Just like when using GPRs, you must use assembly code to interact with the FPU. We recommend you read through floating-point control instructions (table 3-18) that you can perform on an FPU.
As mentioned before, you will not be working with the individual FPU registers but rather the entire FPU save state as a whole. Therefore, if you find yourself trying to work with each st register individually, take a step back and reread through the aforementioned floating-point control instructions.
When you are writing assembly, you may either do so directly in
.S files or in-line among C code using
asm. Most likely, you will have to do both. We recommend you read through a guide on
asm to familiarize yourself. You may also find it helpful to reference some other parts of the code that use
asm can seem daunting, but keep in mind, at its core, it’s just writing assembly instructions instead of C!