Tutorial: Web Server with the ESP8266 WiFi Module

Erich Styger

Dec. 02, 14 · Interview

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It has been a while since my first post about the ESP8266 (see “Cheap and Simple WiFi with ESP8266 for the FRDM Board“). The ESP8266 is a new inexpensive ($4.50) WiFi module which makes it easy to connect to the network or internet. Finally this week-end I have found the time to write up a tutorial: how to implement a WiFi web server for the ESP8266 WiFi module and the Freescale FRDM-KL25Z board:

WSP8266 Web Server

FRDM-KL25Z with ESP8266 WiFi Module

Outline

In this tutorial I’m using a Freescale FRDM-KL25Z board as a web server, using theESP8266 board. The ESP8266 is a ‘less than $4.5′ WiFi board getting more and more popular as an IoT board. There is even a way to run the ESP8266 standalone (because it has a full processor on that board). However, that development is still in the flux and rather unstable. Instead, I’m using a serial connection to the ESP8266 instead. With this, any small microcontroller can send and receive data from the internet: connect that board to a microcontroller with 3.3V, GND, Tx and Rx, and you have a W-LAN connection!

I’m using in this tutorial Eclipse with GNU/GDB with Processor Expert, but with the steps in this tutorial you should be able to use any other toolchain too.

As things might change in the future with different firmware on the ESP8266: the firmware I’m having on the board is version 00160901.

Board Connections

Since my first post on the ESP8266 I have cleaned up the wiring. The pins are as below for the ESP8266:

ESP8266 Pins

Because the ESP8266 can take > 200 mA, I’m using a 5-to-3.3V DC-DC converter. I measured around 70 to 90 mA, so it is not (yet) really needed, but I wanted to use it to protect to board. The ESP8266 Rx and Tx are connected to the microcontroller Tx and Rx pins. A general frustration point for the ESP8266 module is the connection oft the remaining pins. What worked for me is to connect CH_PD to 3.3V and leaving RST,GPIO0 and GPIO2 unconnected/floating.

Wiring Setup with FRDM-KL25Z and ESP8266

Communication Protocol

I recommend to use a logic analyzer to verify the communication between the ESP8266 and the microcontroller. My module communicates with 115200, but I see reports that other modules (other firmware) can use a different baud.

The module uses an AT command send. The simplest command is to send “AT\r\n” and it responds with “AT\r\r\n\r\nOK\r\n”:

AT Command Sent to ESP8266

In this tutorial I’m using a command line shell (see “A Shell for the Freedom KL25Z Board“) to have a manual mode to send commands to the module. More about this later.

Project Creation

You can use my project and source files available on GitHub (see link at the end of this article). Or create your own project. My project is using the Kinetis Design Studio and for the FRDM-KL25Z board (MKL25Z128VLK4).

I have created a project for Processor Expert, as I’m using several components of it:

Processor Expert Project

For the project I have several files added:

ESP8266 Project in Eclipse

With the following source files:

Application.c/.h: This runs the application and web server program
ESP8266.c/.h: Driver for the ESP8266
Events.c/.h: Processor Expert event hooks
main.c: main entry point
Shell.c/.h: command line interface

Sources

Project and Source files are available on GitHub here:
https://github.com/ErichStyger/mcuoneclipse/tree/master/Examples/KDS/FRDM-KL25Z/FRDM-KL25Z_ESP8266

Please check the latest source files on GitHub. At the time of writing this article, I’m using the following:

Shell.h is the interface to command line shell:

/*
 * Shell.h
 *
 *      Author: Erich Styger
 */
  
#ifndef SHELL_H_
#define SHELL_H_
  
/*!
 * \brief Shell parse routine
 */
voidSHELL_Parse(void);
  
/*!
 * \brief Shell initialization
 */
voidSHELL_Init(void);
  
#endif /* SHELL_H_ */

Shell.c implements the application part of the shell:

/*
 * Shell.c
 *
 *      Author: Erich Styger
 */
  
#include "Shell.h"
#include "CLS1.h"
#include "ESP8266.h"
  
/* table with shell parser/handler */
staticconstCLS1_ParseCommandCallback CmdParserTable[] =
{
  CLS1_ParseCommand,
  ESP_ParseCommand,
  NULL /* sentinel */
};
  
staticunsigned charlocalConsole_buf[48]; /* buffer for command line */
  
voidSHELL_Parse(void) {
  (void)CLS1_ReadAndParseWithCommandTable(localConsole_buf, sizeof(localConsole_buf), CLS1_GetStdio(), CmdParserTable);
}
  
voidSHELL_Init(void) {
  localConsole_buf[0] = '\0'; /* initialize buffer */
}

ESP8266.h is the interface to the WiFi module:

/*
 * ESP8266.h
 *
 *      Author: Erich Styger
 */
  
#ifndef ESP8266_H_
#define ESP8266_H_
  
#include "CLS1.h"
  
#define ESP_DEFAULT_TIMEOUT_MS    (100)
  /*!< Default timeout value in milliseconds */
  
/*!
 * \brief Command line parser routine
 * \param cmd Pointer to command line string
 * \param handled Return value if command has been handled
 * \param io Standard Shell I/O handler
 * \return Error code, ERR_OK for no failure
 */
uint8_t ESP_ParseCommand(constunsigned char*cmd, bool *handled, constCLS1_StdIOType *io);
  
/*!
 * \brief Send a string to th ESP8266 module
 * \param str String to send, "\r\n" will be appended
 * \param io Shell I/O handler or NULL if not used
 * \return Error code, ERR_OK for no failure
 */
uint8_t ESP_SendStr(constuint8_t *str, CLS1_ConstStdIOType *io);
  
/*!
 * \brief Used to send an AT command to the ESP8266 module
 * \param cmd Command string to send
 * \param rxBuf Buffer for the response, can be NULL
 * \param rxBufSize Size of response buffer
 * \param expectedTailStr Expected response from the module, can be NULL
 * \param msTimeout Timeout time in milliseconds
 * \param io Shell I/O handler or NULL if not used
 * \return Error code, ERR_OK for no failure
 */
uint8_t ESP_SendATCommand(uint8_t *cmd, uint8_t *rxBuf, size_t rxBufSize, uint8_t *expectedTailStr, uint16_t msTimeout, constCLS1_StdIOType *io);
  
/*!
 * \brief Read from the serial line from the module until a sentinel char is received
 * \param buf
 * \param bufSize
 * \param sentinelChar
 * \param timeoutMs Timeout time in milliseconds
 * \return Error code, ERR_OK for no failure
 */
uint8_t ESP_ReadCharsUntil(uint8_t *buf, size_t bufSize, uint8_t sentinelChar, uint16_t timeoutMs);
  
/*!
 * \brief Sends an AT command to test the connection
 * \return Error code, ERR_OK for no failure
 */
uint8_t ESP_TestAT(void);
  
/*!
 * \brief Restarts the ESP8266 module
 * \param io Shell I/O handler or NULL if not used
 * \param timeoutMs Timeout time in milliseconds
 * \return Error code, ERR_OK for no failure
 */
uint8_t ESP_Restart(constCLS1_StdIOType *io, uint16_t timeoutMs);
  
/*!
 * \brief Set the current mode of the module
 * \param mode Where <mode> is 1=Sta, 2=AP or 3=both
 * \return Error code, ERR_OK for no failure
 */
uint8_t ESP_SelectMode(uint8_t mode);
  
/*!
 * \Brief returns the firmware version string
 * \param fwBuf Buffer for the string
 * \param fwBufSize Size of buffer in bytes
 * \return Error code, ERR_OK for no failure
 */
uint8_t ESP_GetFirmwareVersionString(uint8_t *fwBuf, size_t fwBufSize);
  
/*!
 * \brief Join an access point.
 * \param ssid SSID of access point
 * \param pwd Password of access point
 * \param nofRetries Number of connection retries
 * \param io Shell I/O or NULL if not used
 * \return Error code, ERR_OK for no failure
 */
uint8_t ESP_JoinAP(constuint8_t *ssid, constuint8_t *pwd, intnofRetries, CLS1_ConstStdIOType *io);
  
/*!
 * \brief Scans for an IPD message sent by the module
 * \param msgBuf Pointer to the message buffer where to store the message
 * \param msgBufSize Size of message buffer
 * \param ch_id Pointer to where to store the channel/id
 * \param size Pointer where to store the size of the message
 * \param isGet TRUE if it is a GET message, FALSE for a POST message
 * \param timeoutMs Error code, ERR_OK for no failure
 * \param io
 * \return Error code, ERR_OK for no failure
 */
uint8_t ESP_GetIPD(uint8_t *msgBuf, size_t msgBufSize, uint8_t *ch_id, uint16_t *size, bool *isGet, uint16_t timeoutMs, constCLS1_StdIOType *io);
  
