# Heap Memory Allocation

[中文]

## Stack and Heap

ESP-IDF applications use the common computer architecture patterns of stack (dynamic memory allocated by program control flow), heap (dynamic memory allocated by function calls), and static memory (memory allocated at compile time).

Because ESP-IDF is a multi-threaded RTOS environment, each RTOS task has its own stack. By default, each of these stacks is allocated from the heap when the task is created. See `xTaskCreateStatic()` for the alternative where stacks are statically allocated.

Because ESP32-S2 uses multiple types of RAM, it also contains multiple heaps with different capabilities. A capabilities-based memory allocator allows apps to make heap allocations for different purposes.

For most purposes, the C Standard Library's `malloc()` and `free()` functions can be used for heap allocation without any special consideration. However, in order to fully make use of all of the memory types and their characteristics, ESP-IDF also has a capabilities-based heap memory allocator. If you want to have a memory with certain properties (e.g., DMA-Capable Memory or executable-memory), you can create an OR-mask of the required capabilities and pass that to `heap_caps_malloc()`.

## Memory Capabilities

The ESP32-S2 contains multiple types of RAM:

- DRAM (Data RAM) is memory that is connected to CPU's data bus and is used to hold data. This is the most common kind of memory accessed as a heap.

- IRAM (Instruction RAM) is memory that is connected to the CPU's instruction bus and usually holds executable data only (i.e., instructions). If accessed as generic memory, all accesses must be aligned to 32-Bit Accessible Memory.

- D/IRAM is RAM that is connected to CPU's data bus and instruction bus, thus can be used either Instruction or Data RAM.

For more details on these internal memory types, see Memory Types.

It is also possible to connect external SPI RAM to the ESP32-S2. The external RAM is integrated into the ESP32-S2's memory map via the cache, and accessed similarly to DRAM.

All DRAM memory is single-byte accessible, thus all DRAM heaps possess the `MALLOC_CAP_8BIT` capability. Users can call `heap_caps_get_free_size(MALLOC_CAP_8BIT)` to get the free size of all DRAM heaps.

When calling `malloc()`, the ESP-IDF `malloc()` internally calls `heap_caps_malloc_default(size)`. This will allocate memory with the capability `MALLOC_CAP_DEFAULT`, which is byte-addressable.

Because `malloc()` uses the capabilities-based allocation system, memory allocated using `heap_caps_malloc()` can be freed by calling the standard `free()` function.

## Available Heap

### DRAM

At startup, the DRAM heap contains all data memory that is not statically allocated by the app. Reducing statically-allocated buffers increases the amount of available free heap.

To find the amount of statically allocated memory, use the idf.py size command.

Note

At runtime, the available heap DRAM may be less than calculated at compile time, because, at startup, some memory is allocated from the heap before the FreeRTOS scheduler is started (including memory for the stacks of initial FreeRTOS tasks).

### IRAM

At startup, the IRAM heap contains all instruction memory that is not used by the app executable code.

The idf.py size command can be used to find the amount of IRAM used by the app.

### D/IRAM

Some memory in the ESP32-S2 is available as either DRAM or IRAM. If memory is allocated from a D/IRAM region, the free heap size for both types of memory will decrease.

### Heap Sizes

At startup, all ESP-IDF apps log a summary of all heap addresses (and sizes) at level Info:

    I (252) heap_init: Initializing. RAM available for dynamic allocation:
    I (259) heap_init: At 3FFAE6E0 len 00001920 (6 KiB): DRAM
    I (265) heap_init: At 3FFB2EC8 len 0002D138 (180 KiB): DRAM
    I (272) heap_init: At 3FFE0440 len 00003AE0 (14 KiB): D/IRAM
    I (278) heap_init: At 3FFE4350 len 0001BCB0 (111 KiB): D/IRAM
    I (284) heap_init: At 4008944C len 00016BB4 (90 KiB): IRAM

### Finding Available Heap

See Heap Information.

## Special Capabilities

### DMA-Capable Memory

Use the `MALLOC_CAP_DMA` flag to allocate memory which is suitable for use with hardware DMA engines (for example SPI and I2S). This capability flag excludes any external PSRAM.

The EDMA hardware feature allows DMA buffers to be placed in external PSRAM, but there may be additional alignment constraints. Consult the ESP32-S2 Technical Reference Manual for details. To allocate a DMA-capable external memory buffer, use the `MALLOC_CAP_SPIRAM | MALLOC_CAP_DMA` capabilities flags; the heap allocator will take care of alignment requirements imposed by the cache and DMA subsystems. If a peripheral has additional alignment requirements, you can use `heap_caps_aligned_alloc()` with the necessary alignment specified.

