ESP-NOW

[English]

概述

ESP-NOW 是一种由乐鑫公司定义的无连接 Wi-Fi 通信协议。在 ESP-NOW 中,应用程序数据被封装在各个供应商的动作帧中,然后在无连接的情况下,从一个 Wi-Fi 设备传输到另一个 Wi-Fi 设备。

CTR 与 CBC-MAC 协议 (CCMP) 可用来保护动作帧的安全。ESP-NOW 广泛应用于智能照明、远程控制、传感器等领域。

帧格式

ESP-NOW 使用各个供应商的动作帧传输数据,默认比特率为 1 Mbps。各个供应商的动作帧格式为:

-----------------------------------------------------------------------------------------
|   MAC 报头   |  分类代码  |  组织标识符  |  随机值  |  供应商特定内容  |   FCS   |
-----------------------------------------------------------------------------------------
   24 字节        1 字节        3 字节      4 字节      7-257 字节       4 字节
  • 分类代码:分类代码字段可用于指示各个供应商的类别(比如 127)。

  • 组织标识符:组织标识符包含一个唯一标识符(比如 0x18fe34),为乐鑫指定的 MAC 地址的前三个字节。

  • 随机值:防止重放攻击。

  • 供应商特定内容:供应商特定内容包含供应商特定字段,如下所示:

----------------------------------------------------------------------------------------
|  元素 ID  |  长度  |  组织标识符  |  类型  |  版本  |     正文     |
----------------------------------------------------------------------------------------
   1 字节     1 字节     3 字节      1 字节   1 字节    0-250 字节
  • 元素 ID:元素 ID 字段可用于指示特定于供应商的元素。

  • 长度:长度是组织标识符、类型、版本和正文的总长度。

  • 组织标识符:组织标识符包含一个唯一标识符(比如 0x18fe34),为乐鑫指定的 MAC 地址的前三个字节。

  • 类型:类型字段设置为 4,代表 ESP-NOW。

  • 版本:版本字段设置为 ESP-NOW 的版本。

  • 正文:正文包含 ESP-NOW 数据。

由于 ESP-NOW 是无连接的,因此 MAC 报头与标准帧略有不同。FrameControl 字段的 FromDS 和 ToDS 位均为 0。第一个地址字段用于配置目标地址。第二个地址字段用于配置源地址。第三个地址字段用于配置广播地址 (0xff:0xff:0xff:0xff:0xff:0xff)。

安全

ESP-NOW 采用 CCMP 方法保护供应商特定动作帧的安全,具体可参考 IEEE Std. 802.11-2012。Wi-Fi 设备维护一个初始主密钥 (PMK) 和若干本地主密钥 (LMKs,每个配对设备拥有一个 LMK),长度均为 16 个字节。

  • PMK 可使用 AES-128 算法加密 LMK。请调用 esp_now_set_pmk() 设置 PMK。如果未设置 PMK,将使用默认 PMK。

  • LMK 可通过 CCMP 方法对供应商特定的动作帧进行加密。如果未设置配对设备的 LMK,则动作帧不进行加密。

目前,不支持加密组播供应商特定的动作帧。

初始化和反初始化

调用 esp_now_init() 初始化 ESP-NOW,调用 esp_now_deinit() 反初始化 ESP-NOW。ESP-NOW 数据必须在 Wi-Fi 启动后传输,因此建议在初始化 ESP-NOW 之前启动 Wi-Fi,并在反初始化 ESP-NOW 之后停止 Wi-Fi。

当调用 esp_now_deinit() 时,配对设备的所有信息都将被删除。

添加配对设备

在将数据发送到其他设备之前,请先调用 esp_now_add_peer() 将其添加到配对设备列表中。如果启用了加密,则必须设置 LMK。ESP-NOW 数据可以从 Station 或 SoftAP 接口发送。确保在发送 ESP-NOW 数据之前已启用该接口。

配对设备的最大数量是 20,其中加密设备的数量不超过 17,默认值是 7。如果想要修改加密设备的数量,在 Wi-Fi menuconfig 设置 CONFIG_ESP_WIFI_ESPNOW_MAX_ENCRYPT_NUM

在发送广播数据之前必须添加具有广播 MAC 地址的设备。配对设备的信道范围是从 0 ~ 14。如果信道设置为 0,数据将在当前信道上发送。否则,必须使用本地设备所在的通道。

