# Kconfig - kernel configuration options # # Copyright (c) 2014-2015 Wind River Systems, Inc. # # SPDX-License-Identifier: Apache-2.0 # menu "General Kernel Options" config HAS_DTS bool "Uses Device Tree" help This option specifies that the target platform supports device tree configuration. config MULTITHREADING bool prompt "Multi-threading" default y help If disabled, only the main thread is available, so a main() function must be provided. Interrupts are available. Kernel objects will most probably not behave as expected, especially with regards to pending, since the main thread cannot pend, it being the only thread in the system. Many drivers and subsystems will not work with this option; use only when you REALLY know what you are doing. config NUM_COOP_PRIORITIES int prompt "Number of coop priorities" if MULTITHREADING default 16 default 1 if !MULTITHREADING range 0 128 help Number of cooperative priorities configured in the system. Gives access to priorities: K_PRIO_COOP(0) to K_PRIO_COOP(CONFIG_NUM_COOP_PRIORITIES - 1) or seen another way, priorities: -CONFIG_NUM_COOP_PRIORITIES to -1 This can be set to zero to disable cooperative scheduling. Cooperative threads always preempt preemptible threads. Each priority requires an extra 8 bytes of RAM. Each set of 32 extra total priorities require an extra 4 bytes and add one possible iteration to loops that search for the next thread to run. The total number of priorities is NUM_COOP_PRIORITIES + NUM_PREEMPT_PRIORITIES + 1 The extra one is for the idle thread, which must run at the lowest priority, and be the only thread at that priority. config NUM_PREEMPT_PRIORITIES int prompt "Number of preemptible priorities" if MULTITHREADING default 15 default 0 if !MULTITHREADING range 0 128 help Number of preemptible priorities available in the system. Gives access to priorities 0 to CONFIG_NUM_PREEMPT_PRIORITIES - 1. This can be set to 0 to disable preemptible scheduling. Each priority requires an extra 8 bytes of RAM. Each set of 32 extra total priorities require an extra 4 bytes and add one possible iteration to loops that search for the next thread to run. The total number of priorities is NUM_COOP_PRIORITIES + NUM_PREEMPT_PRIORITIES + 1 The extra one is for the idle thread, which must run at the lowest priority, and be the only thread at that priority. config MAIN_THREAD_PRIORITY int prompt "Priority of initialization/main thread" default 0 default -2 if !PREEMPT_ENABLED help Priority at which the initialization thread runs, including the start of the main() function. main() can then change its priority if desired. config COOP_ENABLED bool default y default n if (NUM_COOP_PRIORITIES = 0) config PREEMPT_ENABLED bool default y default n if (NUM_PREEMPT_PRIORITIES = 0) config PRIORITY_CEILING int prompt "Priority inheritance ceiling" default 0 config MAIN_STACK_SIZE int prompt "Size of stack for initialization and main thread" default 1024 help When the initialization is complete, the thread executing it then executes the main() routine, so as to reuse the stack used by the initialization, which would be wasted RAM otherwise. After initialization is complete, the thread runs main(). config IDLE_STACK_SIZE int prompt "Size of stack for idle thread" default 256 default 320 if ARC || (ARM && CPU_HAS_FPU) default 512 if RISCV32 default 1024 if XTENSA help Depending on the work that the idle task must do, most likely due to power management but possibly to other features like system event logging (e.g. logging when the system goes to sleep), the idle thread may need more stack space than the default value. config ISR_STACK_SIZE int prompt "ISR and initialization stack size (in bytes)" default 2048 help This option specifies the size of the stack used by interrupt service routines (ISRs), and during kernel initialization. config THREAD_STACK_INFO bool prompt "Thread stack info" default n help This option allows each thread to store the thread stack info into the k_thread data structure. config THREAD_CUSTOM_DATA bool prompt "Thread custom data" default n help This option allows each thread to store 32 bits of custom data, which can be accessed using the k_thread_custom_data_xxx() APIs. config ERRNO bool prompt "Enable errno support" default y help Enable per-thread errno in the kernel. Application and library code must include errno.h provided by the C library (libc) to use the errno symbol. The C library must access the per-thread errno via the _get_errno() symbol. menu "Kernel Debugging and Metrics" config KERNEL_DEBUG bool prompt "Kernel debugging" default n select INIT_STACKS help Enable kernel debugging. Note that debugging the kernel internals can be very verbose. config BOOT_BANNER bool prompt "Boot banner" default n depends on CONSOLE_HAS_DRIVER select PRINTK select EARLY_CONSOLE help This option outputs a banner to the console device during boot up. It also embeds a date & time stamp in the kernel and in each USAP image. config BUILD_TIMESTAMP bool prompt "Build Timestamp" help Build timestamp and add it to the boot banner. config INT_LATENCY_BENCHMARK bool prompt "Interrupt latency metrics [EXPERIMENTAL]" default n depends on ARCH="x86" help This option enables the tracking of interrupt latency