/*!
 * \brief Closes a connection
 * \param channel Channel ID
 * \param io Error code, ERR_OK for no failure
 * \param timeoutMs Error code, ERR_OK for no failure
 * \return Error code, ERR_OK for no failure
 */
uint8_t ESP_CloseConnection(uint8_t channel, constCLS1_StdIOType *io, uint16_t timeoutMs);
  
/*!
 * \brief Used to determine if the web server is running or not.
 * \return TRUE if web server has beens started
 */
bool ESP_IsServerOn(void);
  
/*!
 * \brief Driver initialization
 */
voidESP_Init(void);
  
/*!
 * \brief Driver de-initialization
 */
voidESP_Deinit(void);
  
#endif /* ESP8266_H_ */

And the ESP8266 driver is in ESP8266.c which implements all the low level SPI access functions, the functional implementation and a command line shell interface:

/*
 * ESP8266.c
 *
 *      Author: Erich Styger
 */
  
#include "ESP8266.h"
#include "Shell.h"
#include "UTIL1.h"
#include "CLS1.h"
#include "AS2.h"
#include "WAIT1.h"
  
staticbool ESP_WebServerIsOn = FALSE;
  
bool ESP_IsServerOn(void) {
  returnESP_WebServerIsOn;
}
  
staticvoidSend(unsigned char*str) {
  while(*str!='\0') {
    AS2_SendChar(*str);
    str++;
  }
}
  
staticvoidSkipNewLines(constunsigned char**p) {
  while(**p=='\n'|| **p=='\r') {
    (*p)++; /* skip new lines */
  }
}
  
uint8_t ESP_ReadCharsUntil(uint8_t *buf, size_t bufSize, uint8_t sentinelChar, uint16_t timeoutMs) {
  uint8_t ch;
  uint8_t res = ERR_OK;
  
  if(bufSize<=1) {
    returnERR_OVERRUN; /* buffer to small */
  }
  buf[0] = '\0'; buf[bufSize-1] = '\0'; /* always terminate */
  bufSize--;
  for(;;) { /* breaks */
    if(bufSize==0) {
      res = ERR_OVERRUN;
      break;
    }
    if(AS2_GetCharsInRxBuf()>0) {
      (void)AS2_RecvChar(&ch);
      *buf = ch;
      buf++;
      bufSize--;
      if(ch==sentinelChar) {
        *buf = '\0'; /* terminate string */
        break; /* sentinel found */
      }
    } else{
      if(timeoutMs>10) {
        WAIT1_WaitOSms(5);
        timeoutMs -= 5;
      } else{
        res = ERR_NOTAVAIL; /* timeout */
        break;
      }
    }
  }
  returnres;
}
  
staticuint8_t RxResponse(unsigned char*rxBuf, size_t rxBufLength, unsigned char*expectedTail, uint16_t msTimeout) {
  unsigned charch;
  uint8_t res = ERR_OK;
  unsigned char*p;
  
  if(rxBufLength < sizeof("x\r\n")) {
    returnERR_OVERFLOW; /* not enough space in buffer */
  }
  p = rxBuf;
  p[0] = '\0';
  for(;;) { /* breaks */
    if(msTimeout == 0) {
      break; /* will decide outside of loop if it is a timeout. */
    } elseif(rxBufLength == 0) {
      res = ERR_OVERFLOW; /* not enough space in buffer */
      break;
    } elseif(AS2_GetCharsInRxBuf() > 0) {
#if0
      if(AS2_RecvChar(&ch) != ERR_OK) {
        res = ERR_RXEMPTY;
        break;
      }
#else
      /* might get an overrun OVERRUN_ERR error here? Ignoring error for now */
      (void)AS2_RecvChar(&ch);
#endif
      *p++ = ch;
      *p = '\0'; /* always terminate */
      rxBufLength--;
    } elseif(expectedTail!=NULL && expectedTail[0]!='\0'
          && UTIL1_strtailcmp(rxBuf, expectedTail) == 0) {
      break; /* finished */
    } else{
      WAIT1_WaitOSms(1);
      msTimeout--;
    }
  } /* for */
  if(msTimeout==0) { /* timeout! */
    if(expectedTail[0] != '\0'/* timeout, and we expected something: an error for sure */
        || rxBuf[0] == '\0'/* timeout, did not know what to expect, but received nothing? There has to be a response. */
       )
    {
      res = ERR_FAULT;
    }
  }
  returnres;
}
  
uint8_t ESP_SendATCommand(uint8_t *cmd, uint8_t *rxBuf, size_t rxBufSize, uint8_t *expectedTailStr, uint16_t msTimeout, constCLS1_StdIOType *io) {
  uint16_t snt;
  uint8_t res;
  
  if(rxBuf!=NULL) {
    rxBuf[0] = '\0';
  }
  if(io!=NULL) {
    CLS1_SendStr("sending>>:\r\n", io->stdOut);
    CLS1_SendStr(cmd, io->stdOut);
  }
  if(AS2_SendBlock(cmd, (uint16_t)UTIL1_strlen((char*)cmd), &snt) != ERR_OK) {
    returnERR_FAILED;
  }
  if(rxBuf!=NULL) {
    res = RxResponse(rxBuf, rxBufSize, expectedTailStr, msTimeout);
    if(io!=NULL) {
      CLS1_SendStr("received<<:\r\n", io->stdOut);
      CLS1_SendStr(rxBuf, io->stdOut);
    }
  }
  returnres;
}
  
uint8_t ESP_TestAT(void) {
  /* AT */
  uint8_t rxBuf[sizeof("AT\r\r\n\r\nOK\r\n")];
  uint8_t res;
  
  res = ESP_SendATCommand("AT\r\n", rxBuf, sizeof(rxBuf), "AT\r\r\n\r\nOK\r\n", ESP_DEFAULT_TIMEOUT_MS, NULL);
  returnres;
}
  
uint8_t ESP_Restart(constCLS1_StdIOType *io, uint16_t timeoutMs) {
  /* AT+RST */
  uint8_t rxBuf[sizeof("AT+RST\r\r\n\r\nOK\r\n")];
  uint8_t res;
  uint8_t buf[64];
  
  AS2_ClearRxBuf(); /* clear buffer */
  res = ESP_SendATCommand("AT+RST\r\n", rxBuf, sizeof(rxBuf), "AT+RST\r\r\n\r\nOK\r\n", ESP_DEFAULT_TIMEOUT_MS, io);
  if(res==ERR_OK) {
    for(;;) {
      ESP_ReadCharsUntil(buf, sizeof(buf), '\n', 1000);
      if(io!=NULL) {
        CLS1_SendStr(buf, io->stdOut);
      }
      if(UTIL1_strncmp(buf, "ready", sizeof("ready")-1)==0) { /* wait until ready message from module */
        break; /* module has restarted */
      }
    }
  }
  AS2_ClearRxBuf(); /* clear buffer */
  returnres;
}
  
uint8_t ESP_CloseConnection(uint8_t channel, constCLS1_StdIOType *io, uint16_t timeoutMs) {
  /* AT+CIPCLOSE=<channel> */
  uint8_t res;
  uint8_t cmd[64];
  
  UTIL1_strcpy(cmd, sizeof(cmd), "AT+CIPCLOSE=");
  UTIL1_strcatNum8u(cmd, sizeof(cmd), channel);
  UTIL1_strcat(cmd, sizeof(cmd), "\r\n");
  res = ESP_SendATCommand(cmd, NULL, 0, "Unlink\r\n", timeoutMs, io);
  returnres;
}
  
uint8_t ESP_SetNumberOfConnections(uint8_t nof, constCLS1_StdIOType *io, uint16_t timeoutMs) {
  /* AT+CIPMUX=<nof>, 0: single connection, 1: multiple connections */
  uint8_t res;
  uint8_t cmd[sizeof("AT+CIPMUX=12\r\n")];
  uint8_t rxBuf[sizeof("AT+CIPMUX=12\r\n\r\nOK\r\n")+10];
  
  if(nof>1) { /* only 0 and 1 allowed */
    if(io!=NULL) {
      CLS1_SendStr("Wrong number of connection parameter!\r\n", io->stdErr);
    }
    returnERR_FAILED;
  }
  UTIL1_strcpy(cmd, sizeof(cmd), "AT+CIPMUX=");
  UTIL1_strcatNum8u(cmd, sizeof(cmd), nof);
  UTIL1_strcat(cmd, sizeof(cmd), "\r\n");
  res = ESP_SendATCommand(cmd, rxBuf, sizeof(rxBuf), "OK\r\n", timeoutMs, io);
  returnres;
}
  
uint8_t ESP_SetServer(bool startIt, uint16_t port, constCLS1_StdIOType *io, uint16_t timeoutMs) {
  /* AT+CIPSERVER=<en>,<port>, where <en>: 0: stop, 1: start */
  uint8_t res;
  uint8_t cmd[sizeof("AT+CIPSERVER=1,80\r\n\r\nOK\r\n")+sizeof("no change")];
  uint8_t rxBuf[sizeof("AT+CIPSERVER=1,80\r\n\r\nOK\r\n")+sizeof("no change")];
  
