nRF52 chip where larger ATT_MTU sizes are supported (it seems never coming to nRF51 with Nordic Soft Devices due to RAM constrains).

Throughput is directly influenced by ATT_MTU size (if you run on top of (G)ATT layer of course;), you can see some example computation in the respective section of Nordic BT 4.2/5.0 throughput blog post. As you can see resulting throughput is also influenced by LL packet size aka PDU because higher-layer ATT_MTU must be split among several packets (and maximum sizes influence how much overhead you need to have).