How to save SRAM

Projects Programming
1

Hi,
I am trying some example with ESP8266.Everything works well but I want save more SRAM and use PROGMEM function instead.
Can someone help how to do it with this piece of the code?

void serve_homepage(char ClientId) {
  String header  = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n";
  String content = "";
  content += "<p>WLAN Setup</p>";
  content += "<form method=GET>";
  content += "<label>SSID</label>
";
  content += "<input type='text'name='ssid'maxlength='30'size='15'>
";
  content += "<label>Password</label>
";
  content += "<input type='password'name='pass'maxlength='30'size='15'>

";
  content += "<input type='submit'value='CONNECT'>";
  content += "</form>";
  header  += "Content-Length:";
  header  += (int)(content.length());
  header  += "\r\n\r\n";

  Serial.print(F("AT+CIPSEND="));
  Serial.print(ClientId);
  Serial.print(",");
  Serial.println(header.length()+content.length());

  if(get_response("> ",2000)) {
    Serial.print(header);
    Serial.print(content);
  } 
  else {
    Serial.print(F("AT+CIPCLOSE="));
    Serial.println(ClientId);
  }
}

I tried this but it does not works - page is not loaded.

const char *const content PROGMEM  = 
"<form method=GET>"
"<label>SSID</label>
"
"<input type='text'name='ssid'maxlength='30'size='15'>
"
"<label>Password</label>
"
"<input type='password'name='pass'maxlength='30'size='15'>

"
"<input type='submit'value='CONNECT'>"
"</form>";
//--------------------
void serve_homepage(char ClientId) {
  String header  = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n";
  header  += "Content-Length:";
  header  += (int)strlen(content);
  header  += "\r\n\r\n";

  Serial.print(F("AT+CIPSEND="));
  Serial.print(ClientId);
  Serial.print(F(","));
  Serial.println(header.length()+strlen(content));

  if(get_response("> ",2000)) {
    Serial.print(header);
    Serial.print(*content);
  } 
  else {
    Serial.print(F("AT+CIPCLOSE="));
    Serial.println(ClientId);
  }
}

Can somebody help?
ppt

2

Hello and welcome,

Take a look at the progmem examples

3

Best advice is to rewrite your code without using the String Class and use char array's instead.

These can be easily stored in PROGMEM. - PROGMEM - Arduino Reference -

4

Hi Rob,
Can you please show on my code how to use char arrays?
I am beginner so I don't understand this technique so much...
It would be useful also for another users of this forum.
ppt

5

See also https://www.baldengineer.com/arduino-f-macro.html

6

Hi,
finally I got it working by this modification:

const  char string_0[] PROGMEM =  "<form method=GET>";
const  char string_1[] PROGMEM =  "<label>SSID</label>
";
const  char string_2[] PROGMEM =  "<input type='text'name='ssid'maxlength='30'size='15'>
";
const  char string_3[] PROGMEM =  "<label>Password</label>
";
const  char string_4[] PROGMEM =  "<input type='password'name='pass'maxlength='30'size='15'>

";
const  char string_5[] PROGMEM =  "<input type='submit'value='CONNECT'>";
const  char string_6[] PROGMEM =  "</form>";

const char* const content[] PROGMEM= {string_0 ,string_1 ,string_2 ,string_3 ,string_4 ,string_5 ,string_6 };
//*************************************************
void serve_homepage(char ClientId) {
  String header  = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n";
  header  += "Content-Length:";
  header  += 232;                  //  (sizeof(content)/sizeof(char *));
  header  += "\r\n\r\n";

  Serial.print(F("AT+CIPSEND="));
  Serial.print(ClientId);
  Serial.print(F(","));
  Serial.println(header.length()+232);  //Serial.println(header.length()+strlen(content));

  if(get_response("> ",2000)) {
    Serial.print(header);
    unsigned int count = 0;
    for (int i = 0; i < 7; i++){
      char * ptr = (char *) pgm_read_word (&content [i]);
      char buffer [500]; // must be large enough!
      strcpy_P (buffer, ptr);
      Serial.print (buffer);
      count += strlen (buffer) + 1;
    }  
  } 
  else {
    Serial.print(F("AT+CIPCLOSE="));
    Serial.println(ClientId);
  }
}

But another problem is how to calculate size of array 'content'.

for me works only this (gives 232):

Serial.println(strlen(content[0])+ strlen(content[1])+ strlen(content[2])+ strlen(content[3])+ strlen(content[4])+ strlen(content[5])+ strlen(content[6]));

but this one not works:(gives unrealistic numbers)

   for (int i = 0;i < 7;i++){
    cc = cc + strlen(content[i]);
    }
    Serial.println(cc);

can someone help why???my Arduino is latest 1.65.
thanks!

7

strlen_P ?

8

Hi,
can you more explain?
ppt

9

Here

10

The variable content[] is an array of pointers to your string arrays. Because each pointer requires 2 bytes and you have 7 of them, the size of content[] is 14, which I don't think is what you want. Also, you're mixing Strings (i.e., in header) with strings (content[]). (Note that Strings with a capital 'S' is not the same as strings with a lower case 's'.)

11

can you please write some example for me?
I didn't found anything what I can understand on the web.
ppt