ESP send raw frames

// ESP send raw frames
// src https://stackoverflow.com/questions/46224416/esp8266-send-beacon-frame-with-deep-sleep-mode-does-not-work-properly

#include <ESP8266WiFi.h>
extern "C" {
  #include "user_interface.h"
}

void setup() {
  delay(500);
//  sendBeacon("ESP8266");
//  ESP.deepSleep(10e5);
}

void loop() {
  sendBeacon("ESP8266");
}

void sendBeacon(char* ssid) {
    // Randomize channel //
    byte channel = 1;
    wifi_set_channel(channel);

    uint8_t packet[128] = { 0x80, 0x00, //Frame Control
                        0x00, 0x00, //Duration
                /*4*/   0xff, 0xff, 0xff, 0xff, 0xff, 0xff, //Destination address
                /*10*/  0x01, 0x02, 0x03, 0x04, 0x05, 0x06, //Source address - overwritten later
                /*16*/  0x01, 0x02, 0x03, 0x04, 0x05, 0x06, //BSSID - overwritten to the same as the source address
                /*22*/  0xc0, 0x6c, //Seq-ctl
                //Frame body starts here
                /*24*/  0x83, 0x51, 0xf7, 0x8f, 0x0f, 0x00, 0x00, 0x00, //timestamp - the number of microseconds the AP has been active
                /*32*/  0xFF, 0x00, //Beacon interval
                /*34*/  0x01, 0x04, //Capability info
                /* SSID */
                /*36*/  0x00
                };

    int ssidLen = strlen(ssid);
    packet[37] = ssidLen;

    for(int i = 0; i < ssidLen; i++) {
      packet[38+i] = ssid[i];
    }

    uint8_t postSSID[13] = {0x01, 0x08, 0x82, 0x84, 0x8b, 0x96, 0x24, 0x30, 0x48, 0x6c, //supported rate
                        0x03, 0x01, 0x04 /*DSSS (Current Channel)*/ };

    for(int i = 0; i < 12; i++) {
      packet[38 + ssidLen + i] = postSSID[i];
    }

    packet[50 + ssidLen] = channel;

    // get SRC MAC
    unsigned char mac[6];
    WiFi.macAddress(mac);
    packet[10] = packet[16] = mac[0];
    packet[11] = packet[17] = mac[1];
    packet[12] = packet[18] = mac[2];
    packet[13] = packet[19] = mac[3];
    packet[14] = packet[20] = mac[4];
    packet[15] = packet[21] = mac[5];

    int packetSize = 51 + ssidLen;

    wifi_send_pkt_freedom(packet, packetSize, 0);
    delay(1);
}