Bare machine C with floating-point processing
If you want to use floating-point processing in an application without the C library, there are a number of requirements you must fulfill.
These requirements are:
__rt_raise()if you are using the heap.
- Not define
main(), to avoid linking in the library initialization code.
Write an assembly language veneer that establishes the register state required to run C. This veneer must branch to the entry function in your application. The register state required to run C primarily comprises the stack pointer.
The register state also consists of
sb, the static base register, if Read/Write Position-Independent (RWPI) code applies.
- Provide your own RW/ZI initialization code.
- Ensure that your initialization veneer is executed by, for example, placing it in your reset handler.
- Use the appropriate FPU option when you build your application.
_fp_init()to initialize the floating-point status register before performing any floating-point operations.
Do not build your application with the
-ffp-mode=fast. In such cases, you can also define the function
__rt_fp_status_addr()to return the address of a writable data word to be used instead of the floating-point status register. If you rely on the default library definition of
__rt_fp_status_addr(), this word resides in the program data section, unless you define
__user_perthread_libspace()(or in the case of legacy code that does not yet use