  UTIL1_strcpy(cmd, sizeof(cmd), "AT+CIPSERVER=");
  if(startIt) {
    UTIL1_strcat(cmd, sizeof(cmd), "1,");
  } else{
    UTIL1_strcat(cmd, sizeof(cmd), "0,");
  }
  UTIL1_strcatNum16u(cmd, sizeof(cmd), port);
  UTIL1_strcat(cmd, sizeof(cmd), "\r\n");
  res = ESP_SendATCommand(cmd, rxBuf, sizeof(rxBuf), "OK\r\n", timeoutMs, io);
  if(res!=ERR_OK) { /* accept "no change" too */
    UTIL1_strcpy(cmd, sizeof(cmd), "AT+CIPSERVER=");
    if(startIt) {
      UTIL1_strcat(cmd, sizeof(cmd), "1,");
    } else{
      UTIL1_strcat(cmd, sizeof(cmd), "0,");
    }
    UTIL1_strcatNum16u(cmd, sizeof(cmd), port);
    UTIL1_strcat(cmd, sizeof(cmd), "\r\r\nno change\r\n");
    if(UTIL1_strcmp(rxBuf, cmd)==0) {
      res = ERR_OK;
    }
  }
  returnres;
}
  
uint8_t ESP_SelectMode(uint8_t mode) {
  /* AT+CWMODE=<mode>, where <mode> is 1=Sta, 2=AP or 3=both */
  uint8_t txBuf[sizeof("AT+CWMODE=x\r\n")];
  uint8_t rxBuf[sizeof("AT+CWMODE=x\r\r\nno change\r\n")];
  uint8_t expected[sizeof("AT+CWMODE=x\r\r\nno change\r\n")];
  uint8_t res;
  
  if(mode<1|| mode>3) {
    returnERR_RANGE; /* only 1, 2 or 3 */
  }
  UTIL1_strcpy(txBuf, sizeof(txBuf), "AT+CWMODE=");
  UTIL1_strcatNum16u(txBuf, sizeof(txBuf), mode);
  UTIL1_strcat(txBuf, sizeof(txBuf), "\r\n");
  UTIL1_strcpy(expected, sizeof(expected), "AT+CWMODE=");
  UTIL1_strcatNum16u(expected, sizeof(expected), mode);
  UTIL1_strcat(expected, sizeof(expected), "\r\r\n\n");
  res = ESP_SendATCommand(txBuf, rxBuf, sizeof(rxBuf), expected, ESP_DEFAULT_TIMEOUT_MS, NULL);
  if(res!=ERR_OK) {
    /* answer could be as well "AT+CWMODE=x\r\r\nno change\r\n"!! */
    UTIL1_strcpy(txBuf, sizeof(txBuf), "AT+CWMODE=");
    UTIL1_strcatNum16u(txBuf, sizeof(txBuf), mode);
    UTIL1_strcat(txBuf, sizeof(txBuf), "\r\n");
    UTIL1_strcpy(expected, sizeof(expected), "AT+CWMODE=");
    UTIL1_strcatNum16u(expected, sizeof(expected), mode);
    UTIL1_strcat(expected, sizeof(expected), "\r\r\nno change\r\n");
    if(UTIL1_strcmp(rxBuf, expected)==0) {
      res = ERR_OK;
    }
  }
  returnres;
}
  
uint8_t ESP_GetFirmwareVersionString(uint8_t *fwBuf, size_t fwBufSize) {
  /* AT+GMR */
  uint8_t rxBuf[32];
  uint8_t res;
  constunsigned char*p;
  
  res = ESP_SendATCommand("AT+GMR\r\n", rxBuf, sizeof(rxBuf), "\r\n\r\nOK\r\n", ESP_DEFAULT_TIMEOUT_MS, NULL);
  if(res!=ERR_OK) {
    if(UTIL1_strtailcmp(rxBuf, "\r\n\r\nOK\r\n")) {
      res = ERR_OK;
    }
  }
  if(res==ERR_OK) {
    if(UTIL1_strncmp(rxBuf, "AT+GMR\r\r\n", sizeof("AT+GMR\r\r\n")-1)==0) { /* check for beginning of response */
      UTIL1_strCutTail(rxBuf, "\r\n\r\nOK\r\n"); /* cut tailing response */
      p = rxBuf+sizeof("AT+GMR\r\r\n")-1;  /* skip beginning */
      UTIL1_strcpy(fwBuf, fwBufSize, p); /* copy firmware information string */
    } else{
      res = ERR_FAILED;
    }
  }
  if(res!=ERR_OK) {
    UTIL1_strcpy(fwBuf, fwBufSize, "ERROR"); /* default error */
  }
  returnres;
}
  
uint8_t ESP_GetIPAddrString(uint8_t *ipBuf, size_t ipBufSize) {
  /* AT+CIFSR */
  uint8_t rxBuf[32];
  uint8_t res;
  constunsigned char*p;
  
  res = ESP_SendATCommand("AT+CIFSR\r\n", rxBuf, sizeof(rxBuf), NULL, ESP_DEFAULT_TIMEOUT_MS, NULL);
  if(res!=ERR_OK) {
    if(UTIL1_strtailcmp(rxBuf, "\r\n")) {
      res = ERR_OK;
    }
  }
  if(res==ERR_OK) {
    if(UTIL1_strncmp(rxBuf, "AT+CIFSR\r\r\n", sizeof("AT+CIFSR\r\r\n")-1)==0) { /* check for beginning of response */
      UTIL1_strCutTail(rxBuf, "\r\n"); /* cut tailing response */
      p = rxBuf+sizeof("AT+CIFSR\r\r\n")-1; /* skip beginning */
      SkipNewLines(&p);
      UTIL1_strcpy(ipBuf, ipBufSize, p); /* copy IP information string */
    } else{
      res = ERR_FAILED;
    }
  }
  if(res!=ERR_OK) {
    UTIL1_strcpy(ipBuf, ipBufSize, "ERROR");
  }
  returnres;
}
  
uint8_t ESP_GetModeString(uint8_t *buf, size_t bufSize) {
  /* AT+CWMODE? */
  uint8_t rxBuf[32];
  uint8_t res;
  constunsigned char*p;
  
  res = ESP_SendATCommand("AT+CWMODE?\r\n", rxBuf, sizeof(rxBuf), "\r\n\r\nOK\r\n", ESP_DEFAULT_TIMEOUT_MS, NULL);
  if(res==ERR_OK) {
    if(UTIL1_strncmp(rxBuf, "AT+CWMODE?\r\r\n+CWMODE:", sizeof("AT+CWMODE?\r\r\n+CWMODE:")-1)==0) { /* check for beginning of response */
      UTIL1_strCutTail(rxBuf, "\r\n\r\nOK\r\n"); /* cut tailing response */
      p = rxBuf+sizeof("AT+CWMODE?\r\r\n+CWMODE:")-1; /* skip beginning */
      UTIL1_strcpy(buf, bufSize, p); /* copy information string */
    } else{
      res = ERR_FAILED;
    }
  }
  if(res!=ERR_OK) {
    UTIL1_strcpy(buf, bufSize, "ERROR");
  }
  returnres;
}
  
uint8_t ESP_GetCIPMUXString(uint8_t *cipmuxBuf, size_t cipmuxBufSize) {
  /* AT+CIPMUX? */
  uint8_t rxBuf[32];
  uint8_t res;
  constunsigned char*p;
  
  res = ESP_SendATCommand("AT+CIPMUX?\r\n", rxBuf, sizeof(rxBuf), "\r\n\r\nOK\r\n", ESP_DEFAULT_TIMEOUT_MS, NULL);
  if(res==ERR_OK) {
    if(UTIL1_strncmp(rxBuf, "AT+CIPMUX?\r\r\n+CIPMUX:", sizeof("AT+CIPMUX?\r\r\n+CIPMUX:")-1)==0) { /* check for beginning of response */
      UTIL1_strCutTail(rxBuf, "\r\n\r\nOK\r\n"); /* cut tailing response */
      p = rxBuf+sizeof("AT+CIPMUX?\r\r\n+CIPMUX:")-1; /* skip beginning */
      UTIL1_strcpy(cipmuxBuf, cipmuxBufSize, p); /* copy IP information string */
    } else{
      res = ERR_FAILED;
    }
  }
  if(res!=ERR_OK) {
    UTIL1_strcpy(cipmuxBuf, cipmuxBufSize, "ERROR");
  }
  returnres;
}
  
uint8_t ESP_GetConnectedAPString(uint8_t *apBuf, size_t apBufSize) {
  /* AT+CWJAP? */
  uint8_t rxBuf[48];
  uint8_t res;
  constunsigned char*p;
  
  res = ESP_SendATCommand("AT+CWJAP?\r\n", rxBuf, sizeof(rxBuf), "\r\n\r\nOK\r\n", ESP_DEFAULT_TIMEOUT_MS, NULL);
  if(res==ERR_OK) {
    if(UTIL1_strncmp(rxBuf, "AT+CWJAP?\r\r\n+CWJAP:\"", sizeof("AT+CWJAP?\r\r\n+CWJAP:\"")-1)==0) { /* check for beginning of response */
      UTIL1_strCutTail(rxBuf, "\"\r\n\r\nOK\r\n"); /* cut tailing response */
      p = rxBuf+sizeof("AT+CWJAP?\r\r\n+CWJAP:\"")-1; /* skip beginning */
      UTIL1_strcpy(apBuf, apBufSize, p); /* copy IP information string */
    } else{
      res = ERR_FAILED;
    }
  }
  if(res!=ERR_OK) {
    UTIL1_strcpy(apBuf, apBufSize, "ERROR");
  }
  returnres;
  
