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

The radio surely wouldn't work, since the carrier frequency would be far too high, and the flash memory would not be able to keep up at the higher speeds. Most likely the chip would crash completely because of some internal timing violations.
Usually devices like these are designed to tolerate a certain amount of drift (up to 10% for instance), but once you go beyond that various things on the device are bound to fail. Since we don't test the chip under these conditions we can only guess what would happen.

Try overclocking your desktop CPU to double the frequency, and I am sure you will see similar issues ;)

I don't know if we have tested with WiFi disabled in the settings, but I am pretty sure the ~670kbps limit is enforced by the phone regardless.
I would be happy to be proven wrong in this case :)

Best regards