### 32-Bit Accessible Memory

If a certain memory structure is only addressed in 32-bit units, for example, an array of ints or pointers, it can be useful to allocate it with the `MALLOC_CAP_32BIT` flag. This also allows the allocator to give out IRAM memory, which is sometimes unavailable for a normal `malloc()` call. This can help to use all the available memory in the ESP32-S2.

Memory allocated with `MALLOC_CAP_32BIT` can only be accessed via 32-bit reads and writes, any other type of access will generate a fatal LoadStoreError exception.

### External SPI Memory

When external RAM is enabled, external SPI RAM can be allocated using standard `malloc` calls, or via `heap_caps_malloc(MALLOC_CAP_SPIRAM)`, depending on the configuration. See Configuring External RAM for more details.

## Thread Safety

Heap functions are thread-safe, meaning they can be called from different tasks simultaneously without any limitations.

It is technically possible to call `malloc`, `free`, and related functions from interrupt handler (ISR) context (see Calling Heap-Related Functions from ISR). However, this is not recommended, as heap function calls may delay other interrupts. It is strongly recommended to refactor applications so that any buffers used by an ISR are pre-allocated outside of the ISR. Support for calling heap functions from ISRs may be removed in a future update.

## Calling Heap-Related Functions from ISR

The following functions from the heap component can be called from the interrupt handler (ISR):

- `heap_caps_malloc()`

- `heap_caps_malloc_default()`

- `heap_caps_realloc_default()`

- `heap_caps_malloc_prefer()`

- `heap_caps_realloc_prefer()`

- `heap_caps_calloc_prefer()`

- `heap_caps_free()`

- `heap_caps_realloc()`

- `heap_caps_calloc()`

- `heap_caps_aligned_alloc()`

- `heap_caps_aligned_free()`

Note

However, this practice is strongly discouraged.

## Heap Tracing & Debugging

The following features are documented on the Heap Memory Debugging page:

- Heap Information (free space, etc.)

- Heap Allocation and Free Function Hooks

- Heap Corruption Detection

- Heap Tracing (memory leak detection, monitoring, etc.)

## Implementation Notes

Knowledge about the regions of memory in the chip comes from the "SoC" component, which contains memory layout information for the chip, and the different capabilities of each region. Each region's capabilities are prioritized, so that (for example) dedicated DRAM and IRAM regions are used for allocations ahead of the more versatile D/IRAM regions.

Each contiguous region of memory contains its own memory heap. The heaps are created using the multi_heap functionality. `multi_heap` allows any contiguous region of memory to be used as a heap.

The heap capabilities allocator uses knowledge of the memory regions to initialize each individual heap. Allocation functions in the heap capabilities API will find the most appropriate heap for the allocation based on desired capabilities, available space, and preferences for each region's use, and then calling `multi_heap_malloc()` for the heap situated in that particular region.

Calling `free()` involves finding the particular heap corresponding to the freed address, and then call `multi_heap_free()` on that particular `multi_heap` instance.

## API Reference - Heap Allocation

### Header File

- components/heap/include/esp_heap_caps.h

- This header file can be included with:

  >     #include "esp_heap_caps.h"

### Functions

esp_err_t heap_caps_register_failed_alloc_callback(esp_alloc_failed_hook_t callback)

  registers a callback function to be invoked if a memory allocation operation fails

  Parameters:

    callback -- caller defined callback to be invoked

  Returns:

    ESP_OK if callback was registered.

void *heap_caps_malloc(size_t size, uint32_t caps)

  Allocate a chunk of memory which has the given capabilities.

  Equivalent semantics to libc malloc(), for capability-aware memory.

  Parameters:

    - size -- Size, in bytes, of the amount of memory to allocate

    - caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory to be returned

  Returns:

    A pointer to the memory allocated on success, NULL on failure

void heap_caps_free(void *ptr)

  Free memory previously allocated via heap_caps_malloc() or heap_caps_realloc().

  Equivalent semantics to libc free(), for capability-aware memory.

  In IDF, `free(p)` is equivalent to `heap_caps_free(p)`.

  Parameters:

    ptr -- Pointer to memory previously returned from heap_caps_malloc() or heap_caps_realloc(). Can be NULL.

void *heap_caps_realloc(void *ptr, size_t size, uint32_t caps)

  Reallocate memory previously allocated via heap_caps_malloc() or heap_caps_realloc().

  Equivalent semantics to libc realloc(), for capability-aware memory.

  In IDF, `realloc(p, s)` is equivalent to `heap_caps_realloc(p, s, MALLOC_CAP_8BIT)`.

