# General architecture configuration options # Copyright (c) 2014-2015 Wind River Systems, Inc. # Copyright (c) 2015 Intel Corporation # Copyright (c) 2016 Cadence Design Systems, Inc. # SPDX-License-Identifier: Apache-2.0 # Include these first so that any properties (e.g. defaults) below can be # overridden (by defining symbols in multiple locations) # Note: $ARCH might be a glob pattern source "$(ARCH_DIR)/$(ARCH)/Kconfig" # Architecture symbols # # Should be 'select'ed by low-level symbols like SOC_SERIES_* or, lacking that, # by SOC_*. config ARC bool select ARCH_IS_SET select HAS_DTS imply XIP select ARCH_HAS_THREAD_LOCAL_STORAGE help ARC architecture config ARM bool select ARCH_IS_SET select ARCH_SUPPORTS_COREDUMP if CPU_CORTEX_M select HAS_DTS # FIXME: current state of the code for all ARM requires this, but # is really only necessary for Cortex-M with ARM MPU! select GEN_PRIV_STACKS select ARCH_HAS_THREAD_LOCAL_STORAGE if CPU_CORTEX_R || CPU_CORTEX_M help ARM architecture config ARM64 bool select ARCH_IS_SET select 64BIT select HAS_DTS select HAS_ARM_SMCCC select ARCH_HAS_THREAD_LOCAL_STORAGE select USE_SWITCH select USE_SWITCH_SUPPORTED help ARM64 (AArch64) architecture config SPARC bool select ARCH_IS_SET select HAS_DTS select USE_SWITCH select USE_SWITCH_SUPPORTED select BIG_ENDIAN select ATOMIC_OPERATIONS_BUILTIN if SPARC_CASA select ATOMIC_OPERATIONS_C if !SPARC_CASA select ARCH_HAS_THREAD_LOCAL_STORAGE select ARCH_HAS_EXTRA_EXCEPTION_INFO help SPARC architecture config X86 bool select ARCH_IS_SET select ATOMIC_OPERATIONS_BUILTIN select HAS_DTS select ARCH_SUPPORTS_COREDUMP select CPU_HAS_MMU select ARCH_MEM_DOMAIN_DATA if USERSPACE && !X86_COMMON_PAGE_TABLE select ARCH_MEM_DOMAIN_SYNCHRONOUS_API if USERSPACE select ARCH_HAS_GDBSTUB if !X86_64 select ARCH_HAS_TIMING_FUNCTIONS select ARCH_HAS_THREAD_LOCAL_STORAGE select ARCH_HAS_DEMAND_PAGING select NEED_LIBC_MEM_PARTITION if USERSPACE && TIMING_FUNCTIONS \ && !BOARD_HAS_TIMING_FUNCTIONS \ && !SOC_HAS_TIMING_FUNCTIONS help x86 architecture config NIOS2 bool select ARCH_IS_SET select ATOMIC_OPERATIONS_C select HAS_DTS imply XIP select ARCH_HAS_TIMING_FUNCTIONS help Nios II Gen 2 architecture config RISCV bool select ARCH_IS_SET select HAS_DTS select ARCH_HAS_THREAD_LOCAL_STORAGE imply XIP help RISCV architecture config XTENSA bool select ARCH_IS_SET select HAS_DTS select USE_SWITCH select USE_SWITCH_SUPPORTED imply ATOMIC_OPERATIONS_ARCH help Xtensa architecture config ARCH_POSIX bool select ARCH_IS_SET select HAS_DTS select ATOMIC_OPERATIONS_BUILTIN select ARCH_HAS_CUSTOM_SWAP_TO_MAIN select ARCH_HAS_CUSTOM_BUSY_WAIT select ARCH_HAS_THREAD_ABORT select NATIVE_APPLICATION select HAS_COVERAGE_SUPPORT help POSIX (native) architecture config ARCH_IS_SET bool help Helper symbol to detect SoCs forgetting to select one of the arch symbols above. See the top-level CMakeLists.txt. menu "General Architecture Options" module = ARCH module-str = arch source "subsys/logging/Kconfig.template.log_config" module = MPU module-str = mpu source "subsys/logging/Kconfig.template.log_config" config BIG_ENDIAN bool help This option tells the build system that the target system is big-endian. Little-endian architecture is the default and should leave this option unselected. This option is selected by arch/$ARCH/Kconfig, soc/**/Kconfig, or boards/**/Kconfig and the user should generally avoid modifying it. The option is used to select linker script OUTPUT_FORMAT and command line option for gen_isr_tables.py. config 64BIT bool help This option tells the build system that the target system is using a 64-bit address space, meaning that pointer and long types are 64 bits wide. This option is selected by arch/$ARCH/Kconfig, soc/**/Kconfig, or boards/**/Kconfig and the user should generally avoid modifying it. # Workaround for not being able to have commas in macro arguments DT_CHOSEN_Z_SRAM := zephyr,sram config SRAM_SIZE int "SRAM Size in kB" default $(dt_chosen_reg_size_int,$(DT_CHOSEN_Z_SRAM),0,K) help The SRAM size in kB. The default value comes from /chosen/zephyr,sram in devicetree. The user should generally avoid changing it via menuconfig or in configuration files. config SRAM_BASE_ADDRESS hex "SRAM Base Address" default $(dt_chosen_reg_addr_hex,$(DT_CHOSEN_Z_SRAM)) help The SRAM base address. The default value comes from from /chosen/zephyr,sram in devicetree. The user should generally avoid changing it via menuconfig or in configuration files. if ARC || ARM || ARM64 || NIOS2 || X86 # Workaround for not being able to have commas in macro arguments DT_CHOSEN_Z_FLASH := zephyr,flash config FLASH_SIZE int "Flash Size in kB" default $(dt_chosen_reg_size_int,$(DT_CHOSEN_Z_FLASH),0,K) if (XIP && (ARM ||ARM64)) || !ARM help This option specifies the size of the flash in kB. It is normally set by the board's defconfig file and the user should generally avoid modifying it via the menu configuration. config FLASH_BASE_ADDRESS hex "Flash Base Address" default $(dt_chosen_reg_addr_hex,$(DT_CHOSEN_Z_FLASH)) if (XIP && (ARM || ARM64)) || !ARM help This option specifies the base address of the flash on the board. It is normally set by the board's defconfig file and the user should generally avoid modifying it via the menu configuration. endif # ARM || ARM64 || ARC || NIOS2 || X86 if ARCH_HAS_TRUSTED_EXECUTION config TRUSTED_EXECUTION_SECURE bool "Trusted Execution: Secure firmware image" help Select this option to enable building a Secure firmware image for a platform that supports Trusted Execution. A Secure firmware image will execute in Secure state. It may allow the CPU to execute in Non-Secure (Normal) state. Therefore, a Secure firmware image shall be able to configure security attributions of CPU resources (memory areas, peripherals, interrupts, etc.) as well as to handle faults, related to security violations. It may optionally allow certain functions to be called from the Non-Secure (Normal) domain. config TRUSTED_EXECUTION_NONSECURE depends on !TRUSTED_EXECUTION_SECURE bool "Trusted Execution: Non-Secure firmware image" help Select this option to enable building a Non-Secure firmware image for a platform that supports Trusted Execution. A Non-Secure firmware image will execute in Non-Secure (Normal) state. Therefore, it shall not access CPU resources (memory areas, peripherals, interrupts etc.) belonging to the Secure domain. endif # ARCH_HAS_TRUSTED_EXECUTION config HW_STACK_PROTECTION bool "Hardware Stack Protection" depends on ARCH_HAS_STACK_PROTECTION help Select this option to enable hardware-based platform features to catch stack overflows when the system is running in privileged mode. If CONFIG_USERSPACE is not enabled, the system is always running in privileged mode. Note that this does not necessarily prevent corruption and assertions about the overall system state when a fault is triggered cannot be made. config USERSPACE bool "User mode threads" depends on ARCH_HAS_USERSPACE depends on RUNTIME_ERROR_CHECKS depends on SRAM_REGION_PERMISSIONS select THREAD_STACK_INFO help When enabled, threads may be created or dropped down to user mode, which has significantly restricted permissions and must interact with the kernel via system calls. See Zephyr documentation for more details about this feature. If a user thread overflows its stack, this will be caught and the kernel itself will be shielded from harm. Enabling this option may or may not catch stack overflows when the system is in privileged mode or handling a system call; to ensure these are always caught, enable CONFIG_HW_STACK_PROTECTION. config PRIVILEGED_STACK_SIZE int "Size of privileged stack" default 1024 depends on ARCH_HAS_USERSPACE help This option sets the privileged stack region size that will be used in addition to the user mode thread stack. During normal execution, this region will be inaccessible from user mode. During system calls, this region will be utilized by the system call. This value must be a multiple of the minimum stack alignment. config KOBJECT_TEXT_AREA int "Size of kobject text area" default 512 if COVERAGE_GCOV default 512 if NO_OPTIMIZATIONS default 512 if STACK_CANARIES && RISCV default 256 depends on ARCH_HAS_USERSPACE help Size of kernel object text area. Used in linker script. config KOBJECT_DATA_AREA_RESERVE_EXTRA_PERCENT int "Reserve extra kobject data area (in percentage)" default 100 depends on ARCH_HAS_USERSPACE help Multiplication factor used to calculate the size of placeholder to reserve space for kobject metadata hash table. The hash table is generated via gperf is highly dependent on the absolute addresses of kobjects which might change between prebuilts. To reserve enough space for the hash table during final linking passes to keep kobjects in same place, the size of reserved space is calculated from the first prebuilt plus additional space calculated with this percentage (of the kobject data area in first prebuilt). config KOBJECT_RODATA_AREA_EXTRA_BYTES