Which USB class should I use for maximum data rates on nrf52840? And what is the maximum size of transfer if I use CDC_ACM?

[Akshay]

I want to transfer sensor data to a raspberry pi using the in-built USB on nrf52840. The example codes have the following classes: CDC_ACM, Audio, HID and Mass storage. I want to transfer data around 200 KB/s. Which class would be sufficient for the data rates? Also for the host side, will using USB serial port (ttyACM0) be fast enough for CDC_ACM or should I use libusb?

[Radoslaw Koppel]

According to our tests Windows CDC driver limits throughput to something around 2 Mbps. So it might be just fine for you. The fastest one seems to be MSC, but it would require quite a lot of tricks to use it to download logs. If CDC would not be fast enough I would go with libusb and accessing endpoints directly - it seems to be much easier than using MSC.

[Akshay]

Thank you, I'll see if I can get the required data rates using CDC. Is there an example code for NRF52840 if I use libusb to access endpoints directly?

[bjorn-spockeli]

I think you should be able to use the USBD example in examples\peripheral\usbd\pca10056 as a template, which uses the USB Device raw IP driver, see this Infocenter page for the documentation.

[Akshay]

Thank you Bjorn Spockeli. Got the USBD template code working for my application with libusb

[alexlöddeköpinge]

Hi, maybe this answer is too old but I try. What do you mean when you say "go with libusb and accessing endpoint directly"?

[bjorn-spockeli]

Libusb is a cross-platform user library to access USB devices on windows, linux mac etc. By accessing the endpoint directly we simply mean fetching the data received over USB directly from the receive buffer instead of letting the windows driver fetch it for you as this may lead to limited throughput in some scenarios.