gps_data gps_get_time(void) {
printf("Getting time...");
gps_data data = gps_init_data();
u8 msg[28];
gps_request(gps_time_request);
gps_read_message(msg, 28);
printf("done.\r\n");
if(gps_bad_header(msg))
return data;
if(gps_bad_id(msg, 0x21))
return data;
if(gps_bad_checksum(msg, 28))
return data;
u8 valid = msg[6+19];
if(!valid & 0x01)
// This checks for valid time of week, ignoring week number
// and UTC (don't care if a few seconds out because we don't know
// the current GPS-UTC offset, and don't care if we don't know the date
// since we do not use it).
return data;
data.hour = msg[6+16];
data.minute = msg[6+17];
data.second = msg[6+18];
data.data_valid = 1;
return data;
}
gps_data gps_get_position(void) {
printf("Getting position...");
gps_data data = gps_init_data();
u8 msg[36];
gps_request(gps_position_request);
gps_read_message(msg, 36);
printf("done.\r\n");
if(gps_bad_header(msg))
return data;
if(gps_bad_id(msg, 0x02))
return data;
if(gps_bad_checksum(msg, 36))
return data;
s32 lon = (msg[10] | msg[11] << 8 | msg[12] << 16 | msg[13] << 24);
s32 lat = (msg[14] | msg[15] << 8 | msg[16] << 16 | msg[17] << 24);
s32 alt = (msg[22] | msg[23] << 8 | msg[24] << 16 | msg[25] << 24);
data.latitude = (double)lat / (double)1E7;
data.longitude = (double)lon / (double)1E7;
data.altitude = alt / 1E3;
if(data.latitude > 90.0 || data.latitude < -90.0)
return data;
if(data.longitude > 180.0 || data.longitude < -180.0)
return data;
data.data_valid = 1;
return data;
}
gps_data gps_get_status(void) {
printf("Getting status...");
gps_data data = gps_init_data();
u8 msg[24];
gps_request(gps_status_request);
gps_read_message(msg, 24);
printf("done.\r\n");
if(gps_bad_header(msg))
return data;
if(gps_bad_id(msg, 0x03))
return data;
if(gps_bad_checksum(msg, 24))
return data;
u8 gpsFix = msg[6+4];
u8 flags = msg[6+5];
if((gpsFix == 0x02 || gpsFix == 0x03 || gpsFix == 0x04) && (flags & 1))
data.lock_valid = 1;
else
data.lock_valid = 0;
data.data_valid = 1;
return data;
}
int main(int argc, char **argv)
{
char msg[MAX_GPS_MSG_LEN+1];
struct bcm2835_i2cbb ibb;
uint32_t speed = 250;
uint32_t kbit = 100;
if (argc > 1) {
kbit = atoi(argv[1]);
switch (kbit) {
case 50: speed = 500; break; // 500 gives roughly 50Kbit/s
case 100: speed = 250; break; // 250 gives roughly 100Kbit/s
case 200: speed = 100; break; // 100 gives roughly 200Kbit/s
case 300: speed = 50; break; // 50 gives roughly 300Kbit/s
case 400: speed = 23; break; // 23 gives roughly 400Kbit/s
default:
printf("Bad speed '%s'=%u, should be 50,100,200,300 or 400\n", argv[1], kbit);
exit(1);
}
}
printf("Using speed ~ %u Kbit/s\n", kbit);
// address, sda,scl,clock_freq,timeout
if(bcm2835_i2cbb_open(&ibb,0x42,2,3,speed,1000000)) {
printf("Failed to initialize bitbanged I2C. Aborting...\n");
exit(1);
}
while(1) {
int len = gps_read_message(&ibb, msg);
if (len > 0) {
gps_process_message(msg, len);
}
gps_delay_ms(100);
}
exit(0);
}
