Hidden function in Pinguino

I am working with a GSM modem and Pinguino. To send command to the modem, i used the UART and AT commands. The problem was to set a correct time out when receiving answer from the modem. I wanted to use the millis instruction, but i was afraid by an overflow of the time variable.
So i decided to use a hidden variable in Pinguino, _millis. This variable is used in the arduinodelay library and is incremented every milli second. I copied this example of my code:

 #include <string.h>

unsigned char caractere;
unsigned char chaine[50];
long tempo;
unsigned char index;

unsigned char gsm_echo(unsigned char state)
{
Serial.flush();
_millis=0;
index=0;
if (state) Serial.print("ATE1\r");
 else Serial.print("ATE0\r");
while (_millis<100)
 {
 if Serial.available()
   {
   caractere=Serial.read();
   chaine[index]=caractere;
   index++;
   }
 }
chaine[index]=0;
if (strstr(chaine,"OK")!=0) return 0;
else return 1;
}

void setup()
{
Serial.begin(9600);
pinMode(0,OUTPUT);
digitalWrite(0,LOW);
tempo=millis();
}

void loop() 
{ 
debut: 
delay(500); 
if (gsm_echo(0)==1) goto debut; 
delay(500); 
digitalWrite(0,HIGH); 
while (1);
}

The millis instruction in the setup function is just used to initialise the library.
_millis variable is already declared in the arduinodelay library.

Hope it will be useful for everybody.