  'caps' parameter can be different to the capabilities that any original 'ptr' was allocated with. In this way, realloc can be used to "move" a buffer if necessary to ensure it meets a new set of capabilities.

  Parameters:

    - ptr -- Pointer to previously allocated memory, or NULL for a new allocation.

    - size -- Size of the new buffer requested, or 0 to free the buffer.

    - caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory desired for the new allocation.

  Returns:

    Pointer to a new buffer of size 'size' with capabilities 'caps', or NULL if allocation failed.

void *heap_caps_aligned_alloc(size_t alignment, size_t size, uint32_t caps)

  Allocate an aligned chunk of memory which has the given capabilities.

  Equivalent semantics to libc aligned_alloc(), for capability-aware memory.

  Parameters:

    - alignment -- How the pointer received needs to be aligned must be a power of two

    - size -- Size, in bytes, of the amount of memory to allocate

    - caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory to be returned

  Returns:

    A pointer to the memory allocated on success, NULL on failure

void heap_caps_aligned_free(void *ptr)

  Used to deallocate memory previously allocated with heap_caps_aligned_alloc.

  Note

  This function is deprecated, please consider using heap_caps_free() instead

  Parameters:

    ptr -- Pointer to the memory allocated

void *heap_caps_aligned_calloc(size_t alignment, size_t n, size_t size, uint32_t caps)

  Allocate an aligned chunk of memory which has the given capabilities. The initialized value in the memory is set to zero.

  Parameters:

    - alignment -- How the pointer received needs to be aligned must be a power of two

    - n -- Number of continuing chunks of memory to allocate

    - size -- Size, in bytes, of a chunk of memory to allocate

    - caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory to be returned

  Returns:

    A pointer to the memory allocated on success, NULL on failure

void *heap_caps_calloc(size_t n, size_t size, uint32_t caps)

  Allocate a chunk of memory which has the given capabilities. The initialized value in the memory is set to zero.

  Equivalent semantics to libc calloc(), for capability-aware memory.

  In IDF, `calloc(p)` is equivalent to `heap_caps_calloc(p, MALLOC_CAP_8BIT)`.

  Parameters:

    - n -- Number of continuing chunks of memory to allocate

    - size -- Size, in bytes, of a chunk of memory to allocate

    - caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory to be returned

  Returns:

    A pointer to the memory allocated on success, NULL on failure

size_t heap_caps_get_total_size(uint32_t caps)

  Get the total size of all the regions that have the given capabilities.

  This function takes all regions capable of having the given capabilities allocated in them and adds up the total space they have.

  Parameters:

    caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory

  Returns:

    total size in bytes

size_t heap_caps_get_free_size(uint32_t caps)

  Get the total free size of all the regions that have the given capabilities.

  This function takes all regions capable of having the given capabilities allocated in them and adds up the free space they have.

  Note

  Note that because of heap fragmentation it is probably not possible to allocate a single block of memory of this size. Use heap_caps_get_largest_free_block() for this purpose.

  Parameters:

    caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory

  Returns:

    Amount of free bytes in the regions

size_t heap_caps_get_minimum_free_size(uint32_t caps)

  Get the total minimum free memory of all regions with the given capabilities.

  This adds all the low watermarks of the regions capable of delivering the memory with the given capabilities.

  Note

  Note the result may be less than the global all-time minimum available heap of this kind, as "low watermarks" are tracked per-region. Individual regions' heaps may have reached their "low watermarks" at different points in time. However, this result still gives a "worst case" indication for all-time minimum free heap.

  Parameters:

    caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory

  Returns:

    Amount of free bytes in the regions

size_t heap_caps_get_largest_free_block(uint32_t caps)

  Get the largest free block of memory able to be allocated with the given capabilities.

  Returns the largest value of `s` for which `heap_caps_malloc(s, caps)` will succeed.

  Parameters:

    caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory

  Returns:

    Size of the largest free block in bytes.

esp_err_t heap_caps_monitor_local_minimum_free_size_start(void)

  Start monitoring the value of minimum_free_bytes from the moment this function is called instead of from startup.

  Note

  This allows to detect local lows of the minimum_free_bytes value that wouldn't be detected otherwise.

  Returns:

    esp_err_t ESP_OK if the function executed properly ESP_FAIL if called when monitoring already active

esp_err_t heap_caps_monitor_local_minimum_free_size_stop(void)

  Stop monitoring the value of minimum_free_bytes. After this call the minimum_free_bytes value calculated from startup will be returned in heap_caps_get_info and heap_caps_get_minimum_free_size.

