简介
非易失性存储 (NVS) 库主要用于在 flash 中存储键值格式的数据。
底层存储
NVS 通过调用 spi_flash_{read|write|erase} API 对主 flash 的部分空间进行读、写、擦除操作，包括 data 类型和 nvs 子类型的所有分区。应用程序可调用 nvs_open API 选择使用带有 nvs 标签的分区，也可以通过调用 nvs_open_from_part API 选择使用指定名称的任意分区。
键值对
NVS 的操作对象为键值对，其中键是 ASCII 字符串，当前支持最大键长为 15 个字符，值可以为以下几种类型：
◍ 整数型：uint8_t、int8_t、uint16_t、int16_t、uint32_t、int32_t、uint64_t 和 int64_t；
◍ 以 \0 结尾的字符串；
◍ 可变长度的二进制数据 (BLOB)
*注：字符串值当前上限为 4000 字节，其中包括空终止符。BLOB 值上限为 508,000 字节或分区大小减去 4000 字节的 97.6%，以较低值为准。
键必须唯一。为现有的键写入新的值可能产生如下结果：
◍ 如果新旧值数据类型相同，则更新值；
◍ 如果新旧值数据类型不同，则返回错误。
读取值时也会执行数据类型检查。如果读取操作的数据类型与该值的数据类型不匹配，则返回错误。
NVS 优势
1、接口更加安全: NVS 不直接操作 address. 对于终端用户而已, 更加安全。
2、接口使用接近用户习惯，NVS 接口类似于电脑上操作文件一样:
打开文件(nvs_open), 写文件(nvs_set_xxx), 保存文件(nvs_commit), 关闭文件(nvs_close)
打开文件(nvs_open), 读取文件(nvs_get_xxx), 关闭文件(nvs_close)
3、擦写均衡, 使 flash 寿命更长，NVS 在操作少量数据上, NVS 分区更大时, 擦写均衡表现的更为明显。
API 分析参考
初始化
/**
* @brief Initialize the default NVS partition.
*
* This API initialises the default NVS partition. The default NVS partition
* is the one that is labeled "nvs" in the partition table.
*
* @return
* - ESP_OK if storage was successfully initialized.
* - ESP_ERR_NVS_NO_FREE_PAGES if the NVS storage contains no empty pages
* (which may happen if NVS partition was truncated)
* - ESP_ERR_NOT_FOUND if no partition with label "nvs" is found in the partition table
* - one of the error codes from the underlying flash storage driver
*/
esp_err_t nvs_flash_init(void);
/**
* @brief Initialize NVS flash storage for the specified partition.
*
* @param[in] partition_label Label of the partition. Note that internally a reference to
* passed value is kept and it should be accessible for future operations
*
* @return
* - ESP_OK if storage was successfully initialized.
* - ESP_ERR_NVS_NO_FREE_PAGES if the NVS storage contains no empty pages
* (which may happen if NVS partition was truncated)
* - ESP_ERR_NOT_FOUND if specified partition is not found in the partition table
* - one of the error codes from the underlying flash storage driver
*/
esp_err_t nvs_flash_init_partition(const char *partition_label);
擦除
/**
* @brief Erase the default NVS partition
*
* This function erases all contents of the default NVS partition (one with label "nvs")
*
* @return
* - ESP_OK on success
* - ESP_ERR_NOT_FOUND if there is no NVS partition labeled "nvs" in the
* partition table
*/
esp_err_t nvs_flash_erase(void);
/**
* @brief Erase specified NVS partition
*
* This function erases all contents of specified NVS partition
*
* @param[in] part_name Name (label) of the partition to be erased
*
* @return
* - ESP_OK on success
* - ESP_ERR_NOT_FOUND if there is no NVS partition with the specified name
* in the partition table
*/
esp_err_t nvs_flash_erase_partition(const char *part_name);
打开文件
/**
* @brief Open non-volatile storage with a given namespace from the default NVS partition
*
* Multiple internal ESP-IDF and third party application modules can store
* their key-value pairs in the NVS module. In order to reduce possible
* conflicts on key names, each module can use its own namespace.
* The default NVS partition is the one that is labelled "nvs" in the partition
* table.
*
* @param[in] name Namespace name. Maximal length is determined by the
* underlying implementation, but is guaranteed to be
* at least 15 characters. Shouldn't be empty.
* @param[in] open_mode NVS_READWRITE or NVS_READONLY. If NVS_READONLY, will
* open a handle for reading only. All write requests will
* be rejected for this handle.