int "Reserve extra bytes for kobject rodata area" default 16 depends on ARCH_HAS_USERSPACE help Reserve a few more bytes for the RODATA region for kobject metadata. This is to account for the uncertainty of tables generated by gperf. config GEN_PRIV_STACKS bool help Selected if the architecture requires that privilege elevation stacks be allocated in a separate memory area. This is typical of arches whose MPUs require regions to be power-of-two aligned/sized. FIXME: This should be removed and replaced with checks against CONFIG_MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT, but both ARM and ARC changes will be necessary for this. config STACK_GROWS_UP bool "Stack grows towards higher memory addresses" help Select this option if the architecture has upward growing thread stacks. This is not common. config NO_UNUSED_STACK_INSPECTION bool help Selected if the architecture will generate a fault if unused stack memory is examined, which is the region between the current stack pointer and the deepest available address in the current stack region. config MAX_THREAD_BYTES int "Bytes to use when tracking object thread permissions" default 2 depends on USERSPACE help Every kernel object will have an associated bitfield to store thread permissions for that object. This controls the size of the bitfield (in bytes) and imposes a limit on how many threads can be created in the system. config DYNAMIC_OBJECTS bool "Allow kernel objects to be allocated at runtime" depends on USERSPACE help Enabling this option allows for kernel objects to be requested from the calling thread's resource pool, at a slight cost in performance due to the supplemental run-time tables required to validate such objects. Objects allocated in this way can be freed with a supervisor-only API call, or when the number of references to that object drops to zero. config NOCACHE_MEMORY bool "Support for uncached memory" depends on ARCH_HAS_NOCACHE_MEMORY_SUPPORT help Add a "nocache" read-write memory section that is configured to not be cached. This memory section can be used to perform DMA transfers when cache coherence issues are not optimal or can not be solved using cache maintenance operations. menu "Interrupt Configuration" config DYNAMIC_INTERRUPTS bool "Enable installation of IRQs at runtime" help Enable installation of interrupts at runtime, which will move some interrupt-related data structures to RAM instead of ROM, and on some architectures increase code size. config GEN_ISR_TABLES bool "Use generated IRQ tables" help This option controls whether a platform uses the gen_isr_tables script to generate its interrupt tables. This mechanism will create an appropriate hardware vector table and/or software IRQ table. config GEN_IRQ_VECTOR_TABLE bool "Generate an interrupt vector table" default y depends on GEN_ISR_TABLES help This option controls whether a platform using gen_isr_tables needs an interrupt vector table created. Only disable this if the platform does not use a vector table at all, or requires the vector table to be in a format that is not an array of function pointers indexed by IRQ line. In the latter case, the vector table must be supplied by the application or architecture code. config GEN_SW_ISR_TABLE bool "Generate a software ISR table" default y depends on GEN_ISR_TABLES help This option controls whether a platform using gen_isr_tables needs a software ISR table table created. This is an array of struct _isr_table_entry containing the interrupt service routine and supplied parameter. config ARCH_SW_ISR_TABLE_ALIGN int "Alignment size of a software ISR table" default 0 depends on GEN_SW_ISR_TABLE help This option controls alignment size of generated _sw_isr_table. Some architecture needs a software ISR table to be aligned to architecture specific size. The default size is 0 for no alignment. config GEN_IRQ_START_VECTOR int default 0 depends on GEN_ISR_TABLES help On some architectures, part of the vector table may be reserved for system exceptions and is declared separately from the tables created by gen_isr_tables.py. When creating these tables, this value will be subtracted from CONFIG_NUM_IRQS to properly size them. This is a hidden option which needs to be set per architecture and left alone. config IRQ_OFFLOAD bool "Enable IRQ offload" depends on TEST help Enable irq_offload() API which allows functions to be synchronously run in interrupt context. Only useful for test cases that need to validate the correctness