  Returns:

    esp_err_t ESP_OK if the function executed properly ESP_FAIL if called when monitoring not active

void heap_caps_get_info(multi_heap_info_t *info, uint32_t caps)

  Get heap info for all regions with the given capabilities.

  Calls multi_heap_info() on all heaps which share the given capabilities. The information returned is an aggregate across all matching heaps. The meanings of fields are the same as defined for multi_heap_info_t, except that `minimum_free_bytes` has the same caveats described in heap_caps_get_minimum_free_size().

  Parameters:

    - info -- Pointer to a structure which will be filled with relevant heap metadata.

    - caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory

void heap_caps_print_heap_info(uint32_t caps)

  Print a summary of all memory with the given capabilities.

  Calls multi_heap_info on all heaps which share the given capabilities, and prints a two-line summary for each, then a total summary.

  Parameters:

    caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory

bool heap_caps_check_integrity_all(bool print_errors)

  Check integrity of all heap memory in the system.

  Calls multi_heap_check on all heaps. Optionally print errors if heaps are corrupt.

  Calling this function is equivalent to calling heap_caps_check_integrity with the caps argument set to MALLOC_CAP_INVALID.

  Note

  Please increase the value of `CONFIG_ESP_INT_WDT_TIMEOUT_MS` when using this API with PSRAM enabled.

  Parameters:

    print_errors -- Print specific errors if heap corruption is found.

  Returns:

    True if all heaps are valid, False if at least one heap is corrupt.

bool heap_caps_check_integrity(uint32_t caps, bool print_errors)

  Check integrity of all heaps with the given capabilities.

  Calls multi_heap_check on all heaps which share the given capabilities. Optionally print errors if the heaps are corrupt.

  See also heap_caps_check_integrity_all to check all heap memory in the system and heap_caps_check_integrity_addr to check memory around a single address.

  Note

  Please increase the value of `CONFIG_ESP_INT_WDT_TIMEOUT_MS` when using this API with PSRAM capability flag.

  Parameters:

    - caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory

    - print_errors -- Print specific errors if heap corruption is found.

  Returns:

    True if all heaps are valid, False if at least one heap is corrupt.

bool heap_caps_check_integrity_addr(intptr_t addr, bool print_errors)

  Check integrity of heap memory around a given address.

  This function can be used to check the integrity of a single region of heap memory, which contains the given address.

  This can be useful if debugging heap integrity for corruption at a known address, as it has a lower overhead than checking all heap regions. Note that if the corrupt address moves around between runs (due to timing or other factors) then this approach won't work, and you should call heap_caps_check_integrity or heap_caps_check_integrity_all instead.

  Note

  The entire heap region around the address is checked, not only the adjacent heap blocks.

  Parameters:

    - addr -- Address in memory. Check for corruption in region containing this address.

    - print_errors -- Print specific errors if heap corruption is found.

  Returns:

    True if the heap containing the specified address is valid, False if at least one heap is corrupt or the address doesn't belong to a heap region.

void heap_caps_malloc_extmem_enable(size_t limit)

  Enable malloc() in external memory and set limit below which malloc() attempts are placed in internal memory.

  When external memory is in use, the allocation strategy is to initially try to satisfy smaller allocation requests with internal memory and larger requests with external memory. This sets the limit between the two, as well as generally enabling allocation in external memory.

  Parameters:

    limit -- Limit, in bytes.

void *heap_caps_malloc_prefer(size_t size, size_t num, ...)

  Allocate a chunk of memory as preference in decreasing order.

  Attention

    The variable parameters are bitwise OR of MALLOC_CAP_* flags indicating the type of memory. This API prefers to allocate memory with the first parameter. If failed, allocate memory with the next parameter. It will try in this order until allocating a chunk of memory successfully or fail to allocate memories with any of the parameters.

  Parameters:

    - size -- Size, in bytes, of the amount of memory to allocate

    - num -- Number of variable parameters

  Returns:

    A pointer to the memory allocated on success, NULL on failure

void *heap_caps_realloc_prefer(void *ptr, size_t size, size_t num, ...)

  Reallocate a chunk of memory as preference in decreasing order.

  Parameters:

    - ptr -- Pointer to previously allocated memory, or NULL for a new allocation.

    - size -- Size of the new buffer requested, or 0 to free the buffer.

    - num -- Number of variable parameters

  Returns:

    Pointer to a new buffer of size 'size', or NULL if allocation failed.

void *heap_caps_calloc_prefer(size_t n, size_t size, size_t num, ...)

  Allocate a chunk of memory as preference in decreasing order.