}
  
staticuint8_t JoinAccessPoint(constuint8_t *ssid, constuint8_t *pwd, CLS1_ConstStdIOType *io) {
  /* AT+CWJAP="<ssid>","<pwd>" */
  uint8_t txBuf[48];
  uint8_t rxBuf[64];
  uint8_t expected[48];
  
  UTIL1_strcpy(txBuf, sizeof(txBuf), "AT+CWJAP=\"");
  UTIL1_strcat(txBuf, sizeof(txBuf), ssid);
  UTIL1_strcat(txBuf, sizeof(txBuf), "\",\"");
  UTIL1_strcat(txBuf, sizeof(txBuf), pwd);
  UTIL1_strcat(txBuf, sizeof(txBuf), "\"\r\n");
  
  UTIL1_strcpy(expected, sizeof(expected), "AT+CWJAP=\"");
  UTIL1_strcat(expected, sizeof(expected), ssid);
  UTIL1_strcat(expected, sizeof(expected), "\",\"");
  UTIL1_strcat(expected, sizeof(expected), pwd);
  UTIL1_strcat(expected, sizeof(expected), "\"\r\r\n\r\nOK\r\n");
  
  returnESP_SendATCommand(txBuf, rxBuf, sizeof(rxBuf), expected, ESP_DEFAULT_TIMEOUT_MS, io);
}
  
uint8_t ESP_JoinAP(constuint8_t *ssid, constuint8_t *pwd, intnofRetries, CLS1_ConstStdIOType *io) {
  uint8_t buf[32];
  uint8_t res;
  
  do{
    res = JoinAccessPoint(ssid, pwd, io);
    if(res==ERR_OK) {
      break;
    }
    WAIT1_WaitOSms(1000);
    nofRetries--;
  } while(nofRetries>0);
  returnres;
}
  
staticuint8_t ReadIntoIPDBuffer(uint8_t *buf, size_t bufSize, uint8_t *p, uint16_t msgSize, uint16_t msTimeout, constCLS1_StdIOType *io) {
  uint8_t ch;
  size_t nofInBuf;
  inttimeout;
  
  nofInBuf = p-buf;
  bufSize -= nofInBuf; /* take into account what we already have in buffer */
  timeout = msTimeout;
  while(msgSize>0&& bufSize>0) {
    if(AS2_GetCharsInRxBuf()>0) {
      (void)AS2_RecvChar(&ch);
      *p = ch;
      if(io!=NULL) { /* copy on console */
        io->stdOut(ch);
      }
      p++;
      *p = '\0'; /* terminate */
      nofInBuf++; msgSize--; bufSize--;
    } else{
      /* check in case we recveive less characters than expected, happens for POST? */
      if(nofInBuf>6&& UTIL1_strncmp(&p[-6], "\r\nOK\r\n", sizeof("\r\nOK\r\n")-1)==0) {
        break;
      } else{
        timeout -= 10;
        WAIT1_WaitOSms(10);
        if(timeout<0) {
          returnERR_BUSY;
        }
      }
    }
  }
  returnERR_OK;
}
  
uint8_t ESP_GetIPD(uint8_t *msgBuf, size_t msgBufSize, uint8_t *ch_id, uint16_t *size, bool *isGet, uint16_t timeoutMs, constCLS1_StdIOType *io) {
  /* scan e.g. for
   * +IPD,0,404:POST / HTTP/1.1
   * and return ch_id (0), size (404)
   */
  uint8_t res = ERR_OK;
  constuint8_t *p;
  bool isIPD = FALSE;
  uint8_t cmd[24], rxBuf[48];
  uint16_t ipdSize;
  
  *ch_id = 0; *size = 0; *isGet = FALSE; /* init */
  for(;;) { /* breaks */
    res = ESP_ReadCharsUntil(msgBuf, msgBufSize, '\n', timeoutMs);
    if(res!=ERR_OK) {
      break; /* timeout */
    }
    if(res==ERR_OK) { /* line read */
      if(io!=NULL) {
        CLS1_SendStr(msgBuf, io->stdOut); /* copy on console */
      }
      isIPD = UTIL1_strncmp(msgBuf, "+IPD,", sizeof("+IPD,")-1)==0;
      if(isIPD) { /* start of IPD message */
        p = msgBuf+sizeof("+IPD,")-1;
        if(UTIL1_ScanDecimal8uNumber(&p, ch_id)!=ERR_OK) {
          if(io!=NULL) {
            CLS1_SendStr("ERR: wrong channel?\r\n", io->stdErr); /* error on console */
          }
          res = ERR_FAILED;
          break;
        }
        if(*p!=',') {
          res = ERR_FAILED;
          break;
        }
        p++; /* skip comma */
        if(UTIL1_ScanDecimal16uNumber(&p, size)!=ERR_OK) {
          if(io!=NULL) {
            CLS1_SendStr("ERR: wrong size?\r\n", io->stdErr); /* error on console */
          }
          res = ERR_FAILED;
          break;
        }
        if(*p!=':') {
          res = ERR_FAILED;
          break;
        }
        ipdSize = p-msgBuf; /* length of "+IPD,<channel>,<size>" string */
        p++; /* skip ':' */
        if(UTIL1_strncmp(p, "GET", sizeof("GET")-1)==0) {
          *isGet = TRUE;
        } elseif(UTIL1_strncmp(p, "POST", sizeof("POST")-1)==0) {
          *isGet = FALSE;
        } else{
          res = ERR_FAILED;
        }
        while(*p!='\0') {
          p++; /* skip to the end */
        }
        /* read the rest of the message */
        res = ReadIntoIPDBuffer(msgBuf, msgBufSize, (uint8_t*)p, (*size)-ipdSize, ESP_DEFAULT_TIMEOUT_MS, io);
        break;
      }
    }
  }
  returnres;
}
  
uint8_t ESP_StartWebServer(constCLS1_StdIOType *io) {
  uint8_t buf[32];
  uint8_t res;
  
  res = ESP_SetNumberOfConnections(1, io, ESP_DEFAULT_TIMEOUT_MS);
  if(res!=ERR_OK) {
    CLS1_SendStr("ERR: failed to set multiple connections.\r\n", io->stdErr);
    returnres;
  }
  res = ESP_SetServer(TRUE, 80, io, ESP_DEFAULT_TIMEOUT_MS);
  if(res!=ERR_OK) {
    CLS1_SendStr("ERR: failed to set server.\r\n", io->stdErr);
    returnres;
  }
  CLS1_SendStr("INFO: Web Server started, waiting for connection on ", io->stdOut);
  if(ESP_GetIPAddrString(buf, sizeof(buf))==ERR_OK) {
    CLS1_SendStr(buf, io->stdOut);
    CLS1_SendStr(":80", io->stdOut);
  } else{
    CLS1_SendStr("(ERROR!)", io->stdOut);
  }
  CLS1_SendStr("\r\n", io->stdOut);
  
  returnERR_OK;
}
  
uint8_t ESP_SendStr(constuint8_t *str, CLS1_ConstStdIOType *io) {
  uint8_t buf[32];
  uint8_t rxBuf[48];
  uint8_t res;
  uint16_t timeoutMs;
  #define RX_TIMEOUT_MS 3000
  AS2_TComData ch;
  
  UTIL1_strcpy(buf, sizeof(buf), str);
  UTIL1_strcat(buf, sizeof(buf), "\r\n");
  res = ESP_SendATCommand(buf, rxBuf, sizeof(rxBuf), NULL, ESP_DEFAULT_TIMEOUT_MS, io);
  timeoutMs = 0;
  while(timeoutMs<RX_TIMEOUT_MS) {
    WAIT1_WaitOSms(100);
    timeoutMs += 100;
    while(AS2_GetCharsInRxBuf()>0) {
      (void)AS2_RecvChar(&ch);
      CLS1_SendChar(ch);
    }
  }
  returnERR_OK;
}
  
staticuint8_t ESP_PrintHelp(constCLS1_StdIOType *io) {
  CLS1_SendHelpStr("ESP", "ESP8200 commands\r\n", io->stdOut);
  CLS1_SendHelpStr("  help|status", "Print help or status information\r\n", io->stdOut);
  CLS1_SendHelpStr("  send <str>", "Sends a string to the module\r\n", io->stdOut);
  CLS1_SendHelpStr("  test", "Sends a test AT command\r\n", io->stdOut);
  CLS1_SendHelpStr("  restart", "Restart module\r\n", io->stdOut);
  CLS1_SendHelpStr("  listAP", "List available Access Points\r\n", io->stdOut);
  CLS1_SendHelpStr("  connectAP \"ssid\",\"pwd\"", "Connect to an Access Point\r\n", io->stdOut);
  CLS1_SendHelpStr("  server (start|stop)", "Start or stop web server\r\n", io->stdOut);
  returnERR_OK;
}
  
staticuint8_t ESP_PrintStatus(constCLS1_StdIOType *io) {
  uint8_t buf[48];
  