of kernel objects in IRQ context. config EXTRA_EXCEPTION_INFO bool "Collect extra exception info" depends on ARCH_HAS_EXTRA_EXCEPTION_INFO help This option enables the collection of extra information, such as register state, when a fault occurs. This information can be useful to collect for post-mortem analysis and debug of issues. endmenu # Interrupt configuration config INIT_ARCH_HW_AT_BOOT bool "Initialize internal architecture state at boot" depends on ARCH_SUPPORTS_ARCH_HW_INIT help This option instructs Zephyr to force the initialization of the internal architectural state (for example ARCH-level HW registers and system control blocks) during boot to the reset values as specified by the corresponding architecture manual. The option is useful when the Zephyr firmware image is chain-loaded, for example, by a debugger or a bootloader, and we need to guarantee that the internal states of the architecture core blocks are restored to the reset values (as specified by the architecture). Note: the functionality is architecture-specific. For the implementation details refer to each architecture where this feature is supported. endmenu # # Architecture Capabilities # config ARCH_HAS_SINGLE_THREAD_SUPPORT bool config ARCH_HAS_TIMING_FUNCTIONS bool config ARCH_HAS_TRUSTED_EXECUTION bool config ARCH_HAS_STACK_PROTECTION bool config ARCH_HAS_USERSPACE bool config ARCH_HAS_EXECUTABLE_PAGE_BIT bool config ARCH_HAS_NOCACHE_MEMORY_SUPPORT bool config ARCH_HAS_RAMFUNC_SUPPORT bool config ARCH_HAS_NESTED_EXCEPTION_DETECTION bool config ARCH_SUPPORTS_COREDUMP bool config ARCH_SUPPORTS_ARCH_HW_INIT bool config ARCH_HAS_EXTRA_EXCEPTION_INFO bool config ARCH_HAS_GDBSTUB bool config ARCH_HAS_COHERENCE bool help When selected, the architecture supports the arch_mem_coherent() API and can link into incoherent/cached memory using the ".cached" linker section. config ARCH_HAS_THREAD_LOCAL_STORAGE bool # # Other architecture related options # config ARCH_HAS_THREAD_ABORT bool # # Hidden CPU family configs # config CPU_HAS_TEE bool help This option is enabled when the CPU has support for Trusted Execution Environment (e.g. when it has a security attribution unit). config CPU_HAS_DCLS bool help This option is enabled when the processor hardware is configured in Dual-redundant Core Lock-step (DCLS) topology. config CPU_HAS_FPU bool help This option is enabled when the CPU has hardware floating point unit. config CPU_HAS_FPU_DOUBLE_PRECISION bool select CPU_HAS_FPU help When enabled, this indicates that the CPU has a double floating point precision unit. config CPU_HAS_MPU bool help This option is enabled when the CPU has a Memory Protection Unit (MPU). config CPU_HAS_MMU bool help This hidden option is selected when the CPU has a Memory Management Unit (MMU). config ARCH_HAS_DEMAND_PAGING bool help This hidden configuration should be selected by the architecture if demand paging is supported. config ARCH_HAS_RESERVED_PAGE_FRAMES bool help This hidden configuration should be selected by the architecture if certain RAM page frames need to be marked as reserved and never used for memory mappings. The architecture will need to implement arch_reserved_pages_update(). config ARCH_MAPS_ALL_RAM bool help This hidden option is selected by the architecture to inform the kernel that all RAM is mapped at boot, and not just the bounds of the Zephyr image. If RAM starts at 0x0, the first page must remain un-mapped to catch NULL pointer dereferences. With this enabled, the kernel will not assume that virtual memory addresses past the kernel image are available for mappings, but instead takes into account an entire RAM mapping instead. This is typically set by architectures which need direct access to all memory. It is the architecture's responsibility to mark reserved memory regions as such in arch_reserved_pages_update(). Although the kernel will not disturb this RAM mapping by re-mapping the associated virtual addresses elsewhere, this is limited to only management of the virtual address space. The kernel's page frame ontology will not consider this mapping at all; non-kernel pages will be considered free (unless marked as reserved) and Z_PAGE_FRAME_MAPPED will not be set. menuconfig MMU bool "Enable MMU features" depends on CPU_HAS_MMU help This option is enabled when the CPU's memory management unit is active and the arch_mem_map() API is available. if MMU config MMU_PAGE_SIZE hex "Size of smallest granularity MMU page" default 0x1000 help