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#62795 SerialPort ESP 8266 ESP8266 Wifi

Posted by JohanV on 22 May 2015 - 02:57 PM in Netduino 2 (and Netduino 1)

After some testing i reccomend for serial data processing, 

some short code that quickly handles the datarecieved interrupt.


and about a 100 or 150 msec handling the data, but this is al depending on your project off-course.


       private int recBufferLength = 0;
       private byte[] recBuffer = new byte[2048];
            /* Data reception interrupt handler */
       internal void DataReceived_Interrupt(object com, SerialDataReceivedEventArgs arg)
             // byte[] buffer = new byte[serialPort.BytesToRead];
             Int32 curRead = serialPort.Read(recBuffer, recBufferLength , serialPort.BytesToRead);
             recBufferLength += curRead;


// i use some sort of data process moment, each 100 or 150 msec.

// at this moment i turn the data into a string.


 sRecieveData += new String(System.Text.Encoding.UTF8.GetChars(recBuffer, 0, recBufferLength));
 recBuffer = new byte[2048];
Also if there is an incomplete http response from the ESP8266, remember how the request was made.
Http1.0 or HTTP1.1.
testing against a linux apache server the HTTP1.1 could use Chunked responses.
( there will be some strange identifier ?? 8d4 in this case.) http://en.wikipedia....ansfer_encoding
HTTP/1.1 200 OK
Date: Fri, 22 May 2015 14:54:29 GMT
Server: Apache/2.2.29 (Unix)
X-Powered-By: PHP/5.4.40
Connection: close
Transfer-Encoding: chunked
Content-Type: text/html; charset=ISO-8859-1
for a different request i get a response of 39342 bytes.
But still my response with the ESP8266 is choped at around 1450 bytes.
Connection: close
Accept: text/html
User-Agent: ESP8266
+IPD,1412:HTTP/1.1 200 OK
Content-Length: 39342
Content-Type: text/html
Last-Modified: Sun, 10 May 2015 19:52:13 GMT
Accept-Ranges: bytes
ETag: "2d348ccf5a8bd01:0"
Server: Microsoft-IIS/8.0
X-Powered-By: ASP.NET
Set-Cookie: ARRAffinity=0fc3cc817ad58a64bbaff8bc51eb48d3224777aeb37b322d17e1369cad947f99;Path=/;
Date: Fri, 22 May 2015 14:51:24 GMT
Connection: close
?<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "">
<meta content="en-us" http-equiv="Content-Language" />
<meta content="text/html; charset=utf-8" http-e

#62788 SerialPort ESP 8266 ESP8266 Wifi

Posted by JohanV on 22 May 2015 - 07:26 AM in Netduino 2 (and Netduino 1)

Also after getting some serial port data back, and do some string searching.

I did not check how long this takes. an array search will probably be a lot faster ?


                this.SendTimeOut = System.DateTime.Now;

                // search string
                for (int i1 = 0; i1 < 10000; ++i1)
                    test.IndexOf(":" + i1.ToString());
                Debug.Print(this.SendTimeOut +"::"+ System.DateTime.Now);

#62787 SerialPort ESP 8266 ESP8266 Wifi

Posted by JohanV on 22 May 2015 - 07:13 AM in Netduino 2 (and Netduino 1)

Hi Chris,


Thanks for the support, 

I did some string tests.


                this.SendTimeOut = System.DateTime.Now;
                System.String test = "";
                for (int i1 = 0; i1 < 10000; ++i1)
                    test += ":" + i1.ToString();
                Debug.Print(this.SendTimeOut +"::"+ System.DateTime.Now);
this itteration takes about 68 seconds for 10000 repeats.
And turns out it does only 147 times per second the ( += string function ).
so this is only 1200 bytes per second, not fast enough for the 9600 baud rate.
I will look into some array functions to do similar functionality.
I know the STM32F427 is quite fast with array functions.
Any one have some nice example that will run fast ?

