I have three USB dongles that report themselves being CSR8510 A10. The only difference is reported REV number, but I could not find any information about CSR8510 A10 revisions.
Two of them are labeled by the manufacturer as Bluetooth 2.1-only, the third (unbranded cheap from Aliexpress) was labeled as CSR 4.0.
CSR specifications for CSR8510 A10 say that this chip is:
Fully qualified Bluetooth v4.0 system
Dual-mode Bluetooth/Bluetooth low energy operation
I have tested the dongles in operation and indeed BLE utilities report that the 2.1 dongles are not supported while the 4.0 dongle works fine.
How does it come that two of my dongles support only Bluetooth 2.1 although all three of them report being CSR8510 A10?
Full VID&PID reports follow:
-
Unbranded CSR (this one was tested to be indeed 4.0 and working as a BLE device):
USB\VID_0A12&PID_0001&REV_8891, Bus reported device description: CSR8510 A10 -
Esperanza Bluetooth 2.1:
USB\VID_0A12&PID_0001&REV_0134, Bus reported device description: CSR8510 A10 -
KWorld Bluetooth 2.1:
USB\VID_0A12&PID_0001&REV_0134, Bus reported device description: CSR8510 A10
Best Answer
Bluetooth 4 includes features 2.0 and up. It is possible that the 2.1 devices do not support the enhancements from 3.0 and 4.0.
3.0 introduced HS (High Speed) which uses a WiFi-like transport mechanism to achieve speeds above the normal 3Mbps of Bluetooth 2.1. it is entirely possible that this might need an additional amplifier or physical chip to properly enable it.
They could all have the same core chip, but the 2.1 devices are missing a key device to enable high speed or the Bluetooth Low Energy modes that define the 4.0 spec.
See https://en.wikipedia.org/wiki/Bluetooth#Specifications_and_features