* @param[out] out_handle If successful (return code is zero), handle will be
* returned in this argument.
*
* @return
* - ESP_OK if storage handle was opened successfully
* - ESP_ERR_NVS_NOT_INITIALIZED if the storage driver is not initialized
* - ESP_ERR_NVS_PART_NOT_FOUND if the partition with label "nvs" is not found
* - ESP_ERR_NVS_NOT_FOUND id namespace doesn't exist yet and
* mode is NVS_READONLY
* - ESP_ERR_NVS_INVALID_NAME if namespace name doesn't satisfy constraints
* - other error codes from the underlying storage driver
*/
esp_err_t nvs_open(const char* name, nvs_open_mode open_mode, nvs_handle *out_handle);
/**
* @brief Open non-volatile storage with a given namespace from specified partition
*
* The behaviour is same as nvs_open() API. However this API can operate on a specified NVS
* partition instead of default NVS partition. Note that the specified partition must be registered
* with NVS using nvs_flash_init_partition() API.
*
* @param[in] part_name Label (name) of the partition of interest for object read/write/erase
* @param[in] name Namespace name. Maximal length is determined by the
* underlying implementation, but is guaranteed to be
* at least 15 characters. Shouldn't be empty.
* @param[in] open_mode NVS_READWRITE or NVS_READONLY. If NVS_READONLY, will
* open a handle for reading only. All write requests will
* be rejected for this handle.
* @param[out] out_handle If successful (return code is zero), handle will be
* returned in this argument.
*
* @return
* - ESP_OK if storage handle was opened successfully
* - ESP_ERR_NVS_NOT_INITIALIZED if the storage driver is not initialized
* - ESP_ERR_NVS_PART_NOT_FOUND if the partition with specified name is not found
* - ESP_ERR_NVS_NOT_FOUND id namespace doesn't exist yet and
* mode is NVS_READONLY
* - ESP_ERR_NVS_INVALID_NAME if namespace name doesn't satisfy constraints
* - other error codes from the underlying storage driver
*/
esp_err_t nvs_open_from_partition(const char *part_name, const char* name, nvs_open_mode open_mode, nvs_handle *out_handle);
数据写入
/**@{*/
/**
* @brief set value for given key
*
* This family of functions set value for the key, given its name. Note that
* actual storage will not be updated until nvs_commit function is called.
*
* @param[in] handle Handle obtained from nvs_open function.
* Handles that were opened read only cannot be used.
* @param[in] key Key name. Maximal length is determined by the underlying
* implementation, but is guaranteed to be at least
* 15 characters. Shouldn't be empty.
* @param[in] value The value to set.
* For strings, the maximum length (including null character) is
* 4000 bytes.
*
* @return
* - ESP_OK if value was set successfully
* - ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
* - ESP_ERR_NVS_READ_ONLY if storage handle was opened as read only
* - ESP_ERR_NVS_INVALID_NAME if key name doesn't satisfy constraints
* - ESP_ERR_NVS_NOT_ENOUGH_SPACE if there is not enough space in the
* underlying storage to save the value
* - ESP_ERR_NVS_REMOVE_FAILED if the value wasn't updated because flash
* write operation has failed. The value was written however, and
* update will be finished after re-initialization of nvs, provided that
* flash operation doesn't fail again.
* - ESP_ERR_NVS_VALUE_TOO_LONG if the string value is too long
*/
esp_err_t nvs_set_i8 (nvs_handle handle, const char* key, int8_t value);
esp_err_t nvs_set_u8 (nvs_handle handle, const char* key, uint8_t value);
esp_err_t nvs_set_i16 (nvs_handle handle, const char* key, int16_t value);
esp_err_t nvs_set_u16 (nvs_handle handle, const char* key, uint16_t value);
esp_err_t nvs_set_i32 (nvs_handle handle, const char* key, int32_t value);
esp_err_t nvs_set_u32 (nvs_handle handle, const char* key, uint32_t value);
esp_err_t nvs_set_i64 (nvs_handle handle, const char* key, int64_t value);
esp_err_t nvs_set_u64 (nvs_handle handle, const char* key, uint64_t value);
esp_err_t nvs_set_str (nvs_handle handle, const char* key, const char* value);
/**@}*/
/**
* @brief set variable length binary value for given key
*
* This family of functions set value for the key, given its name. Note that
* actual storage will not be updated until nvs_commit function is called.
*
* @param[in] handle Handle obtained from nvs_open function.
* Handles that were opened read only cannot be used.