  Parameters:

    - n -- Number of continuing chunks of memory to allocate

    - size -- Size, in bytes, of a chunk of memory to allocate

    - num -- Number of variable parameters

  Returns:

    A pointer to the memory allocated on success, NULL on failure

void heap_caps_dump(uint32_t caps)

  Dump the full structure of all heaps with matching capabilities.

  Prints a large amount of output to serial (because of locking limitations, the output bypasses stdout/stderr). For each (variable sized) block in each matching heap, the following output is printed on a single line:

  - Block address (the data buffer returned by malloc is 4 bytes after this if heap debugging is set to Basic, or 8 bytes otherwise).

  - Data size (the data size may be larger than the size requested by malloc, either due to heap fragmentation or because of heap debugging level).

  - Address of next block in the heap.

  - If the block is free, the address of the next free block is also printed.

  Parameters:

    caps -- Bitwise OR of MALLOC_CAP_* flags indicating the type of memory

void heap_caps_dump_all(void)

  Dump the full structure of all heaps.

  Covers all registered heaps. Prints a large amount of output to serial.

  Output is the same as for heap_caps_dump.

size_t heap_caps_get_allocated_size(void *ptr)

  Return the size that a particular pointer was allocated with.

  Note

  The app will crash with an assertion failure if the pointer is not valid.

  Parameters:

    ptr -- Pointer to currently allocated heap memory. Must be a pointer value previously returned by heap_caps_malloc, malloc, calloc, etc. and not yet freed.

  Returns:

    Size of the memory allocated at this block.

void heap_caps_walk(uint32_t caps, heap_caps_walker_cb_t walker_func, void *user_data)

  Function called to walk through the heaps with the given set of capabilities.

  Parameters:

    - caps -- The set of capabilities assigned to the heaps to walk through

    - walker_func -- Callback called for each block of the heaps being traversed

    - user_data -- Opaque pointer to user defined data

void heap_caps_walk_all(heap_caps_walker_cb_t walker_func, void *user_data)

  Function called to walk through all heaps defined by the heap component.

  Parameters:

    - walker_func -- Callback called for each block of the heaps being traversed

    - user_data -- Opaque pointer to user defined data

### Structures

struct walker_heap_info

  Structure used to store heap related data passed to the walker callback function.

  Public Members

  intptr_t start

    Start address of the heap in which the block is located.

  intptr_t end

    End address of the heap in which the block is located.

struct walker_block_info

  Structure used to store block related data passed to the walker callback function.

  Public Members

  void *ptr

    Pointer to the block data.

  size_t size

    The size of the block.

  bool used

    Block status. True: used, False: free.

### Macros

HEAP_IRAM_ATTR

MALLOC_CAP_EXEC

  Flags to indicate the capabilities of the various memory systems.

  Memory must be able to run executable code

MALLOC_CAP_32BIT

  Memory must allow for aligned 32-bit data accesses.

MALLOC_CAP_8BIT

  Memory must allow for 8/16/...-bit data accesses.

MALLOC_CAP_DMA

  Memory must be able to accessed by DMA.

MALLOC_CAP_PID2

  Memory must be mapped to PID2 memory space (PIDs are not currently used)

MALLOC_CAP_PID3

  Memory must be mapped to PID3 memory space (PIDs are not currently used)

MALLOC_CAP_PID4

  Memory must be mapped to PID4 memory space (PIDs are not currently used)

MALLOC_CAP_PID5

  Memory must be mapped to PID5 memory space (PIDs are not currently used)

MALLOC_CAP_PID6

  Memory must be mapped to PID6 memory space (PIDs are not currently used)

MALLOC_CAP_PID7

  Memory must be mapped to PID7 memory space (PIDs are not currently used)

MALLOC_CAP_SPIRAM

  Memory must be in SPI RAM.

MALLOC_CAP_INTERNAL

  Memory must be internal; specifically it should not disappear when flash/spiram cache is switched off.

MALLOC_CAP_DEFAULT

  Memory can be returned in a non-capability-specific memory allocation (e.g. malloc(), calloc()) call.

MALLOC_CAP_IRAM_8BIT

  Memory must be in IRAM and allow unaligned access.

MALLOC_CAP_RETENTION

  Memory must be able to accessed by retention DMA.

MALLOC_CAP_RTCRAM

  Memory must be in RTC fast memory.

MALLOC_CAP_TCM

  Memory must be in TCM memory.

MALLOC_CAP_DMA_DESC_AHB

  Memory must be capable of containing AHB DMA descriptors.

MALLOC_CAP_DMA_DESC_AXI

  Memory must be capable of containing AXI DMA descriptors.

MALLOC_CAP_CACHE_ALIGNED

  Memory must be aligned to the cache line size of any intermediate caches.