  CLS1_SendStatusStr("ESP8266", "\r\n", io->stdOut);
  
  CLS1_SendStatusStr("  Webserver", ESP_WebServerIsOn?"ON\r\n":"OFF\r\n", io->stdOut);
  
  if(ESP_GetFirmwareVersionString(buf, sizeof(buf)) != ERR_OK) {
    UTIL1_strcpy(buf, sizeof(buf), "FAILED\r\n");
  } else{
    UTIL1_strcat(buf, sizeof(buf), "\r\n");
  }
  CLS1_SendStatusStr("  AT+GMR", buf, io->stdOut);
  
  if(ESP_GetModeString(buf, sizeof(buf)) != ERR_OK) {
    UTIL1_strcpy(buf, sizeof(buf), "FAILED\r\n");
  } else{
    if(UTIL1_strcmp(buf, "1")==0) {
      UTIL1_strcat(buf, sizeof(buf), " (device)");
    } elseif(UTIL1_strcmp(buf, "2")==0) {
      UTIL1_strcat(buf, sizeof(buf), " (AP)");
    } elseif(UTIL1_strcmp(buf, "3")==0) {
      UTIL1_strcat(buf, sizeof(buf), " (device+AP)");
    } else{
      UTIL1_strcat(buf, sizeof(buf), " (ERROR)");
    }
    UTIL1_strcat(buf, sizeof(buf), "\r\n");
  }
  CLS1_SendStatusStr("  AT+CWMODE?", buf, io->stdOut);
  
  if(ESP_GetIPAddrString(buf, sizeof(buf)) != ERR_OK) {
    UTIL1_strcpy(buf, sizeof(buf), "FAILED\r\n");
  } else{
    UTIL1_strcat(buf, sizeof(buf), "\r\n");
  }
  CLS1_SendStatusStr("  AT+CIFSR", buf, io->stdOut);
  
  if(ESP_GetConnectedAPString(buf, sizeof(buf)) != ERR_OK) {
    UTIL1_strcpy(buf, sizeof(buf), "FAILED\r\n");
  } else{
    UTIL1_strcat(buf, sizeof(buf), "\r\n");
  }
  CLS1_SendStatusStr("  AT+CWJAP?", buf, io->stdOut);
  
  if(ESP_GetCIPMUXString(buf, sizeof(buf)) != ERR_OK) {
    UTIL1_strcpy(buf, sizeof(buf), "FAILED\r\n");
  } else{
    if(UTIL1_strcmp(buf, "0")==0) {
      UTIL1_strcat(buf, sizeof(buf), " (single connection)");
    } elseif(UTIL1_strcmp(buf, "1")==0) {
      UTIL1_strcat(buf, sizeof(buf), " (multiple connections)");
    } else{
      UTIL1_strcat(buf, sizeof(buf), " (ERROR)");
    }
    UTIL1_strcat(buf, sizeof(buf), "\r\n");
  }
  CLS1_SendStatusStr("  CIPMUX", buf, io->stdOut);
  returnERR_OK;
}
  
uint8_t ESP_ParseCommand(constunsigned char*cmd, bool *handled, constCLS1_StdIOType *io) {
  uint32_t val;
  uint8_t res;
  constunsigned char*p;
  uint8_t pwd[24], ssid[24];
  
  if(UTIL1_strcmp((char*)cmd, CLS1_CMD_HELP)==0|| UTIL1_strcmp((char*)cmd, "ESP help")==0) {
    *handled = TRUE;
    res = ESP_PrintHelp(io);
  } elseif(UTIL1_strcmp((char*)cmd, CLS1_CMD_STATUS)==0|| UTIL1_strcmp((char*)cmd, "ESP status")==0) {
    *handled = TRUE;
    res = ESP_PrintStatus(io);
  } elseif(UTIL1_strncmp((char*)cmd, "ESP send ", sizeof("ESP send ")-1)==0) {
    *handled = TRUE;
    p = cmd+sizeof("ESP send ")-1;
  
    (void)ESP_SendStr(p, io);
  } elseif(UTIL1_strcmp((char*)cmd, "ESP test")==0) {
    *handled = TRUE;
    if(ESP_TestAT()!=ERR_OK) {
      CLS1_SendStr("TEST failed!\r\n", io->stdErr);
      res = ERR_FAILED;
    } else{
      CLS1_SendStr("TEST ok!\r\n", io->stdOut);
    }
  } elseif(UTIL1_strcmp((char*)cmd, "ESP listAP")==0) {
    *handled = TRUE;
    (void)ESP_SendStr("AT+CWLAP", io);
    /* AT + CWLAP
    response
    + CWLAP: <ecn>, <ssid>, <rssi> [, <mode>]
    OK Or Fails, the return ERROR
    <Ecn> 0 OPEN
    1 WEP
    2 WPA_PSK
    3 WPA2_PSK
    4 WPA_WPA2_PSK
    <Ssid> string parameter, the access point name
    <Rssi> signal strength
    <Mode> 0: manually connect 1: An automatic connection
     */
    returnERR_OK;
  } elseif(UTIL1_strncmp((char*)cmd, "ESP connectAP ", sizeof("ESP connectAP ")-1)==0) {
    *handled = TRUE;
    p = cmd+sizeof("ESP connectAP ")-1;
    ssid[0] = '\0'; pwd[0] = '\0';
    res = UTIL1_ScanDoubleQuotedString(&p, ssid, sizeof(ssid));
    if(res==ERR_OK && *p!='\0'&& *p==',') {
      p++; /* skip comma */
      res = UTIL1_ScanDoubleQuotedString(&p, pwd, sizeof(pwd));
    } else{
      CLS1_SendStr("Comma expected between strings!\r\n", io->stdErr);
      res = ERR_FAILED;
    }
    if(res==ERR_OK) {
      res = ESP_JoinAP(ssid, pwd, 3, io);
    } else{
      CLS1_SendStr("Wrong command format!\r\n", io->stdErr);
      res = ERR_FAILED;
    }
  } elseif(UTIL1_strcmp((char*)cmd, "ESP server start")==0) {
    *handled = TRUE;
    res = ESP_StartWebServer(io);
    ESP_WebServerIsOn = res==ERR_OK;
  } elseif(UTIL1_strcmp((char*)cmd, "ESP server stop")==0) {
    *handled = TRUE;
    ESP_WebServerIsOn = FALSE;
  } elseif(UTIL1_strcmp((char*)cmd, "ESP restart")==0) {
    *handled = TRUE;
    ESP_Restart(io, 2000);
  }
  returnres;
}
  
voidESP_Deinit(void) {
  /* nothing to do */
}
  
voidESP_Init(void) {
  AS2_ClearRxBuf(); /* clear buffer */
}

The application interface in Application.h is rather short :-):

/*
 * Application.h
 *
 *      Author: Erich Styger
 */
  
#ifndef APPLICATION_H_
#define APPLICATION_H_
  
/*!
 * \brief Application main routine
 */
voidAPP_Run(void);
  
#endif /* APPLICATION_H_ */

The main loop of the application is Application.c, along with the application specific web server code.