发送 ESP-NOW 数据

调用 esp_now_send() 发送 ESP-NOW 数据,调用 esp_now_register_send_cb() 注册发送回调函数。如果 MAC 层成功接收到数据,则该函数将返回 ESP_NOW_SEND_SUCCESS 事件。否则,它将返回 ESP_NOW_SEND_FAIL。ESP-NOW 数据发送失败可能有几种原因,比如目标设备不存在、设备的信道不相同、动作帧在传输过程中丢失等。应用层并不一定可以总能接收到数据。如果需要,应用层可在接收 ESP-NOW 数据时发回一个应答 (ACK) 数据。如果接收 ACK 数据超时,则将重新传输 ESP-NOW 数据。可以为 ESP-NOW 数据设置序列号,从而删除重复的数据。

如果有大量 ESP-NOW 数据要发送,调用 esp_now_send() 时需注意单次发送的数据不能超过 250 字节。请注意,两个 ESP-NOW 数据包的发送间隔太短可能导致回调函数返回混乱。因此,建议在等到上一次回调函数返回 ACK 后再发送下一个 ESP-NOW 数据。发送回调函数从高优先级的 Wi-Fi 任务中运行。因此,不要在回调函数中执行冗长的操作。相反,将必要的数据发布到队列,并交给优先级较低的任务处理。

接收 ESP-NOW 数据

调用 esp_now_register_recv_cb() 注册接收回调函数。当接收 ESP-NOW 数据时,需要调用接收回调函数。接收回调函数也在 Wi-Fi 任务任务中运行。因此,不要在回调函数中执行冗长的操作。 相反,将必要的数据发布到队列,并交给优先级较低的任务处理。

配置 ESP-NOW 速率

调用 esp_wifi_config_espnow_rate() 配置指定接口的 ESP-NOW 速率。确保在配置速率之前启用接口。这个 API 应该在 esp_wifi_start() 之后调用。

配置 ESP-NOW 功耗参数

当且仅当 ESP32-C3 配置为 STA 模式时,允许其进行休眠。

进行休眠时,调用 esp_now_set_wake_window() 为 ESP-NOW 收包配置 Window。默认情况下 Window 为最大值,将允许一直收包。

如果对 ESP-NOW 进功耗管理,也需要调用 esp_wifi_connectionless_module_set_wake_interval()

请参考 非连接模块功耗管理 获取更多信息。

应用示例

API 参考

Header File

  • components/esp_wifi/include/esp_now.h

  • This header file can be included with:

    #include "esp_now.h"
    
  • This header file is a part of the API provided by the esp_wifi component. To declare that your component depends on esp_wifi, add the following to your CMakeLists.txt:

    REQUIRES esp_wifi
    

    or

    PRIV_REQUIRES esp_wifi
    

Functions

esp_err_t esp_now_init(void)

Initialize ESPNOW function.

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_INTERNAL : Internal error

esp_err_t esp_now_deinit(void)

De-initialize ESPNOW function.

返回

  • ESP_OK : succeed

esp_err_t esp_now_get_version(uint32_t *version)

Get the version of ESPNOW.

参数

version -- ESPNOW version

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_ARG : invalid argument

esp_err_t esp_now_register_recv_cb(esp_now_recv_cb_t cb)

Register callback function of receiving ESPNOW data.

参数

cb -- callback function of receiving ESPNOW data

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

  • ESP_ERR_ESPNOW_INTERNAL : internal error

esp_err_t esp_now_unregister_recv_cb(void)

Unregister callback function of receiving ESPNOW data.

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

esp_err_t esp_now_register_send_cb(esp_now_send_cb_t cb)

Register callback function of sending ESPNOW data.

参数

cb -- callback function of sending ESPNOW data

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

  • ESP_ERR_ESPNOW_INTERNAL : internal error

esp_err_t esp_now_unregister_send_cb(void)

Unregister callback function of sending ESPNOW data.

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

esp_err_t esp_now_send(const uint8_t *peer_addr, const uint8_t *data, size_t len)

Send ESPNOW data.