MALLOC_CAP_SIMD

  Memory must be capable of being used for SIMD instructions (i.e. allow for SIMD-specific-bit data accesses)

MALLOC_CAP_INVALID

  Memory can't be used / list end marker.

### Type Definitions

typedef void (*esp_alloc_failed_hook_t)(size_t size, uint32_t caps, const char *function_name)

  callback called when an allocation operation fails, if registered

  Param size:

    in bytes of failed allocation

  Param caps:

    capabilities requested of failed allocation

  Param function_name:

    function which generated the failure

typedef struct walker_heap_info walker_heap_into_t

  Structure used to store heap related data passed to the walker callback function.

typedef struct walker_block_info walker_block_info_t

  Structure used to store block related data passed to the walker callback function.

typedef bool (*heap_caps_walker_cb_t)(walker_heap_into_t heap_info, walker_block_info_t block_info, void *user_data)

  Function callback used to get information of memory block during calls to heap_caps_walk or heap_caps_walk_all.

  Param heap_info:

    See walker_heap_into_t

  Param block_info:

    See walker_block_info_t

  Param user_data:

    Opaque pointer to user defined data

  Return:

    True to proceed with the heap traversal False to stop the traversal of the current heap and continue with the traversal of the next heap (if any)

## API Reference - Initialisation

### Header File

- components/heap/include/esp_heap_caps_init.h

- This header file can be included with:

  >     #include "esp_heap_caps_init.h"

### Functions

void heap_caps_init(void)

  Initialize the capability-aware heap allocator.

  This is called once in the IDF startup code. Do not call it at other times.

void heap_caps_enable_nonos_stack_heaps(void)

  Enable heap(s) in memory regions where the startup stacks are located.

  On startup, the pro/app CPUs have a certain memory region they use as stack, so we cannot do allocations in the regions these stack frames are. When FreeRTOS is completely started, they do not use that memory anymore and heap(s) there can be enabled.

esp_err_t heap_caps_add_region(intptr_t start, intptr_t end)

  Add a region of memory to the collection of heaps at runtime.

  Most memory regions are defined in soc_memory_layout.c for the SoC, and are registered via heap_caps_init(). Some regions can't be used immediately and are later enabled via heap_caps_enable_nonos_stack_heaps().

  Call this function to add a region of memory to the heap at some later time.

  This function does not consider any of the "reserved" regions or other data in soc_memory_layout, caller needs to consider this themselves.

  All memory within the region specified by start & end parameters must be otherwise unused.

  The capabilities of the newly registered memory will be determined by the start address, as looked up in the regions specified in soc_memory_layout.c.

  Use heap_caps_add_region_with_caps() to register a region with custom capabilities.

  Note

  Please refer to following example for memory regions allowed for addition to heap based on an existing region (address range for demonstration purpose only):

            Existing region: 0x1000 <-> 0x3000
            New region:      0x1000 <-> 0x3000 (Allowed)
            New region:      0x1000 <-> 0x2000 (Allowed)
            New region:      0x0000 <-> 0x1000 (Allowed)
            New region:      0x3000 <-> 0x4000 (Allowed)
            New region:      0x0000 <-> 0x2000 (NOT Allowed)
            New region:      0x0000 <-> 0x4000 (NOT Allowed)
            New region:      0x1000 <-> 0x4000 (NOT Allowed)
            New region:      0x2000 <-> 0x4000 (NOT Allowed)

  Parameters:

    - start -- Start address of new region.

    - end -- End address of new region.

  Returns:

    ESP_OK on success, ESP_ERR_INVALID_ARG if a parameter is invalid, ESP_ERR_NOT_FOUND if the specified start address doesn't reside in a known region, or any error returned by heap_caps_add_region_with_caps().

esp_err_t heap_caps_add_region_with_caps(const uint32_t caps[], intptr_t start, intptr_t end)

  Add a region of memory to the collection of heaps at runtime, with custom capabilities.

  Similar to heap_caps_add_region(), only custom memory capabilities are specified by the caller.

  Note

  Please refer to following example for memory regions allowed for addition to heap based on an existing region (address range for demonstration purpose only):

            Existing region: 0x1000 <-> 0x3000
            New region:      0x1000 <-> 0x3000 (Allowed)
            New region:      0x1000 <-> 0x2000 (Allowed)
            New region:      0x0000 <-> 0x1000 (Allowed)
            New region:      0x3000 <-> 0x4000 (Allowed)
            New region:      0x0000 <-> 0x2000 (NOT Allowed)
            New region:      0x0000 <-> 0x4000 (NOT Allowed)
            New region:      0x1000 <-> 0x4000 (NOT Allowed)
            New region:      0x2000 <-> 0x4000 (NOT Allowed)

  Parameters:

    - caps -- Ordered array of capability masks for the new region, in order of priority. Must have length SOC_MEMORY_TYPE_NO_PRIOS. Does not need to remain valid after the call returns.

