maximum baudrate nrf52 slower than BLE 5.0

[thefool]

Hi, we're starting to plan an update to BLE 5.0 (specifically the double bandwidth feature) on a product using the nRF521832 connected to an STM32. We were just testing increasing our internal communication speed, and realised the nRF52 is limiting us to "Up to 1 Mbps baudrate"

That's slower than the net OTA bandwidth of ~1.4Mbps!

Any chance we could double that? My suggestions would be:

1. using 8x oversampling rather than 16x?
2. utilising a faster clock (PCLK32M) when available?

Thanks!

PS: we'll be outputting the nordics clock on a GPIO to drive the clock input on the STM32, so clock drift between the two devices should not be an issue for us ;-)

[ovrebekk]

Hi

I can't think of any easy and reliable way to achieve serial communication higher than 1MBaud if you only have 2 GPIO's available.

With 3 GPIO's you could do uni-directional SPI up to 4MHz at least (bi-directional if you have 4 GPIO's).

Do you really need to transfer data continuously at a rate higher than 1Mbps?
Keep in mind that 1.4Mbps is the absolute maximum bandwidth, and in practical use the actual bandwidth is likely to be lower than this. By optimizing the application for a lower bandwidth you will have some bandwidth left over for retransmission, making the link more reliable and the data rate more consistent.

Best regards
Torbjørn Øvrebekk

[ovrebekk]

Hi

For better or worse we design most of the serial interfaces ourselves, trying to enforce a unified look and feel (including the task/event registers that are used in all Nordic peripherals). This includes the UART, which sets the baudrate exclusively through the BAUDRATE register.

Both the iPhone 8 and X support the high speed mode introduced by Bluetooth 5.
The connection interval when achieving the highest speed is 15ms.
The main limitation in the latest iPhones regarding speed is the event length, which is capped to 50% of the connection interval. This means you are only allowed to send packet for 50% of the available time, even if the connection interval is small. This is probably done to ensure sufficient RF time for other RF protocols (like WiFi or classic Bluetooth), but also means that you will not achieve the highest possible speeds that Bluetooth 5 is capable of.

Best regards