Size of memory pages. Varies per MMU but 4K is common. For MMUs that support multiple page sizes, put the smallest one here. config KERNEL_VM_BASE hex "Virtual address space base address" default $(dt_chosen_reg_addr_hex,$(DT_CHOSEN_Z_SRAM)) help Define the base of the kernel's address space. By default, this is the same as the DT_CHOSEN_Z_SRAM physical base SRAM address from DTS, in which case RAM will be identity-mapped. Some architectures may require RAM to be mapped in this way; they may have just one RAM region and doing this makes linking much simpler, as at least when the kernel boots all virtual RAM addresses are the same as their physical address (demand paging at runtime may later modify this for non-pinned page frames). Otherwise, if RAM isn't identity-mapped: 1. It is the architecture's responsibility to transition the instruction pointer to virtual addresses at early boot before entering the kernel at z_cstart(). 2. The underlying architecture may impose constraints on the bounds of the kernel's address space, such as not overlapping physical RAM regions if RAM is not identity-mapped, or the virtual and physical base addresses being aligned to some common value (which allows double-linking of paging structures to make the instruction pointer transition simpler). Zephyr does not implement a split address space and if multiple page tables are in use, they all have the same virtual-to-physical mappings (with potentially different permissions). config KERNEL_VM_OFFSET hex "Kernel offset within address space" default 0 help Offset that the kernel image begins within its address space, if this is not the same offset from the beginning of RAM. Some care may need to be taken in selecting this value. In certain build-time cases, or when a physical address cannot be looked up in page tables, the equation: virt = phys + ((KERNEL_VM_BASE + KERNEL_VM_OFFSET) - (SRAM_BASE_ADDRESS + SRAM_OFFSET)) Will be used to convert between physical and virtual addresses for memory that is mapped at boot. This uncommon and is only necessary if the beginning of VM and physical memory have dissimilar alignment. config KERNEL_VM_SIZE hex "Size of kernel address space in bytes" default 0x800000 help Size of the kernel's address space. Constraining this helps control how much total memory can be used for page tables. The difference between KERNEL_VM_BASE and KERNEL_VM_SIZE indicates the size of the virtual region for runtime memory mappings. This is needed for mapping driver MMIO regions, as well as special RAM mapping use-cases such as VSDO pages, memory mapped thread stacks, and anonymous memory mappings. The kernel itself will be mapped in here as well at boot. Systems with very large amounts of memory (such as 512M or more) will want to use a 64-bit build of Zephyr, there are no plans to implement a notion of "high" memory in Zephyr to work around physical RAM size larger than the defined bounds of the virtual address space. menuconfig DEMAND_PAGING bool "Enable demand paging [EXPERIMENTAL]" depends on ARCH_HAS_DEMAND_PAGING help Enable demand paging. Requires architecture support in how the kernel is linked and the implementation of an eviction algorithm and a backing store for evicted pages. if DEMAND_PAGING config DEMAND_PAGING_ALLOW_IRQ bool "Allow interrupts during page-ins/outs" help Allow interrupts to be serviced while pages are being evicted or retrieved from the backing store. This is much better for system latency, but any code running in interrupt context that page faults will cause a kernel panic. Such code must work with exclusively pinned code and data pages. The scheduler is still disabled during this operation. If this option is disabled, the page fault servicing logic runs with interrupts disabled for the entire operation. However, ISRs may also page fault. config DEMAND_PAGING_PAGE_FRAMES_RESERVE int "Number of page frames reserved for paging" default 32 if !LINKER_GENERIC_SECTIONS_PRESENT_AT_BOOT default 0 help This sets the number of page frames that will be reserved for paging that do not count towards free memory. This is to ensure that there are some page frames available for paging code and data. Otherwise, it would be possible to exhaust all page frames via anonymous memory mappings. config DEMAND_PAGING_STATS bool "Gather Demand Paging Statistics" help This enables gathering various statistics related to demand paging, e.g. number of pagefaults. This is useful for tuning eviction algorithms