There are a few options.
- Create a new set of files/functions based on the current library.
- Use Silicon Labs EUSART config and autogenerated functions (eg from a Simplicity Studio project).
- Use the “bare metal” UARTDRV library.
- Use the “very bare metal” em_eusart driver.
- Use Simplicity Studio for the project, ie not Arduino.
Personally the 5th option is what I’d choose but that’s because I’m familiar with the development process…
1st option is probably easiest for Arduino. Rest are slightly more difficult.
For 1st option, implement similar functions to those of Serial1.