    - start -- Start address of new region.

    - end -- End address of new region.

  Returns:

    - ESP_OK on success

    - ESP_ERR_INVALID_ARG if a parameter is invalid

    - ESP_ERR_NO_MEM if no memory to register new heap.

    - ESP_ERR_INVALID_SIZE if the memory region is too small to fit a heap

    - ESP_FAIL if region overlaps the start and/or end of an existing region

## API Reference - Multi-Heap API

(Note: The multi-heap API is used internally by the heap capabilities allocator. Most ESP-IDF programs never need to call this API directly.)

### Header File

- components/heap/include/multi_heap.h

- This header file can be included with:

  >     #include "multi_heap.h"

### Functions

void *multi_heap_aligned_alloc(multi_heap_handle_t heap, size_t size, size_t alignment)

  allocate a chunk of memory with specific alignment

  Parameters:

    - heap -- Handle to a registered heap.

    - size -- size in bytes of memory chunk

    - alignment -- how the memory must be aligned

  Returns:

    pointer to the memory allocated, NULL on failure

void *multi_heap_malloc(multi_heap_handle_t heap, size_t size)

  malloc() a buffer in a given heap

  Semantics are the same as standard malloc(), only the returned buffer will be allocated in the specified heap.

  Parameters:

    - heap -- Handle to a registered heap.

    - size -- Size of desired buffer.

  Returns:

    Pointer to new memory, or NULL if allocation fails.

void multi_heap_aligned_free(multi_heap_handle_t heap, void *p)

  free() a buffer aligned in a given heap.

  Note

  This function is deprecated, consider using multi_heap_free() instead

  Parameters:

    - heap -- Handle to a registered heap.

    - p -- NULL, or a pointer previously returned from multi_heap_aligned_alloc() for the same heap.

void multi_heap_free(multi_heap_handle_t heap, void *p)

  free() a buffer in a given heap.

  Semantics are the same as standard free(), only the argument 'p' must be NULL or have been allocated in the specified heap.

  Parameters:

    - heap -- Handle to a registered heap.

    - p -- NULL, or a pointer previously returned from multi_heap_malloc() or multi_heap_realloc() for the same heap.

void *multi_heap_realloc(multi_heap_handle_t heap, void *p, size_t size)

  realloc() a buffer in a given heap.

  Semantics are the same as standard realloc(), only the argument 'p' must be NULL or have been allocated in the specified heap.

  Parameters:

    - heap -- Handle to a registered heap.

    - p -- NULL, or a pointer previously returned from multi_heap_malloc() or multi_heap_realloc() for the same heap.

    - size -- Desired new size for buffer.

  Returns:

    New buffer of 'size' containing contents of 'p', or NULL if reallocation failed.

size_t multi_heap_get_allocated_size(multi_heap_handle_t heap, void *p)

  Return the size that a particular pointer was allocated with.

  Parameters:

    - heap -- Handle to a registered heap.

    - p -- Pointer, must have been previously returned from multi_heap_malloc() or multi_heap_realloc() for the same heap.

  Returns:

    Size of the memory allocated at this block. May be more than the original size argument, due to padding and minimum block sizes.

multi_heap_handle_t multi_heap_register(void *start, size_t size)

  Register a new heap for use.

  This function initialises a heap at the specified address, and returns a handle for future heap operations.

  There is no equivalent function for deregistering a heap - if all blocks in the heap are free, you can immediately start using the memory for other purposes.

  Parameters:

    - start -- Start address of the memory to use for a new heap.

    - size -- Size (in bytes) of the new heap.

  Returns:

    Handle of a new heap ready for use, or NULL if the heap region was too small to be initialised.

void multi_heap_set_lock(multi_heap_handle_t heap, void *lock)

  Associate a private lock pointer with a heap.

  The lock argument is supplied to the MULTI_HEAP_LOCK() and MULTI_HEAP_UNLOCK() macros, defined in multi_heap_platform.h.

  The lock in question must be recursive.

  When the heap is first registered, the associated lock is NULL.

  Parameters:

    - heap -- Handle to a registered heap.

    - lock -- Optional pointer to a locking structure to associate with this heap.

void multi_heap_dump(multi_heap_handle_t heap)

  Dump heap information to stdout.

  For debugging purposes, this function dumps information about every block in the heap to stdout.

  Parameters:

    heap -- Handle to a registered heap.

bool multi_heap_check(multi_heap_handle_t heap, bool print_errors)

  Check heap integrity.