and optimizing backing store. Should say N in production system as this is not without cost. config DEMAND_PAGING_STATS_USING_TIMING_FUNCTIONS bool "Use Timing Functions to Gather Demand Paging Statistics" select TIMING_FUNCTIONS_NEED_AT_BOOT help Use timing functions to gather various demand paging statistics. config DEMAND_PAGING_THREAD_STATS bool "Gather per Thread Demand Paging Statistics" depends on DEMAND_PAGING_STATS help This enables gathering per thread statistics related to demand paging. Should say N in production system as this is not without cost. config DEMAND_PAGING_TIMING_HISTOGRAM bool "Gather Demand Paging Execution Timing Histogram" depends on DEMAND_PAGING_STATS help This gathers the histogram of execution time on page eviction selection, and backing store page in and page out. Should say N in production system as this is not without cost. config DEMAND_PAGING_TIMING_HISTOGRAM_NUM_BINS int "Number of bins (buckets) in Demand Paging Timing Histogrm" depends on DEMAND_PAGING_TIMING_HISTOGRAM default 10 help Defines the number of bins (buckets) in the histogram used for gathering execution timing information for demand paging. This requires k_mem_paging_eviction_histogram_bounds[] and k_mem_paging_backing_store_histogram_bounds[] to define the upper bounds for each bin. See kernel/statistics.c for information. endif # DEMAND_PAGING endif # MMU menuconfig MPU bool "Enable MPU features" depends on CPU_HAS_MPU help This option, when enabled, indicates to the core kernel that an MPU is enabled. if MPU config MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT bool help This option is enabled when the MPU requires a power of two alignment and size for MPU regions. config MPU_REQUIRES_NON_OVERLAPPING_REGIONS bool help This option is enabled when the MPU requires the active (i.e. enabled) MPU regions to be non-overlapping with each other. config MPU_GAP_FILLING bool "Force MPU to be filling in background memory regions" depends on MPU_REQUIRES_NON_OVERLAPPING_REGIONS default y if !USERSPACE help This Kconfig option instructs the MPU driver to enforce a full kernel SRAM partitioning, when it programs the dynamic MPU regions (user thread stack, PRIV stack guard and application memory domains) during context-switch. We allow this to be a configurable option, in order to be able to switch the option off and have an increased number of MPU regions available for application memory domain programming. Notes: An increased number of MPU regions should only be required, when building with USERSPACE support. As a result, when we build without USERSPACE support, gap filling should always be required. When the option is switched off, access to memory areas not covered by explicit MPU regions is restricted to privileged code on an ARCH-specific basis. Refer to ARCH-specific documentation for more information on how this option is used. endif # MPU config SRAM_REGION_PERMISSIONS bool "Assign appropriate permissions to kernel areas in SRAM" depends on MMU || MPU default y help This option indicates that memory protection hardware is present, enabled, and regions have been configured at boot for memory ranges within the kernel image. If this option is turned on, certain areas of the kernel image will have the following access policies applied for all threads, including supervisor threads: 1) All program text will be have read-only, execute memory permission 2) All read-only data will have read-only permission, and execution disabled if the hardware supports it. 3) All other RAM addresses will have read-write permission, and execution disabled if the hardware supports it. Options such as USERSPACE or HW_STACK_PROTECTION may additionally impose additional policies on the memory map, which may be global or local to the current running thread. This option may consume additional memory to satisfy memory protection hardware alignment constraints. If this option is disabled, the entire kernel will have default memory access permissions set, typically read/write/execute. It may be desirable to turn this off on MMU systems which are using the MMU for demand paging, do not need memory protection, and would rather not use up RAM for the alignment between regions. menu "Floating Point Options" config FPU bool "Enable floating point unit (FPU)" depends on CPU_HAS_FPU help This option enables the hardware Floating Point Unit (FPU), in order to support using the floating point registers and instructions. When this option