Chapter 2. API Reference
esp_err_t esp_now_unregister_recv_cb(void)
Unregister callback function of receiving ESPNOW data.
Return
• 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.
Return
• ESP_OK : succeed
• ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized
• ESP_ERR_ESPNOW_INTERNAL : internal error
Parameters
• cb: callback function of sending ESPNOW data
esp_err_t esp_now_unregister_send_cb(void)
Unregister callback function of sending ESPNOW data.
Return
• 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
Return
• 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
• ESP_ERR_ESPNOW_NOT_FOUND : peer is not found
• ESP_ERR_ESPNOW_IF : current WiFi interface doesn’t match that of peer
Parameters
• peer_addr: peer MAC address
• data: data to send
• len: length of data
esp_err_t esp_now_add_peer(const esp_now_peer_info_t *peer)
Add a peer to peer list.
Return
• 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
Parameters
• peer: peer information
esp_err_t esp_now_del_peer(const uint8_t *peer_addr)
Delete a peer from peer list.
Return
• ESP_OK : succeed
• ESP_ERR_ESPNOW_NOT_INIT : ESPNOW is not initialized
• ESP_ERR_ESPNOW_ARG : invalid argument
Espressif Systems 131
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