4.2. Nuclei C Runtime Library for Nuclei Toolchain

4.2.1. Usage

You can use prebuilt libncrt library for both Nuclei GNU and LLVM toolchain to replace libgcc(-lgcc), newlib c(-lc/-lc_nano) and math(-lm) library.

If you want to select a small variant of libncrt library, with basic ‘heapops’ and uart ‘fileops’, you can use it like below:

For Nuclei GNU Toolchain(riscv64-unknown-elf-gcc) case:

riscv64-unknown-elf-gcc --specs=libncrt_small.specs -Wl,--start-group -lheapops_basic -lfileops_uart -Wl,--end-group

For Nuclei LLVM Toolchain(riscv64-unknown-elf-clang) case:

You can’t use –specs=libncrt_small.specs option, since it is not supported, gcc can also use following command just like clang.

riscv64-unknown-elf-clang -nodefaultlibs -isystem=/include/libncrt -Wl,--start-group -lncrt_small -lheapops_basic -lfileops_uart -Wl,--end-group

For details about libncrt, ‘heapops’ and ‘fileops’ variant, please read following documentation.

When using this method, please don’t link with -lm/lc_nano/-lgcc/-lc library to avoid potential linker error and code size increasement.

4.2.2. Varieties

4.2.2.1. Libncrt Library choice

	GCC Specs	Library
Fast	libncrt_fast.specs	libncrt_fast.a
Balanced	libncrt_balanced.specs	libncrt_balanced.a
Small	libncrt_small.specs	libncrt_small.a
Nano	libncrt_nano.specs	libncrt_nano.a
Pico	libncrt_pico.specs	libncrt_pico.a

If you are not using gcc, and want to use libncrt small variant, you can pass -isystem=/include/libncrt during compile phase, and -nodefaultlibs -lncrt_small during link phase.

4.2.2.2. Optimization

	Optimization
Fast	Favor speed at the expense of size
Balanced	Balanced
Small	Favor size at the expense of speed
Nano	Favor size at the expense of speed
Pico	Favor size at the expense of speed

4.2.2.3. Formatted I/O

	int	long	long long	float	double	wide character	input character class	Width and precision specification	stdout formatting buffer (byte)
Fast	yes	yes	yes	yes	yes	yes	yes	yes	64
Balanced	yes	yes	yes	yes	yes	yes	yes	yes	64
Small	yes	yes	yes	yes	yes	yes	yes	yes	64
Nano	yes	yes	yes	no	no	no	no	yes	64
Pico	yes	no	no	no	no	no	no	no	32

4.2.2.4. Algorithm

	Scaled-integer Algorithm
Fast	Algorithms use C-language floating-point arithmetic.
Balanced	Algorithms use C-language floating-point arithmetic.
Small	Algorithms use C-language floating-point arithmetic.
Nano	Algorithms use C-language floating-point arithmetic.
Pico	IEEE single-precision functions use scaled integer arithmetic if there is a scaled-integer implementation of the function.

4.2.2.5. Extra fileops and heapops libraries used together with libncrt

	Library Type	Library description
-lfileops_uart	fileops	Using a UART for I/O, need to implement at least metal_tty_putc and metal_tty_getc
-lfileops_semi	fileops	Using semihosting for I/O
-lfileops_rtt	fileops	Using SEGGER RTT for I/O
-lheapops_basic	heapops	Using a basic heap implementation
-lheapops_realtime	heapops	Using a real-time heap implementation
-lheapops_minimal	heapops	Using a minimal heap implementation