GPS receive on pin B2, how to timeout (PIC16F876)

[runtime]

Hello all,

PIC16f876

I am receiving GPS readings on pin B2, I did not used any software or hardware interrupts to read the GPS because I wanted to poll the GPS instead of jumping to an interrupt routine every time a GPS char is present.

So, everytime I need a GPS position, I call a routine to get the characters using fgetc(GPS), this works ok if the GPS is connected but hangs up when GPS is disconnected, how can I timeout when GPS is disconnected?

Thank you in advance
Peter

[dyeatman]

Have you tried polling using kbhit() before calling fgetc()?

[Humberto]

[runtime]

// Nmea is pin B2
// GetPosition function reads $GPRMS sentence and buffers only relevant info, I need a way to get out of GetPosition if GPS not present...

#use rs232(baud=4800,rcv=Nmea,invert,stream=GPS)
#use rs232(baud=4800,xmit=MOut,rcv=MIn,stream=MODEM)
#use rs232(baud=4800,xmit=PCOut,invert,stream=PC) // RS232 to PC

// --------------------
// Function GetPosition // Parse $GPRMC
// --------------------
void GetPosition(void)
{

start: while (v != 'G') v=fgetc(GPS); // Finds the GPRMC sentence
v = fgetc(GPS);
if (v != 'P') goto start;
v = fgetc(GPS);
if (v != 'R') goto start;
v = fgetc(GPS);
if (v != 'M') goto start;
v = fgetc(GPS);
if (v != 'C') goto start;

fpoint = False; // first point found?
comma = 0; // Count comma chars
status = 0; // Build status bit

i = 0; // Buffer the GPRMC sentence
do {
v = fgetc(GPS);

if (v == ',') comma++;
if (comma == 6) v = '*'; // final marker

if ((v == '.') && (!fpoint)) { // discard .999 in time field
fpoint = True;
v = fgetc(GPS);
v = fgetc(GPS);
v = fgetc(GPS);
v = fgetc(GPS);
}
if (v == 'A'){ // Check for svs
sat = True;
if (firstpos) {
firstpos = False;
seconds = StoreInt - 1;
}
output_high(Valid);
bit_set(status,2);
v = fgetc(GPS); // Discard A,
v = fgetc(GPS);
}
else if (v == 'V') {
sat = False;
if (!input(Valid))(output_high(Valid)); // Flash Valid GPS led if not valid
else (output_low(Valid));
v = fgetc(GPS); // Discard V,
v = fgetc(GPS);
}
if (v == 'S') bit_set(status,3); // Build status bit
if (v == 'E') bit_set(status,4);

if ((v == 'N') || (v == 'S') || (v == 'W') || (v == 'E')) { // Discard N,S,W,E,
v = fgetc(GPS);
v = fgetc(GPS);
}

buf[i] = v; // Fill buffer
i++;
if (i == (MAXBUF - 2)) break;
} while (v != '*');

if (!input(Panic)) { // Check panic btn condition
remote = True;
if (!GPRSStarted && !LineOpen) BaseCall = True;
}

if (!input(Door)) { // Check Doors
DoorS = True;
if (!GPRSStarted && !LineOpen && !AckDoor) BaseCall = True;
}
else AckDoor = False;

if (remote) bit_set(status,0); // Panic bit
if (DoorS) bit_set(status,5); // Door sensor

if (!read_eeprom(12)) bit_set(status,1); // Engine Off bit

if (bit_test(status,0) && (!logP)) { // Log Panic On
seconds = StoreInt - 1;
logP = True;
ZeroStore = False;
}
if (!bit_test(status,0) && (logP)) { // Log Panic Off
seconds = StoreInt - 1;
logP = False;
ZeroStore = False;
}

if (bit_test(status,5) && (!logD)) { // Log Door Open
seconds = StoreInt - 1;
logD = True;
ZeroStore = False;
}
if (!bit_test(status,5) && (logP)) { // Log Door Close
seconds = StoreInt - 1;
logD = False;
ZeroStore = False;
}

status = status + 33;

zip(); // Compress buffer

}

[dyeatman]

A much better (cleaner) approach would be something like this: