Example code to set registers in the TMC2208 stepper driver

I am not able to figure out how to set registers over UART in one of these boards, is anyone able to help at all?
There is supposedly a driver library, but I can't make heads or tails of it.

Driver library: TMCStepper - Arduino Reference

I want to enable spreadcycle and try to get he stepper to run at a constant velocity without at pulsing frequency at the driver's input. The datasheet says it is possible but doesn't help beyond that.

Try this.
https://learn.watterott.com/silentstepstick/configurator/

thanks, that may be useful yet. It doesn't help me actually write a program for arduino, but may help answer the question of how noisy the stepper is even when the right options are used. If it's noisy anyway, no point continuing. I don't have an ftdi usb to serial converter though, I may buy one for the occasion. I tried using the arduino mega2650 as the usb to serial device by putting the reset line of the board to ground, causing the mcu to become inert, and then using the right pins on the board to tap into the serial port after the usb to serial converter, but it didin't work for some reason.

part of the problem is that these boards are all slightly different, and there is no documentation. It says there is a jumper that needs to be closed, for instance. On my board there is no jumper. There are also separate pins for the PDN and UART. Not a single pin for them both. It's not clear what I should do with the PDN pin.

The combination and possibilities of things that could be going wrong quickly escalate at each stage where more uncertainty is added, and the whole situation quickly becomes intractable.