esp-idf/components/esp_libc/Kconfig

menu "LibC"

    choice LIBC
        prompt "LibC to build application with"
        default LIBC_NEWLIB if IDF_TOOLCHAIN_CLANG
        default LIBC_PICOLIBC

        config LIBC_NEWLIB
            bool "NewLib"
        config LIBC_PICOLIBC
            bool "Picolibc"
            depends on !IDF_TOOLCHAIN_CLANG
    endchoice

    config LIBC_PICOLIBC_NEWLIB_COMPATIBILITY
        bool "Provides limited interoperability with libraries built using Newlib headers"
        default y
        depends on LIBC_PICOLIBC
        help
            This option provides limited compatibility with libraries built using Newlib headers by:

            Enabling hidden system-header inclusions that exist in Newlib.
            Adding tls_stdio, tls_stdout, and tls_stderr variables to Thread Local Storage
            to allow prebuilt libraries to access them via getreent().
            Providing an implementation of getreent() that returns the value of the thread-pointer register.

            Limitations:

            1. If your application or an external prebuilt library accesses Newlib "struct _reent" implicitly,
            this may cause memory corruption on the task stack. You have two options:

            - Use libc API calls instead of directly accessing "struct _reent" fields.
            - Switch ESP-IDF to use the Newlib implementation by setting CONFIG_LIBC_NEWLIB=y in sdkconfig.

            2. If your application uses a prebuilt library built with Newlib headers, you may encounter
            unexpected behavior when overriding stdin, stdout, and stderr. External prebuilt libraries
            can only read these streams, so overriding them will not affect as it was for Newlib.
            You have two options to fix this:

            - Rebuild the library with Picolibc headers that follow POSIX-standardized stdin, stdout,
              and stderr declarations.
            - Switch ESP-IDF to use the Newlib implementation by setting CONFIG_LIBC_NEWLIB=y in sdkconfig.


    config LIBC_MISC_IN_IRAM
        bool "Place misc libc functions (abort/assert/stdatomics) in IRAM" if SPI_FLASH_AUTO_SUSPEND
        default y

    config LIBC_LOCKS_PLACE_IN_IRAM
        bool "Place lock API in IRAM"
        default y
        help
            Enable this option to include be able to call the lock API from
            code that runs while cache is disabled, e.g. IRAM interrupts.

    choice LIBC_STDOUT_LINE_ENDING
        prompt "Line ending for console output"
        default LIBC_STDOUT_LINE_ENDING_CRLF
        depends on VFS_SUPPORT_IO
        help
            This option allows configuring the desired line endings sent to console
            when a newline ('\n', LF) appears on stdout.
            Three options are possible:

            CRLF: whenever LF is encountered, prepend it with CR

            LF: no modification is applied, stdout is sent as is

            CR: each occurrence of LF is replaced with CR

            This option doesn't affect behavior of the UART driver (drivers/uart.h).

        config LIBC_STDOUT_LINE_ENDING_CRLF
            bool "CRLF"
        config LIBC_STDOUT_LINE_ENDING_LF
            bool "LF"
        config LIBC_STDOUT_LINE_ENDING_CR
            bool "CR"
    endchoice

    choice LIBC_STDIN_LINE_ENDING
        prompt "Line ending for console input"
        default LIBC_STDIN_LINE_ENDING_CR
        depends on VFS_SUPPORT_IO
        help
            This option allows configuring which input sequence on console produces
            a newline ('\n', LF) on stdin.
            Three options are possible:

            CRLF: CRLF is converted to LF

            LF: no modification is applied, input is sent to stdin as is

            CR: each occurrence of CR is replaced with LF

            This option doesn't affect behavior of the UART driver (drivers/uart.h).

        config LIBC_STDIN_LINE_ENDING_CRLF
            bool "CRLF"
        config LIBC_STDIN_LINE_ENDING_LF
            bool "LF"
        config LIBC_STDIN_LINE_ENDING_CR
            bool "CR"
    endchoice

    config LIBC_NEWLIB_NANO_FORMAT
        bool "Enable 'nano' formatting options for printf/scanf family"
        default y if IDF_TARGET_ESP32C2
        depends on LIBC_NEWLIB
        help
            In most chips the ROM contains parts of newlib C library, including printf/scanf family
            of functions. These functions have been compiled with so-called "nano"
            formatting option. This option doesn't support 64-bit integer formats and C99
            features, such as positional arguments.