Attention

1. If peer_addr is not NULL, send data to the peer whose MAC address matches peer_addr

Attention

2. If peer_addr is NULL, send data to all of the peers that are added to the peer list

Attention

3. The maximum length of data must be less than ESP_NOW_MAX_DATA_LEN

Attention

4. The buffer pointed to by data argument does not need to be valid after esp_now_send returns

参数
  • peer_addr -- peer MAC address

  • data -- data to send

  • len -- length of data

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

  • ESP_ERR_ESPNOW_ARG : invalid argument

  • ESP_ERR_ESPNOW_INTERNAL : internal error

  • ESP_ERR_ESPNOW_NO_MEM : out of memory, when this happens, you can delay a while before sending the next data

  • ESP_ERR_ESPNOW_NOT_FOUND : peer is not found

  • ESP_ERR_ESPNOW_IF : current Wi-Fi interface doesn't match that of peer

  • ESP_ERR_ESPNOW_CHAN: current Wi-Fi channel doesn't match that of peer

esp_err_t esp_now_add_peer(const esp_now_peer_info_t *peer)

Add a peer to peer list.

参数

peer -- peer information

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

  • ESP_ERR_ESPNOW_ARG : invalid argument

  • ESP_ERR_ESPNOW_FULL : peer list is full

  • ESP_ERR_ESPNOW_NO_MEM : out of memory

  • ESP_ERR_ESPNOW_EXIST : peer has existed

esp_err_t esp_now_del_peer(const uint8_t *peer_addr)

Delete a peer from peer list.

参数

peer_addr -- peer MAC address

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

  • ESP_ERR_ESPNOW_ARG : invalid argument

  • ESP_ERR_ESPNOW_NOT_FOUND : peer is not found

esp_err_t esp_now_mod_peer(const esp_now_peer_info_t *peer)

Modify a peer.

参数

peer -- peer information

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

  • ESP_ERR_ESPNOW_ARG : invalid argument

  • ESP_ERR_ESPNOW_FULL : peer list is full

esp_err_t esp_wifi_config_espnow_rate(wifi_interface_t ifx, wifi_phy_rate_t rate)

Config ESPNOW rate of specified interface.

Deprecated:

please use esp_now_set_peer_rate_config() instead.

Attention

1. This API should be called after esp_wifi_start().

Attention

2. This API only work when not use Wi-Fi 6 and esp_now_set_peer_rate_config() not called.

参数
  • ifx -- Interface to be configured.

  • rate -- Phy rate to be configured.

返回

  • ESP_OK: succeed

  • others: failed

esp_err_t esp_now_set_peer_rate_config(const uint8_t *peer_addr, esp_now_rate_config_t *config)

Set ESPNOW rate config for each peer.

Attention

1. This API should be called after esp_wifi_start() and esp_now_init().

参数
  • peer_addr -- peer MAC address

  • config -- rate config to be configured.

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

  • ESP_ERR_ESPNOW_ARG : invalid argument

  • ESP_ERR_ESPNOW_INTERNAL : internal error

esp_err_t esp_now_get_peer(const uint8_t *peer_addr, esp_now_peer_info_t *peer)

Get a peer whose MAC address matches peer_addr from peer list.

参数
  • peer_addr -- peer MAC address

  • peer -- peer information

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

  • ESP_ERR_ESPNOW_ARG : invalid argument

  • ESP_ERR_ESPNOW_NOT_FOUND : peer is not found

esp_err_t esp_now_fetch_peer(bool from_head, esp_now_peer_info_t *peer)

Fetch a peer from peer list. Only return the peer which address is unicast, for the multicast/broadcast address, the function will ignore and try to find the next in the peer list.

参数
  • from_head -- fetch from head of list or not

  • peer -- peer information

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

  • ESP_ERR_ESPNOW_ARG : invalid argument

  • ESP_ERR_ESPNOW_NOT_FOUND : peer is not found

bool esp_now_is_peer_exist(const uint8_t *peer_addr)

Peer exists or not.

参数

peer_addr -- peer MAC address

返回

  • true : peer exists

  • false : peer not exists

esp_err_t esp_now_get_peer_num(esp_now_peer_num_t *num)

Get the number of peers.

参数

num -- number of peers

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

  • ESP_ERR_ESPNOW_ARG : invalid argument

esp_err_t esp_now_set_pmk(const uint8_t *pmk)

Set the primary master key.

Attention

1. primary master key is used to encrypt local master key

参数

pmk -- primary master key

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

  • ESP_ERR_ESPNOW_ARG : invalid argument

esp_err_t esp_now_set_wake_window(uint16_t window)

Set wake window for esp_now to wake up in interval unit.

Attention

1. This configuration could work at connected status. When ESP_WIFI_STA_DISCONNECTED_PM_ENABLE is enabled, this configuration could work at disconnected status.

