la doc est dispo:
https://docs.espressif.com/projects/...uint8_t6size_t
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
Parameters
peer_addr -- peer MAC address
data -- data to send
len -- length of data
Returns
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
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