Send data periodically as a server to my client in arduino ESP8226 - tcp

Question

I'm using NodeMCU board to communicate a laptop through WiFi. Basic communication is ok with a code like this:
void loop (){
WiFiClient client = server.available();
if (client) {
while (client.connected()){
client.println(Data_mem[0]);
delay(2000);
}
client.stop(); // tarminates the connection with the client
}
}
But when I want to send data a Timer Tick, it seems the client couldn't connect to me.
void setup(){
....
//Initialize Ticker every 40ms
Data_Rec.attach_ms(40, 40ms_Data );
}
void 40ms_Data (){
WiFiClient client = server.available();
Serial.println("40ms_Data A");
if (client) {
Serial.println("40ms_Data B");
if (client .connected()){
Serial.println("40ms_Data C");
client.println(40ms_Data [0]);
}
else{
client.stop();
}
}
}
I arduino serial monitor, i see only this:
40ms_Data A \r\n
40ms_Data A \r\n
....
So, could anyone help me? maybe it a problem of WiFiClient deceleration in a non-forever loop (like example 1). But I have no idea to fix it.
According to M.R.'s idea, this is my complete new code:
#include <ESP8266WiFi.h>
#include <Ticker.h>
/* Put your SSID & Password */
const char* ssid = "NodeMCU"; // Enter SSID here
const char* password = "12345678"; //Enter Password here
/* Put IP Address details */
IPAddress local_ip(192,168,1,1);
IPAddress gateway(192,168,1,1);
IPAddress subnet(255,255,255,0);
WiFiServer server(80);
const int CLIENT_TIMEOUT = 2000;
Ticker Data_Rec;
bool Sending_40ms_Start_Flag = false;
void setup() {
Serial.begin(115200);
pinMode(D0, OUTPUT);
WiFi.softAP(ssid, password);
WiFi.softAPConfig(local_ip, gateway, subnet);
delay(100);
server.begin();
Serial.println("HTTP server started");
Data_Rec.attach_ms(500, flag_enable);//500ms is for test
}
void flag_enable(){
//Read FPGA Data from SPI
//...
Sending_40ms_Start_Flag = true;
}
void loop(){
WiFiClient client = server.available();
if (client) {
while(client.connected()){
Serial.println("40ms_Data B");
if (Sending_40ms_Start_Flag){
client.println("Server listening.\r");
Sending_40ms_Start_Flag = false;
}
delay(1);//without this delay, ESP would be reset(because it cannot handle background processes)
}
// else{
// client.stop();
// }
}
}
This code worked. But the server RST the TCP connection after sending one,two or tree "Server listening." as Wireshark shows: Wireshark Capture
What is probable cause of TCP Reset from ESP?

Answer 1

Besides that some syntax errors in your code:
A good solution is to create a static pointer object from client and pass it as an argument to ms40_Data function:
void ms40_Data(WiFiClient *client)
{
Serial.println("40ms_Data A");
if (*client)
{
Serial.println("40ms_Data B");
if (client->connected())
{
Serial.println("40ms_Data C");
//client.println(40ms_Data [0]);
}
else
{
client->stop();
}
}
}
void setup()
{
...
// create a static object from WiFiClient
static WiFiClient client = server.available();
//Initialize Ticker every 40ms
Data_Rec.attach_ms(40, ms40_Data, &client);
}
void loop()
{
}
Another solution is, you can set a flag inside your ticker and then call your ms40_Data function:
bool start_40ms_Data = false;
void ms40_Data()
{
static WiFiClient client = server.available();
Serial.println("40ms_Data A");
if (client)
{
Serial.println("40ms_Data B");
if (client.connected())
{
Serial.println("40ms_Data C");
//client.println(40ms_Data [0]);
}
else
{
client.stop();
}
}
}
void flag_enable()
{
start_40ms_Data = true;
}
void setup()
{
...
//Initialize Ticker every 40ms
Data_Rec.attach_ms(40, flag_enable);
}
void loop()
{
if (start_40ms_Data)
{
ms40_Data();
start_40ms_Data = false;
}
}

Answer 2

The point is to adding this to setup function:
WiFi.mode(WIFI_AP);
Full explanation: Here
Thank you,