Check contents of buffer after serial read

Question

I would like to test the contents of data received over a serial connection. In my loop() I store the data in bffr; and afterwards I would like to test to see if there are some predefined words in it.

#define BFFSZ 90
char bffr[BFFSZ];
char bffridx; 
void loop()
{
 readline();
 //- Test the bffr
 if(strstr(bffr, "CLOSED")){ //- WORKS
 Serial.println("> conn. closed");
 digitalWrite(A1, HIGH); 
 }else if(strstr(bffr, "RING")){ //- WORKS
 Serial.println("> Someone is ringing");
 digitalWrite(A2, HIGH);
 }else if(strstr(bffr, "0,7,j,BLINK")){ //- Doesn't work
 Serial.println("> Blink");
 digitalWrite(A2, HIGH);
 delay(300);
 digitalWrite(A2, LOW);
 }
}
void readline()
{
 memset(bffr,0,sizeof(bffr));
 char c;
 int i =0;
 bffridx = 0; // start at beginning
 long previousMillis = millis();
 while (1) {
 unsigned long currentMillis = millis();
 if(currentMillis - previousMillis > 20000) {
 Serial.println("TIMEOUT");
 return;
 }
 delay(2);
 c=gsm.SimpleRead2();
 //- debug only, to see if there is something received. 
 Serial.write(c);
 if (c == -1)
 continue;
 if (c == '\n')
 continue;
 if ((bffridx == BFFSZ-1) || (c == '\r')) {
 bffr[bffridx] = 0;
 return;
 }
 bffr[bffridx++]= c;
 delay(2);
 }
}

The debug-line makes that I can see the data flowing, eg when I phone the SIM.

But it looks like the buffer isn't tested properly. The first two will work, but the last test fails. It is part of a larger string: 0,7,ドルj,BLINK,567^ But I thought the strstr(1,2) searches for 2 in 1. And as 0,7,j,BLINK, is within the haystack I assume it wil return true. But apparently not...

The gsm.SimpleRead2() comes from GSMlib and is my altered version of gsm.SimpleRead(). Instead of printing the char, I just return it so we can buffer it in the readline function.

void SIMCOM900::SimpleRead()
{
 char datain;
 if(_cell.available()>0){
 datain=_cell.read();
 if(datain>0){
 Serial.print(datain);
 }
 }
}
char SIMCOM900::SimpleRead2()
{
 char datain;
 if(_cell.available()>0){
 datain=_cell.read();
 if(datain>0){
 return datain;
 }
 }
}

Does anyone know the answer to this?

• jfpoilpret: Did you check that gsm.SimpleRead2() never returns non-printable characters (ASCII 0x00-0x1F)? That could explain why you don't see anything in the debug with Serial and the searched string can then not be found.
• jfpoilpret: By the way, where does this GSM library SimpleRead2 come from? Could you provide a link?
• stUrb: @jfpoilpret I've added the simpleread functions and a link to the library.
• stUrb: So there might be some strange characters in the bffr which causes the test to fail. How can I strip a string with non-printable characters?
• jfpoilpret: If there are strange characters in the GSM output, then it is quite easy to check and skip: you can use isPrintable(c) to check it and add c to bffr only in that case. This is part of standard C library, there are many other isXxxx(c) functions defined in WCharacter.h.

Answer 1

After a serial.read();, the data [as far as I can tell] is pretty much destroyed. You have two main options to accomplish this:

• Store the data in a string when read and then reference this later. I'd do this with a global variable, that is declared outside of a method and accessible throughout your whole sketch.
• I haven't read throughout your whole code, but, if you only need to read one character, you can use serial.peek();. This only works if you need the first character of the buffer.

Most likely, your only option would be the first bullet. I'd implement this by adding a method something like this:

String buffer_string_serial;
void setup() { //code here }
void loop() { //code here }
int serial_read_buffer() {
 while(serial.avaliable() > 0) {
 buffer_string_serial = buffer_string_serial + serial.peek();
 return serial.read();
 }
}

Then, just use serial_read_buffer();. That will act similar to serial.read();. The only difference is it will fill up the buffer_string_serial string. You'll have to clear that out after you used all the data so it doesn't get full.

• stUrb: That's what I've done with the readline() It stores everything in a global bffr. And afterwards I try to test it; but the testing doesn't work.
• Anonymous Penguin: @stUrb Test it with expressions? I'd recommend verifying the string is exactly what you want and revisiting your testing code. Maybe print the string before testing to the serial window?
• stUrb: Checking for an exact match is not easy. The protocol consists of an unique integer at the end, describing a job id: 0,7,ドルj,JOB,ID^ so everything except the ID is know and can be tested. Does Arduino/C has some kind of regular expression test/match?
• Anonymous Penguin: @stUrb I can't find built in support in the Arduino core libraries for regex, but this library here for Arduino (with pretty good documentation) might help you.