#62773 SerialPort ESP 8266 ESP8266 Wifi

Posted by JohanV on 21 May 2015 - 08:41 AM in Netduino 2 (and Netduino 1)

Hi Chris,


Actualy, i changed the speed to 115200, and get about 1450 bytes at each http response.

so quite an improvement. Different than i expected....

But some data is still choped, at the end, this is not a real problem, for only sending some simple sensor data to a webserver or database.


I get the "RXOver" type in ErrorReceived_Interrupt(object sender, SerialErrorReceivedEventArgs e)

This is an input buffer overflow ?


So to fix this i need to speed up reading and processing data from the input buffer ?


I'm still wondering what the slow part is of this code (DataReceived_Interrupt) ?

there is an example of the esp8266 driver ( )

this code handles the return data of the module in arrays, i think to avoid slow string processing ?

#62750 SerialPort ESP 8266 ESP8266 Wifi

Posted by JohanV on 19 May 2015 - 11:26 PM in Netduino 2 (and Netduino 1)

This module has only 256 bytes cache. as far as i can test, and read on the internet.


also i did not think about that the data rate could be to slow, 

during testing i saw with the interrupt routine many times only get 2 to 4 characters.

but i will change it and see what happens.


i know the baud rate can be changed of this module. it started with 115200, and i thought it would be to fast for netmf.


so it's not the string manipulation that is slow but rather the interupt trigger fired many times ?


if i get serial data back bigger than about 256 bytes the stream is choped at irregular places





i will try it tomorrow.

#62728 SerialPort ESP 8266 ESP8266 Wifi

Posted by JohanV on 18 May 2015 - 12:47 PM in Netduino 2 (and Netduino 1)

Hello I'm trying to interface the ESP8266 WiFi with AT commands.



Also any one intresting in WiFi for the Netduino,

( better just buy the new Netduino 3 with out of the box Wifi !!! :D )



At the moment i'm using the module, with this firmware (0018000902-AI03).

At 9600 bit ps.



most functions are working now.


my problem is the ESP 8266 only have 256 byte buffer. so to read the 256 byte buffer ( 2048 bit. ).

after about 200 ms you start to loose data.


At the moment i spend quite some time to get me familiar to the .net micro framework serial port.


The serial port is read with an interupt.

This interupt is started in a new thread. so this is triggered after some data is recieved.

somtimes 2 bytes somtimes 10 or more.


serialPort.DataReceived += new SerialDataReceivedEventHandler(DataReceived_Interrupt);

serialPort.ErrorReceived += new SerialErrorReceivedEventHandler(ErrorReceived_Interrupt);


Also at first i did not have an Error Revieved interrupt, and was unable to find the problems i had with this module.

turns out it's an buffer input overflow. ( 256 bytes max ).


I changed the handling of the recieved data, and turns out, my approach is to slowy ( or the neduino ? ). For this module.

I'm using some string functions that i suspect are to slowly ?


static System.String sRecieveData = "";

static SerialPort serialPort;


//* Data reception interrupt handler */

internal void DataReceived_Interrupt(object com, SerialDataReceivedEventArgs arg)


  byte[] bytes = new byte[serialPort.BytesToRead];

  // read the bytes

  serialPort.Read(bytes, 0, bytes.Length);

  // convert the bytes into a string

  String strLine = new String(System.Text.Encoding.UTF8.GetChars(bytes, 0, bytes.Length));

  sRecieveData += strLine;




/* Data reception interrupt handler */

internal void DataReceived_Interrupt(object com, SerialDataReceivedEventArgs arg)


  byte[] buf = new byte[1];

  System.String sRecievePart = "";

  while (serialPort.BytesToRead > 0)


    serialPort.Read(buf, 0, 1);

    sRecievePart += (char)buf[0];


  sRecieveData += sRecievePart;



So my question is what is the best way to handle the recieved serial data ? so i not get the buffer overflow error. 




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