* @param[in] key Key name. Maximal length is 15 characters. Shouldn't be empty.
* @param[in] value The value to set.
* @param[in] length length of binary value to set, in bytes; Maximum length is
* 508000 bytes or (97.6% of the partition size - 4000) bytes
* whichever is lower.
*
* @return
* - ESP_OK if value was set successfully
* - ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
* - ESP_ERR_NVS_READ_ONLY if storage handle was opened as read only
* - ESP_ERR_NVS_INVALID_NAME if key name doesn't satisfy constraints
* - ESP_ERR_NVS_NOT_ENOUGH_SPACE if there is not enough space in the
* underlying storage to save the value
* - ESP_ERR_NVS_REMOVE_FAILED if the value wasn't updated because flash
* write operation has failed. The value was written however, and
* update will be finished after re-initialization of nvs, provided that
* flash operation doesn't fail again.
* - ESP_ERR_NVS_VALUE_TOO_LONG if the value is too long
*/
esp_err_t nvs_set_blob(nvs_handle handle, const char* key, const void* value, size_t length);
数据读出
/**@{*/
/**
* @brief get value for given key
*
* These functions retrieve value for the key, given its name. If key does not
* exist, or the requested variable type doesn't match the type which was used
* when setting a value, an error is returned.
*
* In case of any error, out_value is not modified.
*
* All functions expect out_value to be a pointer to an already allocated variable
* of the given type.
*
* \code{c}
* // Example of using nvs_get_i32:
* int32_t max_buffer_size = 4096; // default value
* esp_err_t err = nvs_get_i32(my_handle, "max_buffer_size", &max_buffer_size);
* assert(err == ESP_OK || err == ESP_ERR_NVS_NOT_FOUND);
* // if ESP_ERR_NVS_NOT_FOUND was returned, max_buffer_size will still
* // have its default value.
*
* \endcode
*
* @param[in] handle Handle obtained from nvs_open function.
* @param[in] key Key name. Maximal length is determined by the underlying
* implementation, but is guaranteed to be at least
* 15 characters. Shouldn't be empty.
* @param out_value Pointer to the output value.
* May be NULL for nvs_get_str and nvs_get_blob, in this
* case required length will be returned in length argument.
*
* @return
* - ESP_OK if the value was retrieved successfully
* - ESP_ERR_NVS_NOT_FOUND if the requested key doesn't exist
* - ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
* - ESP_ERR_NVS_INVALID_NAME if key name doesn't satisfy constraints
* - ESP_ERR_NVS_INVALID_LENGTH if length is not sufficient to store data
*/
esp_err_t nvs_get_i8 (nvs_handle handle, const char* key, int8_t* out_value);
esp_err_t nvs_get_u8 (nvs_handle handle, const char* key, uint8_t* out_value);
esp_err_t nvs_get_i16 (nvs_handle handle, const char* key, int16_t* out_value);
esp_err_t nvs_get_u16 (nvs_handle handle, const char* key, uint16_t* out_value);
esp_err_t nvs_get_i32 (nvs_handle handle, const char* key, int32_t* out_value);
esp_err_t nvs_get_u32 (nvs_handle handle, const char* key, uint32_t* out_value);
esp_err_t nvs_get_i64 (nvs_handle handle, const char* key, int64_t* out_value);
esp_err_t nvs_get_u64 (nvs_handle handle, const char* key, uint64_t* out_value);
/**@}*/
/**
* @brief get value for given key
*
* These functions retrieve value for the key, given its name. If key does not
* exist, or the requested variable type doesn't match the type which was used
* when setting a value, an error is returned.
*
* In case of any error, out_value is not modified.
*
* All functions expect out_value to be a pointer to an already allocated variable
* of the given type.
*
* nvs_get_str and nvs_get_blob functions support WinAPI-style length queries.
* To get the size necessary to store the value, call nvs_get_str or nvs_get_blob
* with zero out_value and non-zero pointer to length. Variable pointed to
* by length argument will be set to the required length. For nvs_get_str,
* this length includes the zero terminator. When calling nvs_get_str and
* nvs_get_blob with non-zero out_value, length has to be non-zero and has to
* point to the length available in out_value.
* It is suggested that nvs_get/set_str is used for zero-terminated C strings, and
* nvs_get/set_blob used for arbitrary data structures.
