建议客户开启Microlib。
MicroLib is designed for deeply embedded applications.
MicroLib is optimized to use less code and data memory than using the ARM standard library.
MicroLib has been designed to work without an operating system, however this does not prevent it being used together with any OS or RTOS such as Keil RTX.
MicroLib contains no file I/O or wide character support.
As MicroLib has been optimized to minimize code size, some functions will execute more slowly than the standard C library routines available in the ARM compilation tools.
https://www.keil.com/arm/microlib.asp