As the SendWebPage function contains HTML code, I’m posting it here separately:

staticuint8_t SendWebPage(uint8_t ch_id, bool ledIsOn, uint8_t temperature, constCLS1_StdIOType *io) {
  staticuint8_t http[1024];
  uint8_t cmd[24], rxBuf[48], expected[48];
  uint8_t buf[16];
  uint8_t res = ERR_OK;
  
  /* construct web page content */
  UTIL1_strcpy(http, sizeof(http), (uint8_t*)"HTTP/1.0 200 OK\r\nContent-Type: text/html\r\nPragma: no-cache\r\n\r\n");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"<html>\r\n<body>\r\n");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"<title>ESP8266 Web Server</title>\r\n");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"<h2>Web Server using ESP8266</h2>\r\n");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"
<hr>\r\n");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"<p><form method=\"POST\"><strong>Temp: <input type=\"text\" size=2 value=\"");
  UTIL1_strcatNum8s(http, sizeof(http), temperature);
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"\"> <sup>O</sup>C");
  if(ledIsOn) {
    UTIL1_strcat(http, sizeof(http), (uint8_t*)"<p><input type=\"radio\" name=\"radio\" value=\"0\" >Red LED off");
    UTIL1_strcat(http, sizeof(http), (uint8_t*)"
<input type=\"radio\" name=\"radio\" value=\"1\" checked>Red LED on");
  } else{
    UTIL1_strcat(http, sizeof(http), (uint8_t*)"<p><input type=\"radio\" name=\"radio\" value=\"0\" checked>Red LED off");
    UTIL1_strcat(http, sizeof(http), (uint8_t*)"
<input type=\"radio\" name=\"radio\" value=\"1\" >Red LED on");
  }
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"</strong><p><input type=\"submit\"></form></span>");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"</body>\r\n</html>\r\n");
  
  UTIL1_strcpy(cmd, sizeof(cmd), "AT+CIPSEND="); /* parameters are <ch_id>,<size> */
  UTIL1_strcatNum8u(cmd, sizeof(cmd), ch_id);
  UTIL1_chcat(cmd, sizeof(cmd), ',');
  UTIL1_strcatNum16u(cmd, sizeof(cmd), UTIL1_strlen(http));
  UTIL1_strcpy(expected, sizeof(expected), cmd); /* we expect the echo of our command */
  UTIL1_strcat(expected, sizeof(expected), "\r\r\n> "); /* expect "> " */
  UTIL1_strcat(cmd, sizeof(cmd), "\r\n");
  res = ESP_SendATCommand(cmd, rxBuf, sizeof(rxBuf), expected, ESP_DEFAULT_TIMEOUT_MS, io);
  if(res!=ERR_OK) {
    if(io!=NULL) {
      CLS1_SendStr("INFO: TIMEOUT, closing connection!\r\n", io->stdOut);
    }
  } else{
    if(io!=NULL) {
      CLS1_SendStr("INFO: Sending http page...\r\n", io->stdOut);
    }
    UTIL1_strcat(http, sizeof(http), "\r\n\r\n"); /* need to add this to end the command! */
    res = ESP_SendATCommand(http, NULL, 0, NULL, ESP_DEFAULT_TIMEOUT_MS, io);
    if(res!=ERR_OK) {
      CLS1_SendStr("Sending page failed!\r\n", io->stdErr); /* copy on console */
    } else{
      for(;;) { /* breaks */
        res = ESP_ReadCharsUntil(buf, sizeof(buf), '\n', 1000);
        if(res==ERR_OK) { /* line read */
          if(io!=NULL) {
            CLS1_SendStr(buf, io->stdOut); /* copy on console */
          }
        }
        if(UTIL1_strncmp(buf, "SEND OK\r\n", sizeof("SEND OK\r\n")-1)==0) { /* ok from module */
          break;
        }
      }
    }
  }
  returnres;
}

The rest of Application.c is rather simple:

/*
 * Application.c
 *
 *      Author: Erich Styger
 */
#include "PE_Types.h"
#include "CLS1.h"
#include "WAIT1.h"
#include "Shell.h"
#include "UTIL1.h"
#include "ESP8266.h"
#include "LEDR.h"
#include "LEDG.h"
#include "AS2.h"
  
staticuint8_t APP_EspMsgBuf[512]; /* buffer for messages from ESP8266 */
  
staticvoidWebProcess(void) {
  uint8_t res=ERR_OK;
  bool isGet;
  uint8_t ch_id=0;
  uint16_t size=0;
  constuint8_t *p;
  constCLS1_StdIOType *io;
  
  if(ESP_IsServerOn()) {
    io = CLS1_GetStdio();
    res = ESP_GetIPD(APP_EspMsgBuf, sizeof(APP_EspMsgBuf), &ch_id, &size, &isGet, 1000, io);
    if(res==ERR_OK) {
      if(isGet) { /* GET: put web page */
        res = SendWebPage(ch_id, LEDR_Get()!=FALSE, 21/*dummy temperature*/, io);
        if(res!=ERR_OK && io!=NULL) {
          CLS1_SendStr("Sending page failed!\r\n", io->stdErr); /* copy on console */
        }
      } else{ /* POST: received info */
        intpos;
  
        pos = UTIL1_strFind(APP_EspMsgBuf, "radio=");
        if(pos!=-1) { /* found */
          if(UTIL1_strncmp(&APP_EspMsgBuf[pos], "radio=0", sizeof("radio=0")-1)) {
            LEDR_On();
          } elseif(UTIL1_strncmp(&APP_EspMsgBuf[pos], "radio=1", sizeof("radio=1")-1)) {
            LEDR_Off();
          }
        }
        res = SendWebPage(ch_id, LEDR_Get()!=FALSE, 20/*dummy temperature*/, io);
        if(res!=ERR_OK && io!=NULL) {
          CLS1_SendStr("Sending page failed!\r\n", io->stdErr); /* copy on console */
        }
      }
      CLS1_SendStr("INFO: Closing connection...\r\n", io->stdOut);
      res = ESP_CloseConnection(ch_id, io, ESP_DEFAULT_TIMEOUT_MS);
    }
  } else{ /* copy messages we receive to console */
    while(AS2_GetCharsInRxBuf()>0) {
      uint8_t ch;
  
      (void)AS2_RecvChar(&ch);
      CLS1_SendChar(ch);
    }
  }
}
  
voidAPP_Run(void) {
  CLS1_ConstStdIOType *io;
  
  WAIT1_Waitms(1000); /* wait after power-on */
  ESP_Init();
  SHELL_Init();
  io = CLS1_GetStdio();
  CLS1_SendStr("\r\n------------------------------------------\r\n", io->stdOut);
  CLS1_SendStr("ESP8266 with FRDM-KL25Z\r\n", io->stdOut);
  CLS1_SendStr("------------------------------------------\r\n", io->stdOut);
  CLS1_PrintPrompt(io);
  for(;;) {
    WebProcess();
    SHELL_Parse();
    WAIT1_Waitms(10);
    LEDG_Neg();
  }
}

In main.c I call the application part:

/* ###################################################################
**     Filename    : main.c
**     Project     : FRDM-KL25Z_ESP8266
**     Processor   : MKL25Z128VLK4
**     Version     : Driver 01.01
**     Compiler    : GNU C Compiler
**     Date/Time   : 2014-10-15, 14:28, # CodeGen: 0
**     Abstract    :
**         Main module.
**         This module contains user's application code.
**     Settings    :
**     Contents    :
**         No public methods
**
** ###################################################################*/
/*!
** @file main.c
** @version 01.01
** @brief
**         Main module.
**         This module contains user's application code.
*/        
/*!
**  @addtogroup main_module main module documentation
**  @{
*/        
/* MODULE main */
  
/* Including needed modules to compile this module/procedure */
#include "Cpu.h"
#include "Events.h"
#include "WAIT1.h"
#include "UTIL1.h"
#include "AS1.h"
#include "ASerialLdd1.h"
#include "CLS1.h"
#include "CS1.h"
#include "AS2.h"
#include "ASerialLdd2.h"
#include "LEDR.h"
#include "LEDpin1.h"
#include "BitIoLdd1.h"
#include "LEDG.h"
#include "LEDpin2.h"
#include "BitIoLdd2.h"
#include "LEDB.h"
#include "LEDpin3.h"
#include "BitIoLdd3.h"
/* Including shared modules, which are used for whole project */
#include "PE_Types.h"
#include "PE_Error.h"
#include "PE_Const.h"
#include "IO_Map.h"
/* User includes (#include below this line is not maintained by Processor Expert) */
#include "Application.h"
  
/*lint -save  -e970 Disable MISRA rule (6.3) checking. */
intmain(void)
/*lint -restore Enable MISRA rule (6.3) checking. */
{
  /* Write your local variable definition here */
  
  /*** Processor Expert internal initialization. DON'T REMOVE THIS CODE!!! ***/
  PE_low_level_init();
  /*** End of Processor Expert internal initialization.                    ***/
  
  APP_Run();
  
  /*** Don't write any code pass this line, or it will be deleted during code generation. ***/
  /*** RTOS startup code. Macro PEX_RTOS_START is defined by the RTOS component. DON'T MODIFY THIS CODE!!! ***/
  #ifdef PEX_RTOS_START
    PEX_RTOS_START();                  /* Startup of the selected RTOS. Macro is defined by the RTOS component. */
  #endif
  /*** End of RTOS startup code.  ***/
  /*** Processor Expert end of main routine. DON'T MODIFY THIS CODE!!! ***/
  for(;;){}
  /*** Processor Expert end of main routine. DON'T WRITE CODE BELOW!!! ***/
} /*** End of main routine. DO NOT MODIFY THIS TEXT!!! ***/
  
/* END main */
/*!
** @}
*/
/*
** ###################################################################
**
**     This file was created by Processor Expert 10.4 [05.10]
**     for the Freescale Kinetis series of microcontrollers.
**
** ###################################################################
*/

Processor Expert Components

In addition, I’m using several Processor Expert component which are available fromSourceForge.