*
* \code{c}
* // Example (without error checking) of using nvs_get_str to get a string into dynamic array:
* size_t required_size;
* nvs_get_str(my_handle, "server_name", NULL, &required_size);
* char* server_name = malloc(required_size);
* nvs_get_str(my_handle, "server_name", server_name, &required_size);
*
* // Example (without error checking) of using nvs_get_blob to get a binary data
* into a static array:
* uint8_t mac_addr[6];
* size_t size = sizeof(mac_addr);
* nvs_get_blob(my_handle, "dst_mac_addr", mac_addr, &size);
* \endcode
*
* @param[in] handle Handle obtained from nvs_open function.
* @param[in] key Key name. Maximal length is determined by the underlying
* implementation, but is guaranteed to be at least
* 15 characters. Shouldn't be empty.
* @param out_value Pointer to the output value.
* May be NULL for nvs_get_str and nvs_get_blob, in this
* case required length will be returned in length argument.
* @param[inout] length A non-zero pointer to the variable holding the length of out_value.
* In case out_value a zero, will be set to the length
* required to hold the value. In case out_value is not
* zero, will be set to the actual length of the value
* written. For nvs_get_str this includes zero terminator.
*
* @return
* - ESP_OK if the value was retrieved successfully
* - ESP_ERR_NVS_NOT_FOUND if the requested key doesn't exist
* - ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
* - ESP_ERR_NVS_INVALID_NAME if key name doesn't satisfy constraints
* - ESP_ERR_NVS_INVALID_LENGTH if length is not sufficient to store data
*/
/**@{*/
esp_err_t nvs_get_str (nvs_handle handle, const char* key, char* out_value, size_t* length);
esp_err_t nvs_get_blob(nvs_handle handle, const char* key, void* out_value, size_t* length);
提交保存数据
/**
* @brief Write any pending changes to non-volatile storage
*
* After setting any values, nvs_commit() must be called to ensure changes are written
* to non-volatile storage. Individual implementations may write to storage at other times,
* but this is not guaranteed.
*
* @param[in] handle Storage handle obtained with nvs_open.
* Handles that were opened read only cannot be used.
*
* @return
* - ESP_OK if the changes have been written successfully
* - ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
* - other error codes from the underlying storage driver
*/
esp_err_t nvs_commit(nvs_handle handle);
不透明句柄
/**
* Opaque pointer type representing non-volatile storage handle
*/
typedef uint32_t nvs_handle;
#define ESP_ERR_NVS_BASE 0x1100 /*!< Starting number of error codes */
#define ESP_ERR_NVS_NOT_INITIALIZED (ESP_ERR_NVS_BASE + 0x01) /*!< The storage driver is not initialized */
#define ESP_ERR_NVS_NOT_FOUND (ESP_ERR_NVS_BASE + 0x02) /*!< Id namespace doesn鈥檛 exist yet and mode is NVS_READONLY */
#define ESP_ERR_NVS_TYPE_MISMATCH (ESP_ERR_NVS_BASE + 0x03) /*!< The type of set or get operation doesn't match the type of value stored in NVS */
#define ESP_ERR_NVS_READ_ONLY (ESP_ERR_NVS_BASE + 0x04) /*!< Storage handle was opened as read only */
#define ESP_ERR_NVS_NOT_ENOUGH_SPACE (ESP_ERR_NVS_BASE + 0x05) /*!< There is not enough space in the underlying storage to save the value */
#define ESP_ERR_NVS_INVALID_NAME (ESP_ERR_NVS_BASE + 0x06) /*!< Namespace name doesn鈥檛 satisfy constraints */
#define ESP_ERR_NVS_INVALID_HANDLE (ESP_ERR_NVS_BASE + 0x07) /*!< Handle has been closed or is NULL */
#define ESP_ERR_NVS_REMOVE_FAILED (ESP_ERR_NVS_BASE + 0x08) /*!< The value wasn鈥檛 updated because flash write operation has failed. The value was written however, and update will be finished after re-initialization of nvs, provided that flash operation doesn鈥檛 fail again. */
#define ESP_ERR_NVS_KEY_TOO_LONG (ESP_ERR_NVS_BASE + 0x09) /*!< Key name is too long */
#define ESP_ERR_NVS_PAGE_FULL (ESP_ERR_NVS_BASE + 0x0a) /*!< Internal error; never returned by nvs API functions */