metrics; the exact set of metrics being tracked is board-dependent. Tracking begins when int_latency_init() is invoked by an application. The metrics are displayed (and a new sampling interval is started) each time int_latency_show() is called thereafter. config EXECUTION_BENCHMARKING bool prompt "Timing metrics " default n help This option enables the tracking of various times inside the kernel the exact set of metrics being tracked is board-dependent. All timing measurements are enabled for X86 and ARM based architectures. In other architectures only a subset are enabled. config THREAD_MONITOR bool prompt "Thread monitoring [EXPERIMENTAL]" default n help This option instructs the kernel to maintain a list of all threads (excluding those that have not yet started or have already terminated). endmenu menu "Work Queue Options" config SYSTEM_WORKQUEUE_STACK_SIZE int "System workqueue stack size" default 1024 config SYSTEM_WORKQUEUE_PRIORITY int "System workqueue priority" default -1 default 0 if !COOP_ENABLED default -2 if COOP_ENABLED && !PREEMPT_ENABLED config OFFLOAD_WORKQUEUE_STACK_SIZE int "Workqueue stack size for thread offload requests" default 1024 config OFFLOAD_WORKQUEUE_PRIORITY int "Offload requests workqueue priority" default -1 endmenu menu "Atomic Operations" config ATOMIC_OPERATIONS_BUILTIN bool help Use the compiler builtin functions for atomic operations. This is the preferred method. However, support for all arches in GCC is incomplete. config ATOMIC_OPERATIONS_CUSTOM bool help Use when there isn't support for compiler built-ins, but you have written optimized assembly code under arch/ which implements these. config ATOMIC_OPERATIONS_C bool help Use atomic operations routines that are implemented entirely in C by locking interrupts. Selected by architectures which either do not have support for atomic operations in their instruction set, or haven't been implemented yet during bring-up, and also the compiler does not have support for the atomic __sync_* builtins. endmenu menu "Timer API Options" config TIMESLICING bool "Thread time slicing" default y depends on SYS_CLOCK_EXISTS && (NUM_PREEMPT_PRIORITIES != 0) help This option enables time slicing between preemptible threads of equal priority. config TIMESLICE_SIZE int "Time slice size (in ms)" default 0 range 0 2147483647 depends on TIMESLICING help This option specifies the maximum amount of time a thread can execute before other threads of equal priority are given an opportunity to run. A time slice size of zero means "no limit" (i.e. an infinitely large time slice). config TIMESLICE_PRIORITY int "Time slicing thread priority ceiling" default 0 range 0 NUM_PREEMPT_PRIORITIES depends on TIMESLICING help This option specifies the thread priority level at which time slicing takes effect; threads having a higher priority than this ceiling are not subject to time slicing. config POLL bool prompt "async I/O framework" default n help Asynchronous notification framework. Enable the k_poll() and k_poll_signal() APIs. The former can wait on multiple events concurrently, which can be either directly triggered or triggered by the availability of some kernel objects (semaphores and fifos). endmenu menu "Other Kernel Object Options" config NUM_MBOX_ASYNC_MSGS int "Maximum number of in-flight asynchronous mailbox messages" default 10 help This option specifies the total number of asynchronous mailbox messages that can exist simultaneously, across all mailboxes in the system. Setting this option to 0 disables support for asynchronous mailbox messages. config NUM_PIPE_ASYNC_MSGS int "Maximum number of in-flight asynchronous pipe messages" default 10 help This option specifies the total number of asynchronous pipe messages that can exist simultaneously, across all pipes in the system. Setting this option to 0 disables support for asynchronous pipe messages. endmenu menu "Memory Pool Options" choice prompt "Memory pool block allocation policy" default MEM_POOL_SPLIT_BEFORE_DEFRAG help This option specifies how a memory pool reacts if an unused memory block of the required size is not available. config MEM_POOL_SPLIT_BEFORE_DEFRAG bool "Split a larger block before merging smaller blocks" help This option instructs a memory pool to try splitting a larger unused block if an unused block of the required size is not available; only if no such blocks exist will the memory pool try merging smaller unused blocks. This policy attempts to limit the cost of performing automatic partial defragmentation of the memory pool, at the cost of fragmenting the memory pool's larger blocks. config MEM_POOL_DEFRAG_BEFORE_SPLIT bool "Merge smaller blocks before splitting a larger block" help This option instructs a memory pool to try merging smaller unused blocks if an unused block of the required size is not available; only if this does not generate a sufficiently large block will the memory pool try splitting a larger unused block. This policy attempts to preserve the memory pool's larger blocks, at the cost of performing automatic partial defragmentations more frequently. config MEM_POOL_SPLIT_ONLY bool "Split a larger block, but never merge smaller blocks" help This option instructs a memory pool to try splitting