Processor Expert Components

Wait: Busy waiting component, e.g. to wait for a few milliseconds.
Utility: string manipulation and utility functions.
AsynchroSerial (AS1): serial interface to the host for the shell command line interface
Shell: command line shell implementation
CriticalSection: for creating critical sections
AsynchroSerial (AS2): serial interface to the ESP8266 module
LEDR, LEDG and LEDB: Red, Green and Blue LED on the FRDM-KL25Z board

AS1 is configured as UART connection (over OpenSDA) for the shell:

Shell UART Settings

There are no special settings for the Shell component:

Shell Settings

Important are the correct settings to the ESP8266 UART: 115200 baud and using the correct pins on the board connected to the Rx and Tx lines of the ESP8266. I’m using rather large input and output buffers:

UART connection to ESP8266

The LED components are configured for the pins used on the board: PTB18 for red, PTB19 for green and PTD1 for blue LED.

Red LED for FRDM-KL25Z

Sending Commands

The shell implements the command ESP send which I can use to send a string or command to the module:

ESP send <str>

Note that for every command a trailing “\r\n” will be sent.

So instead of using the programmatic way, the shell can be used to ‘manually’ drive a web server, at least most of the part. So I’m using command line commands below to explore how the ESP8266 module works.

Using the Shell

With the project (link to GitHub below), I have a serial connection and command line shell interface to the module. Compile the project and download it to the FRDM-KL25Z board and use a terminal program (I use Termite) to talk with the module.

It power-up, the program shows a greeting message:

Greeting Message

With ‘help‘ I get a list of the available commands:

Help Command

The ‘status‘ command gives a system status:

Status Command Output

With this, I’m ready to send commands to the module :-).

Connection Test

To test the connection I send a simple ‘AT’ command

ESP send AT

AT Command Output

and the module should respond with

AT\r\r\n\r\nOK\r\n

Module Restart

Sometimes the module gets stuck. What helps is a power-on reset of the module. Another way is to send the

AT+RST

command to reset the module. The module will boot up and print a ‘ready’ message:

Reset of the ESP8266

Access Point or Device

First I need to configure if the ESP is either a device or an access point. For this, theCWMODE command is used:

AT+CWMODE=

where <mode> is one of:

1: ‘Sta’, ESP8266 is a device, it connects to an existing access point
2: ‘AP’, ESP8266 is an access point, so other devices can connect to it
3: ‘both’. Not really clear to me, but it seems that in this mode the device is in a hybrid mode?

To have the ESP as device so it can connect to an existing access point I use

AT+CWMODE=1

and the module should answer with

AT+CWMODE=1\r\r\n\r\nOK\r\n

or with a ‘no change':

AT+CWMODE=1\r\r\nno change\r\n

With

AT+CWMODE?

I can ask for the current mode:

Retrieving Current Mode

List of Access Points

With

AT+CWLAP

I get a list of access points. It reports a list like this:

AT+CWLAP




+CWLAP:(0,"",0)
+CWLAP:(4,"APforESP",-39)
+CWLAP:(4,"iza-97497",-94)




OK

:!: I experienced problems with that command in an environment with lots of access points visible. In this case it seems the module hands up. Try first in a place with only a few access points.

For this tutorial I have configured an access point with SSID “APforESP” which shows up in my list.

The list is formatted like this

+ CWLAP: , , [, ]

With following encoding:

<ecn>:

0: OPEN
1: WPA_PSK
2: WPA2_PSK
4: WPA_WPA2_PSK

<ssid>: the SSID (string) of the access point.

<rssi>: Signal strength.

<mode>:

0: manually connect
1: automatic connect

Connecting to Access Point

To connect to an access point I use the command

AT+CWJAP="<ssid>","<pwd>"

Of course replace and with your setup. The module should report back an “OK” message, and you are connected :-).

:!: The module stores the ssid and password. After power-up, the module will automatically reconnect to the Access Point.

IP Address

Once connected I can check the IP address I have been assigned to with

AT+CIFSR

which should give something like

AT+CIFSR




192.168.0.111

So now I know my module IP address :-). With this I can ping my module:

Pinging my ESP Module

Building a Web Server

Now as we hav a connection, it is time to use it to run a web server :-).What I want to serve a web page which I can use to turn on or off the LEDs on the board.

Number of Connections: CIPMUX

Before I start the server I need to make sure it accepts multiple connections. For this I use the following command:

AT+CIPMUX=1

The parameter is either 0 (single connection), or 1 (multiple connections). For a web server I need to set it up for multiple connections.

The ESP module should respond with

AT+CIPMUX=1\r\n\r\nOK\r\n

:info: To make it clear, I have included the ‘\r’ and ‘\n’ in the responses.

Starting the Server: CIPSERVER

I start the server with

AT+CIPSERVER=1,80

The first parameter is either 0 (close connection) or 1 (open connection), followed by the port. I use here the standard http port (80).

The module should answer with:

AT+CIPSERVER=1,80\r\r\n\r\nOK\r\n

or if it is already running the server with a ‘no change':

AT+CIPSERVER=1,80\r\r\nno change\r\n

No I have a connection open on my IP address (see above: 192.168.0.111), listening to the port I have specified (80).

Connecting to the Server with Browser

I enter the IP address in a web browser:

http://192.168.0.111:80

For clarity I have specified the standard HTTP port (80). So if you are using a different port, make sure you specify it in the address line.

Connection from FireFox

The browser now sends a GET request to the module, and I will see this from the message printed out from the module:

First response from Module

The ‘Link’ indicates that it has established a link. IPD (IP Data?) is followed by the channel number (this will the one we have to respond to), plus the size of the following data (296 bytes in that case).

As I’m not responding (yet), there will be a timeout (after about 1 minute or so), with an ‘Unlink’ message from the module:

Link




+IPD,0,296:GET / HTTP/1.1
Host: 192.168.0.111
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:33.0) Gecko/20100101 Firefox/33.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: de,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: keep-alive
OK
Unlink

Unlink message

Sending Data to Server: CIPSEND

Now I need to respond and send data to the browser. For this I need to know the channel number, and this is provided in the IPD message from above, right after the comma:

 +IPD,0

To send data, I use the command

AT+CIPSEND=<channel>,<size>

So I connect again with the browser, and I send 5 bytes (“hello”) with:

AT+CIPSEND=0,5

The ESP8266 responds with

AT+CIPSEND=0,5\r\n>

Notice the ‘>’ at the end: this is my signal to send the actual data (“hello” in my case):

hello

The ESP8266 now resonds with a SEND OK:

Data Sent

However, the browser is still busy and spins around. I already thought that I did something wrong, but after the browser run into a timeout (after about one minute), my data is there! :-)

Hello in Browser

Closing Connection: CIPCLOSE

So things *are* working :-). The trick is that I have to close the connection after I have sent the data. There is a CIPCLOSE command I can use:

AT+CIPCLOSE=<channel>

which I can use to close a channel. So I close the connection with

AT+CIPCLOSE=0

and now the browser shows the content right away :-).

Web Server Implementation

So far I have used the module in command line and manual mode. This is great for exploration of the protocol, but for building the web server I need to do this programmatically. For this I run my ‘main’ loop in APP_Run(). After printing a greeting message and initializing the sub modules, it processes the web/module responses, parses the shell command line interfaces and blinks the green (LEDG) LED.

voidAPP_Run(void) {
  CLS1_ConstStdIOType *io;
  
  WAIT1_Waitms(1000); /* wait after power-on */
  ESP_Init();
  SHELL_Init();
  io = CLS1_GetStdio();
  CLS1_SendStr("\r\n------------------------------------------\r\n", io->stdOut);
  CLS1_SendStr("ESP8266 with FRDM-KL25Z\r\n", io->stdOut);
  CLS1_SendStr("------------------------------------------\r\n", io->stdOut);
  CLS1_PrintPrompt(io);
  for(;;) {
    WebProcess();
    SHELL_Parse();
    WAIT1_Waitms(10);
    LEDG_Neg();
  }
}

With

ESP server start

I start the web server:

Starting the Web Server

It sends the AT+CIPMUX command followed by the AT+CIPSERVER to start the server, and then listens to the port. Reading and responding messages is done in WebProcess():

staticvoidWebProcess(void) {
  uint8_t res=ERR_OK;
  bool isGet;
  uint8_t ch_id=0;
  uint16_t size=0;
  constuint8_t *p;
  constCLS1_StdIOType *io;
  
  if(ESP_IsServerOn()) {
    io = CLS1_GetStdio();
    res = ESP_GetIPD(APP_EspMsgBuf, sizeof(APP_EspMsgBuf), &ch_id, &size, &isGet, 1000, io);
    if(res==ERR_OK) {
      if(isGet) { /* GET: put web page */
        res = SendWebPage(ch_id, LEDR_Get()!=FALSE, 21/*dummy temperature*/, io);
        if(res!=ERR_OK && io!=NULL) {
          CLS1_SendStr("Sending page failed!\r\n", io->stdErr); /* copy on console */
        }
      } else{ /* POST: received info */
        intpos;
  
        pos = UTIL1_strFind(APP_EspMsgBuf, "radio=");
        if(pos!=-1) { /* found */
          if(UTIL1_strncmp(&APP_EspMsgBuf[pos], "radio=0", sizeof("radio=0")-1)) {
            LEDR_On();
          } elseif(UTIL1_strncmp(&APP_EspMsgBuf[pos], "radio=1", sizeof("radio=1")-1)) {
            LEDR_Off();
          }
        }
        res = SendWebPage(ch_id, LEDR_Get()!=FALSE, 20/*dummy temperature*/, io);
        if(res!=ERR_OK && io!=NULL) {
          CLS1_SendStr("Sending page failed!\r\n", io->stdErr); /* copy on console */
        }
      }
      CLS1_SendStr("INFO: Closing connection...\r\n", io->stdOut);
      res = ESP_CloseConnection(ch_id, io, ESP_DEFAULT_TIMEOUT_MS);
    }
  } else{ /* copy messages we receive to console */
    while(AS2_GetCharsInRxBuf()>0) {
      uint8_t ch;
  