            For more details about "nano" formatting option, please see newlib readme file,
            search for '--enable-newlib-nano-formatted-io':
            https://sourceware.org/git/?p=newlib-cygwin.git;a=blob_plain;f=newlib/README;hb=HEAD

            If this option is enabled and the ROM contains functions from newlib-nano, the build system
            will use functions available in ROM, reducing the application binary size.
            Functions available in ROM run faster than functions which run from flash. Functions available
            in ROM can also run when flash instruction cache is disabled.

            Some chips (e.g. ESP32-C6) has the full formatting versions of printf/scanf in ROM instead of
            the nano versions and in this building with newlib nano might actually increase the size of
            the binary. Which functions are present in ROM can be seen from ROM caps:
            ESP_ROM_HAS_NEWLIB_NANO_FORMAT and ESP_ROM_HAS_NEWLIB_NORMAL_FORMAT.

            If you need 64-bit integer formatting support or C99 features, keep this
            option disabled.

    choice LIBC_TIME_SYSCALL
        prompt "Timers used for gettimeofday function"
        default LIBC_TIME_SYSCALL_USE_RTC_HRT
        help
            This setting defines which hardware timers are used to
            implement 'gettimeofday' and 'time' functions in C library.

            - If both high-resolution (systimer for all targets except ESP32)
                and RTC timers are used, timekeeping will continue in deep sleep.
                Time will be reported at 1 microsecond resolution.
                This is the default, and the recommended option.
            - If only high-resolution timer (systimer) is used, gettimeofday will
                provide time at microsecond resolution.
                Time will not be preserved when going into deep sleep mode.
            - If only RTC timer is used, timekeeping will continue in
                deep sleep, but time will be measured at 6.(6) microsecond
                resolution. Also the gettimeofday function itself may take
                longer to run.
            - If no timers are used, gettimeofday and time functions
                return -1 and set errno to ENOSYS; they are defined as weak,
                so they could be overridden.
                If you want to customize gettimeofday() and other time functions,
                please choose this option and refer to the 'time.c' source file
                for the exact prototypes of these functions.

            - When RTC is used for timekeeping, two RTC_STORE registers are
                used to keep time in deep sleep mode.

        config LIBC_TIME_SYSCALL_USE_RTC_HRT
            bool "RTC and high-resolution timer"
            select ESP_TIME_FUNCS_USE_RTC_TIMER
            select ESP_TIME_FUNCS_USE_ESP_TIMER
        config LIBC_TIME_SYSCALL_USE_RTC
            bool "RTC"
            select ESP_TIME_FUNCS_USE_RTC_TIMER
        config LIBC_TIME_SYSCALL_USE_HRT
            bool "High-resolution timer"
            select ESP_TIME_FUNCS_USE_ESP_TIMER
        config LIBC_TIME_SYSCALL_USE_NONE
            bool "None"
            select ESP_TIME_FUNCS_USE_NONE
    endchoice

    config LIBC_OPTIMIZED_MISALIGNED_ACCESS
        bool "Use performance-optimized memXXX/strXXX functions on misaligned memory access"
        default y
        depends on ESP_ROM_HAS_SUBOPTIMAL_NEWLIB_ON_MISALIGNED_MEMORY
        help
            Enables performance-optimized implementations of memory and string functions
            when handling misaligned memory.

            Require approximately 800–1000 bytes of IRAM.

            Optimized functions include:
                - memcpy
                - memset
                - memmove
                - str[n]cpy
                - str[n]cmp

    config LIBC_ASSERT_BUFFER_SIZE
        int "Assert message buffer size"
        range 100 2048
        default 200
        help
            Size of the buffer used to format assert failure messages.

            When assertions fail, the system formats a message containing the function name,
            file name, line number, and the failed expression. This option controls the
            maximum length of this message.

            If you encounter truncated assert messages (especially with C++ templates or
            long function names), increase this value. The default value of 200 bytes
            should be sufficient for most cases, but complex template expressions may
            require larger buffers.

endmenu # LibC

config STDATOMIC_S32C1I_SPIRAM_WORKAROUND
    bool
    default SPIRAM && (IDF_TARGET_ESP32 || IDF_TARGET_ESP32S3) && !IDF_TOOLCHAIN_CLANG # TODO IDF-9032