  Walks the heap and checks all heap data structures are valid. If any errors are detected, an error-specific message can be optionally printed to stderr. Print behaviour can be overridden at compile time by defining MULTI_CHECK_FAIL_PRINTF in multi_heap_platform.h.

  Note

  This function is not thread-safe as it sets a global variable with the value of print_errors.

  Parameters:

    - heap -- Handle to a registered heap.

    - print_errors -- If true, errors will be printed to stderr.

  Returns:

    true if heap is valid, false otherwise.

size_t multi_heap_free_size(multi_heap_handle_t heap)

  Return free heap size.

  Returns the number of bytes available in the heap.

  Equivalent to the total_free_bytes member returned by multi_heap_get_heap_info().

  Note that the heap may be fragmented, so the actual maximum size for a single malloc() may be lower. To know this size, see the largest_free_block member returned by multi_heap_get_heap_info().

  Parameters:

    heap -- Handle to a registered heap.

  Returns:

    Number of free bytes.

size_t multi_heap_minimum_free_size(multi_heap_handle_t heap)

  Return the lifetime minimum free heap size.

  Equivalent to the minimum_free_bytes member returned by multi_heap_get_info().

  Returns the lifetime "low watermark" of possible values returned from multi_free_heap_size(), for the specified heap.

  Parameters:

    heap -- Handle to a registered heap.

  Returns:

    Number of free bytes.

void multi_heap_get_info(multi_heap_handle_t heap, multi_heap_info_t *info)

  Return metadata about a given heap.

  Fills a multi_heap_info_t structure with information about the specified heap.

  Parameters:

    - heap -- Handle to a registered heap.

    - info -- Pointer to a structure to fill with heap metadata.

void *multi_heap_aligned_alloc_offs(multi_heap_handle_t heap, size_t size, size_t alignment, size_t offset)

  Perform an aligned allocation from the provided offset.

  Parameters:

    - heap -- The heap in which to perform the allocation

    - size -- The size of the allocation

    - alignment -- How the memory must be aligned

    - offset -- The offset at which the alignment should start

  Returns:

    void* The ptr to the allocated memory

size_t multi_heap_reset_minimum_free_bytes(multi_heap_handle_t heap)

  Reset the minimum_free_bytes value (setting it to free_bytes) and return the former value.

  Parameters:

    heap -- The heap in which the reset is taking place

  Returns:

    size_t the value of minimum_free_bytes before it is reset

void multi_heap_restore_minimum_free_bytes(multi_heap_handle_t heap, const size_t new_minimum_free_bytes_value)

  Set the value of minimum_free_bytes to new_minimum_free_bytes_value or keep the current value of minimum_free_bytes if it is smaller than new_minimum_free_bytes_value.

  Parameters:

    - heap -- The heap in which the restore is taking place

    - new_minimum_free_bytes_value -- The value to restore the minimum_free_bytes to

void multi_heap_walk(multi_heap_handle_t heap, multi_heap_walker_cb_t walker_func, void *user_data)

  Call the tlsf_walk_pool function of the heap given as parameter with the walker function passed as parameter.

  Parameters:

    - heap -- The heap to traverse

    - walker_func -- The walker to trigger on each block of the heap

    - user_data -- Opaque pointer to user defined data

### Structures

struct multi_heap_info_t

  Structure to access heap metadata via multi_heap_get_info.

  Public Members

  size_t total_free_bytes

    Total free bytes in the heap. Equivalent to multi_free_heap_size().

  size_t total_allocated_bytes

    Total bytes allocated to data in the heap.

  size_t largest_free_block

    Size of the largest free block in the heap. This is the largest malloc-able size.

  size_t minimum_free_bytes

    Lifetime minimum free heap size. Equivalent to multi_minimum_free_heap_size().

  size_t allocated_blocks

    Number of (variable size) blocks allocated in the heap.

  size_t free_blocks

    Number of (variable size) free blocks in the heap.

  size_t total_blocks

    Total number of (variable size) blocks in the heap.

### Type Definitions

typedef struct multi_heap_info *multi_heap_handle_t

  Opaque handle to a registered heap.

typedef bool (*multi_heap_walker_cb_t)(void *block_ptr, size_t block_size, int block_used, void *user_data)

  Callback called when walking the given heap blocks of memory.

  Param block_ptr:

    Pointer to the block data

  Param block_size:

    The size of the block

  Param block_used:

    Block status. 0: free, 1: allocated

  Param user_data:

    Opaque pointer to user defined data

  Return:

    True if the walker is expected to continue the heap traversal False if the walker is expected to stop the traversal of the heap

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