      (void)AS2_RecvChar(&ch);
      CLS1_SendChar(ch);
    }
  }
}

If the server is not enabled, it simply copies the received messages to the console:

} else{ /* copy messages we receive to console */
   while(AS2_GetCharsInRxBuf()>0) {
     uint8_t ch;
 
     (void)AS2_RecvChar(&ch);
     CLS1_SendChar(ch);
   }
 }

Otherwise it scans for an IPD message (ESP_GetIPD()). This function returns the whole message, the channel, the message size and if it is a GET or POST message:

1	`res = ESP_GetIPD(APP_EspMsgBuf, sizeof(APP_EspMsgBuf), &ch_id, &size, &isGet, 1000, io);`

If it is a GET message, then it sends a HTML page to the module:

1	`res = SendWebPage(ch_id, LEDR_Get()!=FALSE, 21 /dummy temperature/, io);`

This web page shows the status of the red LED on the board, a (dummy) temperature value and a button to submit new LED values:

WSP8266 Web Server

The HTML code for this page is constructed in SendWebPage() and sent withAT+CIPSEND:

staticuint8_t SendWebPage(uint8_t ch_id, bool ledIsOn, uint8_t temperature, constCLS1_StdIOType *io) {
  staticuint8_t http[1024];
  uint8_t cmd[24], rxBuf[48], expected[48];
  uint8_t buf[16];
  uint8_t res = ERR_OK;
  
  /* construct web page content */
  UTIL1_strcpy(http, sizeof(http), (uint8_t*)"HTTP/1.0 200 OK\r\nContent-Type: text/html\r\nPragma: no-cache\r\n\r\n");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"<html>\r\n<body>\r\n");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"<title>ESP8266 Web Server</title>\r\n");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"<h2>Web Server using ESP8266</h2>\r\n");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"
<hr>\r\n");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"<p><form method=\"POST\"><strong>Temp: <input type=\"text\" size=2 value=\"");
  UTIL1_strcatNum8s(http, sizeof(http), temperature);
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"\"> <sup>O</sup>C");
  if(ledIsOn) {
    UTIL1_strcat(http, sizeof(http), (uint8_t*)"<p><input type=\"radio\" name=\"radio\" value=\"0\" >Red LED off");
    UTIL1_strcat(http, sizeof(http), (uint8_t*)"
<input type=\"radio\" name=\"radio\" value=\"1\" checked>Red LED on");
  } else{
    UTIL1_strcat(http, sizeof(http), (uint8_t*)"<p><input type=\"radio\" name=\"radio\" value=\"0\" checked>Red LED off");
    UTIL1_strcat(http, sizeof(http), (uint8_t*)"
<input type=\"radio\" name=\"radio\" value=\"1\" >Red LED on");
  }
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"</strong><p><input type=\"submit\"></form></span>");
  UTIL1_strcat(http, sizeof(http), (uint8_t*)"</body>\r\n</html>\r\n");
  
  UTIL1_strcpy(cmd, sizeof(cmd), "AT+CIPSEND="); /* parameters are <ch_id>,<size> */
  UTIL1_strcatNum8u(cmd, sizeof(cmd), ch_id);
  UTIL1_chcat(cmd, sizeof(cmd), ',');
  UTIL1_strcatNum16u(cmd, sizeof(cmd), UTIL1_strlen(http));
  UTIL1_strcpy(expected, sizeof(expected), cmd); /* we expect the echo of our command */
  UTIL1_strcat(expected, sizeof(expected), "\r\r\n> "); /* expect "> " */
  UTIL1_strcat(cmd, sizeof(cmd), "\r\n");
  res = ESP_SendATCommand(cmd, rxBuf, sizeof(rxBuf), expected, ESP_DEFAULT_TIMEOUT_MS, io);
  if(res!=ERR_OK) {
    if(io!=NULL) {
      CLS1_SendStr("INFO: TIMEOUT, closing connection!\r\n", io->stdOut);
    }
  } else{
    if(io!=NULL) {
      CLS1_SendStr("INFO: Sending http page...\r\n", io->stdOut);
    }
    UTIL1_strcat(http, sizeof(http), "\r\n\r\n"); /* need to add this to end the command! */
    res = ESP_SendATCommand(http, NULL, 0, NULL, ESP_DEFAULT_TIMEOUT_MS, io);
    if(res!=ERR_OK) {
      CLS1_SendStr("Sending page failed!\r\n", io->stdErr); /* copy on console */
    } else{
      for(;;) { /* breaks */
        res = ESP_ReadCharsUntil(buf, sizeof(buf), '\n', 1000);
        if(res==ERR_OK) { /* line read */
          if(io!=NULL) {
            CLS1_SendStr(buf, io->stdOut); /* copy on console */
          }
        }
        if(UTIL1_strncmp(buf, "SEND OK\r\n", sizeof("SEND OK\r\n")-1)==0) { /* ok from module */
          break;
        }
      }
    }
  }
  returnres;
}

In case of a POST message (user has pressed the button), I scan for the radio element string and turn on/off the LED accordingly, and re-submit the new web page:

} else{ /* POST: received info */
      intpos;
 
      pos = UTIL1_strFind(APP_EspMsgBuf, "radio=");
      if(pos!=-1) { /* found */
        if(UTIL1_strncmp(&APP_EspMsgBuf[pos], "radio=0", sizeof("radio=0")-1)) {
          LEDR_On();
        } elseif(UTIL1_strncmp(&APP_EspMsgBuf[pos], "radio=1", sizeof("radio=1")-1)) {
          LEDR_Off();
        }
      }
      res = SendWebPage(ch_id, LEDR_Get()!=FALSE, 20/*dummy temperature*/, io);
      if(res!=ERR_OK && io!=NULL) {
        CLS1_SendStr("Sending page failed!\r\n", io->stdErr); /* copy on console */
      }
    }

Finally, it closes the connection at the end:

1.CLS1_SendStr("INFO: Closing connection...\r\n", io->stdOut);

2. res = ESP_CloseConnection(ch_id, io, ESP_DEFAULT_TIMEOUT_MS);

With this, I handle GET and POST messages and can toggle the LED on my board :-) :-).

Summary

It is amazing what is possible with this tiny and inexpensive ($4.50) WiFi module. The simple AT interface allows small and tiny microprocesors to connect to the internet or the local network. With all the hype around ‘Internet of Things’ this is where things very likely will end up: small nodes connecting in an easy way to the network. The processor on that ESP8266 is probably more powerful than the KL25Z (the specs and data sheets of that ESP8266 are still evolving). Or it is possible to run that module in standalone mode too which is a very interesting approach too, see the links at the end of this article. But still having an UART way to connect to the network is very useful and powerful. Other modules costs multiple times more. I expect that many vendors will come up with similar integrated modules e.g. to combine an ARM processor with the WiFi radio, similar that ESP8266 module. For sure that ESP8266 has a head start and paved the way how WiFi connectivity should work. We all will see what the future brings. Until then, that ESP8266 module is something I can use in many projects :-).

The sources and project files can be found on GitHub:
https://github.com/ErichStyger/mcuoneclipse/tree/master/Examples/KDS/FRDM-KL25Z/FRDM-KL25Z_ESP8266

Happy Web-Serving :-)

Useful Links:

Web server Command (computing) Connection (dance) shell Interface (computing) Data (computing) LEd application Command-line interface

Published at DZone with permission of Erich Styger, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

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Tutorial: Web Server with the ESP8266 WiFi Module

Outline

Board Connections

Communication Protocol

Project Creation

Sources

Processor Expert Components

Sending Commands

Using the Shell

Connection Test

Module Restart

Access Point or Device

List of Access Points

Connecting to Access Point

IP Address

Building a Web Server

Number of Connections: CIPMUX

Starting the Server: CIPSERVER

Connecting to the Server with Browser

Sending Data to Server: CIPSEND

Closing Connection: CIPCLOSE

Web Server Implementation

Summary

Useful Links:

Related

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