#define ESP_ERR_NVS_INVALID_STATE (ESP_ERR_NVS_BASE + 0x0b) /*!< NVS is in an inconsistent state due to a previous error. Call nvs_flash_init and nvs_open again, then retry. */
#define ESP_ERR_NVS_INVALID_LENGTH (ESP_ERR_NVS_BASE + 0x0c) /*!< String or blob length is not sufficient to store data */
#define ESP_ERR_NVS_NO_FREE_PAGES (ESP_ERR_NVS_BASE + 0x0d) /*!< NVS partition doesn't contain any empty pages. This may happen if NVS partition was truncated. Erase the whole partition and call nvs_flash_init again. */
#define ESP_ERR_NVS_VALUE_TOO_LONG (ESP_ERR_NVS_BASE + 0x0e) /*!< String or blob length is longer than supported by the implementation */
#define ESP_ERR_NVS_PART_NOT_FOUND (ESP_ERR_NVS_BASE + 0x0f) /*!< Partition with specified name is not found in the partition table */
#define ESP_ERR_NVS_NEW_VERSION_FOUND (ESP_ERR_NVS_BASE + 0x10) /*!< NVS partition contains data in new format and cannot be recognized by this version of code */
#define ESP_ERR_NVS_XTS_ENCR_FAILED (ESP_ERR_NVS_BASE + 0x11) /*!< XTS encryption failed while writing NVS entry */
#define ESP_ERR_NVS_XTS_DECR_FAILED (ESP_ERR_NVS_BASE + 0x12) /*!< XTS decryption failed while reading NVS entry */
#define ESP_ERR_NVS_XTS_CFG_FAILED (ESP_ERR_NVS_BASE + 0x13) /*!< XTS configuration setting failed */
#define ESP_ERR_NVS_XTS_CFG_NOT_FOUND (ESP_ERR_NVS_BASE + 0x14) /*!< XTS configuration not found */
#define ESP_ERR_NVS_ENCR_NOT_SUPPORTED (ESP_ERR_NVS_BASE + 0x15) /*!< NVS encryption is not supported in this version */
#define ESP_ERR_NVS_KEYS_NOT_INITIALIZED (ESP_ERR_NVS_BASE + 0x16) /*!< NVS key partition is uninitialized */
#define ESP_ERR_NVS_CORRUPT_KEY_PART (ESP_ERR_NVS_BASE + 0x17) /*!< NVS key partition is corrupt */
例子（保存系统重启次数）：
#include <Arduino.h>
#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_system.h"
#include "nvs_flash.h"
#include "nvs.h"
void setup()
{
Serial.begin(9600);
// 初始化NVS
esp_err_t err = nvs_flash_init();
if (err == ESP_ERR_NVS_NO_FREE_PAGES || err == ESP_ERR_NVS_NEW_VERSION_FOUND) {
// NVS partition was truncated and needs to be erased
// Retry nvs_flash_init
ESP_ERROR_CHECK(nvs_flash_erase());
err = nvs_flash_init();
}
ESP_ERROR_CHECK( err );
// Open
printf("\n");
printf("Opening Non-Volatile Storage (NVS) handle... ");
nvs_handle_t my_handle;
err = nvs_open("storage", NVS_READWRITE, &my_handle);
if (err != ESP_OK) {
printf("Error (%s) opening NVS handle!\n", esp_err_to_name(err));
} else {
printf("Done\n");
// Read
printf("Reading restart counter from NVS ... ");
int32_t restart_counter = 0; // value will default to 0, if not set yet in NVS
err = nvs_get_i32(my_handle, "restart_counter", &restart_counter);
switch (err) {
case ESP_OK:
printf("Done\n");
printf("Restart counter = %d\n", restart_counter);
break;
case ESP_ERR_NVS_NOT_FOUND:
printf("The value is not initialized yet!\n");
break;
default :
printf("Error (%s) reading!\n", esp_err_to_name(err));
}
// Write
printf("Updating restart counter in NVS ... ");
restart_counter++;
err = nvs_set_i32(my_handle, "restart_counter", restart_counter);
printf((err != ESP_OK) ? "Failed!\n" : "Done\n");
// Commit written value.
// After setting any values, nvs_commit() must be called to ensure changes are written
// to flash storage. Implementations may write to storage at other times,
// but this is not guaranteed.
printf("Committing updates in NVS ... ");
err = nvs_commit(my_handle);
printf((err != ESP_OK) ? "Failed!\n" : "Done\n");
// Close
nvs_close(my_handle);
}
printf("\n");
// Restart module
for (int i = 10; i >= 0; i--) {
printf("Restarting in %d seconds...\n", i);
vTaskDelay(1000 / portTICK_PERIOD_MS);
}
printf("Restarting now.\n");
fflush(stdout);
esp_restart();
}
void loop()
{
80 delay(0xFFFFFF);
}
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