a larger unused block if an unused block of the required size is not available; if no such blocks exist the block allocation operation fails. This policy attempts to limit the cost of defragmenting the memory pool by avoiding automatic partial defragmentation, at the cost of requiring the application to explicitly request a full defragmentation of the memory pool when an allocation fails. Depending on how a memory pool is used, it may be more efficient for a memory pool to perform an occasional full defragmentation than to perform frequent partial defragmentations. endchoice config HEAP_MEM_POOL_SIZE int prompt "Heap memory pool size (in bytes)" default 0 help This option specifies the size of the heap memory pool used when dynamically allocating memory using k_malloc(). Supported values are: 256, 1024, 4096, and 16384. A size of zero means that no heap memory pool is defined. endmenu config ARCH_HAS_CUSTOM_SWAP_TO_MAIN bool # hidden default n help It's possible that an architecture port cannot use _Swap() to swap to the _main() thread, but instead must do something custom. It must enable this option in that case. config SYS_CLOCK_TICKS_PER_SEC int prompt "System tick frequency (in ticks/second)" default 100 help This option specifies the frequency of the system clock in Hz. Depending on the choice made, an amount of possibly expensive math must occur when converting ticks to milliseconds and vice-versa. Some values are optimized, and yield significantly less math. The optimal values from a computational point-of-view are 1000, 500, 250 and 125, since in these cases there is either no computation required, or it is all done via bit-shifting. These also give a granularity from 1ms to 8ms. Other good values are 100, 50, 25, 20 and 10. In this case, some math is required but is minimized. These are also values that necessitate a reduced number of clock interrupts per second, at the cost of granularity (10ms to 100ms). All other values require some extensive 64-bit math, and in some configurations even require calls to compiler built-in functions, and can require a non-trivial extra amount of stack space (e.g. around 80 bytes on x86). config SYS_CLOCK_HW_CYCLES_PER_SEC int "System clock's h/w timer frequency" help This option specifies the frequency of the hardware timer used for the system clock (in Hz). This option is set by the board's Kconfig file and the user should generally avoid modifying it via the menu configuration. config SYS_CLOCK_EXISTS bool # omit prompt to signify a "hidden" option default y default n if (SYS_CLOCK_TICKS_PER_SEC = 0) help This option specifies that the kernel lacks timer support. config INIT_STACKS bool prompt "Initialize stack areas" default n help This option instructs the kernel to initialize stack areas with a known value (0xaa) before they are first used, so that the high water mark can be easily determined. This applies to the stack areas for threads. config XIP bool prompt "Execute in place" help This option allows the kernel to operate with its text and read-only sections residing in ROM (or similar read-only memory). Not all boards support this option so it must be used with care; you must also supply a linker command file when building your image. Enabling this option increases both the code and data footprint of the image. config RING_BUFFER bool prompt "Enable ring buffers" default n help Enable usage of ring buffers. This is similar to kernel FIFOs but ring buffers manage their own buffer memory and can store arbitrary data. For optimal performance, use buffer sizes that are a power of 2. menu "Initialization Priorities" config KERNEL_INIT_PRIORITY_OBJECTS int prompt "Kernel objects initialization priority" default 30 help Kernel objects use this priority for initialization. This priority needs to be higher than minimal default initialization priority. config KERNEL_INIT_PRIORITY_DEFAULT int prompt "Default init priority" default 40 help Default minimal init priority for each init level. config KERNEL_INIT_PRIORITY_DEVICE int prompt "Default init priority for device drivers" default 50 help Device driver, that depends on common components, such as interrupt controller, but does not depend on other devices, uses this init priority. config APPLICATION_INIT_PRIORITY int prompt "Default init priority for application level drivers" default 90 help This priority level is for end-user drivers such as sensors and display which have no inward dependencies. endmenu menu "Security Options" config STACK_CANARIES bool prompt "Compiler stack canaries" default n help This option enables compiler stack canaries support kernel functions. If stack canaries are supported by the compiler, it will emit extra code that inserts a canary value into the stack frame when a function is entered and validates this value upon exit. Stack corruption (such as that caused by buffer overflow) results in a fatal error condition for the running entity. Enabling this option can result in a significant increase in footprint and an associated decrease in performance. If stack canaries are not supported by the compiler, enabling this option has no effect. endmenu source "kernel/Kconfig.event_logger" source "kernel/Kconfig.power_mgmt" endmenu