is enabled, by default, threads may use the floating point registers only in an exclusive manner, and this usually means that only one thread may perform floating point operations. If it is necessary for multiple threads to perform concurrent floating point operations, the "FPU register sharing" option must be enabled to preserve the floating point registers across context switches. Note that this option cannot be selected for the platforms that do not include a hardware floating point unit; the floating point support for those platforms is dependent on the availability of the toolchain- provided software floating point library. config FPU_SHARING bool "FPU register sharing" depends on FPU && MULTITHREADING help This option enables preservation of the hardware floating point registers across context switches to allow multiple threads to perform concurrent floating point operations. Note that some compiler configurations may activate a floating point context by generating FP instructions for any thread, and that context must be preserved when switching such threads in and out. The developers can still disable the FP sharing mode in their application projects, and switch to Unshared FP registers mode, if it is guaranteed that the image code does not generate FP instructions outside the single thread context that is allowed to do so. endmenu menu "Cache Options" config CACHE_MANAGEMENT bool "Enable cache management features" help This links in the cache management functions (for d-cache and i-cache where possible). config DCACHE_LINE_SIZE_DETECT bool "Detect d-cache line size at runtime" depends on CACHE_MANAGEMENT help This option enables querying some architecture-specific hardware for finding the d-cache line size at the expense of taking more memory and code and a slightly increased boot time. If the CPU's d-cache line size is known in advance, disable this option and manually enter the value for DCACHE_LINE_SIZE or set it in the DT using the 'd-cache-line-size' property. config DCACHE_LINE_SIZE int "d-cache line size" if !DCACHE_LINE_SIZE_DETECT depends on CACHE_MANAGEMENT default 0 help Size in bytes of a CPU d-cache line. If this is set to 0 the value is obtained from the 'd-cache-line-size' DT property instead if present. Detect automatically at runtime by selecting DCACHE_LINE_SIZE_DETECT. config ICACHE_LINE_SIZE_DETECT bool "Detect i-cache line size at runtime" depends on CACHE_MANAGEMENT help This option enables querying some architecture-specific hardware for finding the i-cache line size at the expense of taking more memory and code and a slightly increased boot time. If the CPU's i-cache line size is known in advance, disable this option and manually enter the value for ICACHE_LINE_SIZE or set it in the DT using the 'i-cache-line-size' property. config ICACHE_LINE_SIZE int "i-cache line size" if !ICACHE_LINE_SIZE_DETECT depends on CACHE_MANAGEMENT default 0 help Size in bytes of a CPU i-cache line. If this is set to 0 the value is obtained from the 'i-cache-line-size' DT property instead if present. Detect automatically at runtime by selecting ICACHE_LINE_SIZE_DETECT. choice CACHE_TYPE prompt "Cache type" depends on CACHE_MANAGEMENT default HAS_ARCH_CACHE config HAS_ARCH_CACHE bool "Integrated cache controller" help "Integrade on-core cache controller" config HAS_EXTERNAL_CACHE bool "External cache controller" help "External cache controller or cache management system" endchoice endmenu config ARCH string help System architecture string. config SOC string help SoC name which can be found under soc//. This option holds the directory name used by the build system to locate the correct linker and header files for the SoC. config SOC_SERIES string help SoC series name which can be found under soc///. This option holds the directory name used by the build system to locate the correct linker and header files. config SOC_FAMILY string help SoC family name which can be found under soc//. This option holds the directory name used by the build system to locate the correct linker and header files. config BOARD string help This option holds the name of the board and is used to locate the files related to the board in the source tree (under boards/). The Board is the first location where we search for a linker.ld file, if not found we look for the linker file in soc/// config TOOLCHAIN_HAS_BUILTIN_FFS bool default y if !(64BIT && RISCV) help Hidden option to signal that toolchain has __builtin_ffs*().