Attention

2. Default value is the maximum.

参数

window -- Milliseconds would the chip keep waked each interval, from 0 to 65535.

返回

  • ESP_OK : succeed

  • ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized

Structures

struct esp_now_peer_info

ESPNOW peer information parameters.

Public Members

uint8_t peer_addr[ESP_NOW_ETH_ALEN]

ESPNOW peer MAC address that is also the MAC address of station or softap

uint8_t lmk[ESP_NOW_KEY_LEN]

ESPNOW peer local master key that is used to encrypt data

uint8_t channel

Wi-Fi channel that peer uses to send/receive ESPNOW data. If the value is 0, use the current channel which station or softap is on. Otherwise, it must be set as the channel that station or softap is on.

wifi_interface_t ifidx

Wi-Fi interface that peer uses to send/receive ESPNOW data

bool encrypt

ESPNOW data that this peer sends/receives is encrypted or not

void *priv

ESPNOW peer private data

struct esp_now_peer_num

Number of ESPNOW peers which exist currently.

Public Members

int total_num

Total number of ESPNOW peers, maximum value is ESP_NOW_MAX_TOTAL_PEER_NUM

int encrypt_num

Number of encrypted ESPNOW peers, maximum value is ESP_NOW_MAX_ENCRYPT_PEER_NUM

struct esp_now_recv_info

ESPNOW packet information.

Public Members

uint8_t *src_addr

Source address of ESPNOW packet

uint8_t *des_addr

Destination address of ESPNOW packet

wifi_pkt_rx_ctrl_t *rx_ctrl

Rx control info of ESPNOW packet

struct esp_now_rate_config

ESPNOW rate config.

Public Members

wifi_phy_mode_t phymode

ESPNOW phymode of specified interface

wifi_phy_rate_t rate

ESPNOW rate of specified interface

bool ersu

ESPNOW using ersu send frame

bool dcm

ESPNOW using dcm rate to send frame

Macros

ESP_ERR_ESPNOW_BASE

ESPNOW error number base.

ESP_ERR_ESPNOW_NOT_INIT

ESPNOW is not initialized.

ESP_ERR_ESPNOW_ARG

Invalid argument

ESP_ERR_ESPNOW_NO_MEM

Out of memory

ESP_ERR_ESPNOW_FULL

ESPNOW peer list is full

ESP_ERR_ESPNOW_NOT_FOUND

ESPNOW peer is not found

ESP_ERR_ESPNOW_INTERNAL

Internal error

ESP_ERR_ESPNOW_EXIST

ESPNOW peer has existed

ESP_ERR_ESPNOW_IF

Interface error

ESP_ERR_ESPNOW_CHAN

Channel error

ESP_NOW_ETH_ALEN

Length of ESPNOW peer MAC address

ESP_NOW_KEY_LEN

Length of ESPNOW peer local master key

ESP_NOW_MAX_TOTAL_PEER_NUM

Maximum number of ESPNOW total peers

ESP_NOW_MAX_ENCRYPT_PEER_NUM

Maximum number of ESPNOW encrypted peers

ESP_NOW_MAX_DATA_LEN

Maximum length of ESPNOW data which is sent very time

Type Definitions

typedef struct esp_now_peer_info esp_now_peer_info_t

ESPNOW peer information parameters.

typedef struct esp_now_peer_num esp_now_peer_num_t

Number of ESPNOW peers which exist currently.

typedef struct esp_now_recv_info esp_now_recv_info_t

ESPNOW packet information.

typedef struct esp_now_rate_config esp_now_rate_config_t

ESPNOW rate config.

typedef void (*esp_now_recv_cb_t)(const esp_now_recv_info_t *esp_now_info, const uint8_t *data, int data_len)

Callback function of receiving ESPNOW data.

Attention

esp_now_info is a local variable,it can only be used in the callback.

Param esp_now_info

received ESPNOW packet information

Param data

received data

Param data_len

length of received data

typedef void (*esp_now_send_cb_t)(const uint8_t *mac_addr, esp_now_send_status_t status)

Callback function of sending ESPNOW data.

Param mac_addr

peer MAC address

Param status

status of sending ESPNOW data (succeed or fail)

Enumerations

enum esp_now_send_status_t

Status of sending ESPNOW data .

Values:

enumerator ESP_NOW_SEND_SUCCESS

Send ESPNOW data successfully

enumerator ESP_NOW_SEND_FAIL

Send ESPNOW data fail