GPS data blocked by other tasks in the while loop - gps

Question

I am trying to parse GPS data while reading pressure sensor, IMU sensor and writing some data to SD card. Since reading pressure sensor, IMU sensor and writing SD card takes some time and GPS don't wait my command to send its data, I lost some GPS data so my parser can not find meaningful message. I use uart_receive interrupt to take GPS data and circular buffer to save its data. After I parse it. Since I don't know how much bytes come from GPS, I read one by one. I tried FreeRTOS but it did not work. How can I prevent other tasks to block GPS data. I am using STM32f401cc.
Here is my FreeRTOS task;
void StartDefaultTask(void* argument)
{
IMU_setParameters(&imu, &hi2c1, imu_ADD_LOW, GPIOB, GPIOB,
GPIO_PIN_1, GPIO_PIN_2);
IMU_init(&imu, &htim3);
while ((calState.accel != 3 || calState.system != 3 || calState.gyro != 3 || calState.mag != 3) && calibFlg)
{
IMU_getCalibrationState(&imu, &calState);
}
preSensor_init_default_params(&preSensor.params);
preSensor.addr = preSensor_I2C_ADDRESS_1;
preSensor.i2c = &hi2c1;
preSensor_init(&preSensor, &preSensor.params);
initSD_CARD(&USERFatFS, USERPath);
samplePacket(&telemetry);
controlRecoveryFile(&recoveryFile, "recoveryFile.txt", &telemetry);
for (;;)
{
IMU_getDatas(&imu, &calState, &linearAccel, &IMU, &imuFlg, &offsetFlg, &calibCount);
preSensor_force_measurement(&preSensor);
preSensor_read_float(&preSensor, &temperature, &pressure, &humidty);
preSensor_get_height(pressure, &height);
telemetry.Altitude_PL = height;
telemetry.Pressure_PL = pressure;
telemetry.Temperature = temperature;
telemetry.YRP[0] = IMU.yaw;
telemetry.YRP[1] = IMU.roll;
telemetry.YRP[2] = IMU.pitch;
if (calibCount % 10 == 0)
{
writoToTelemetryDatas(&logFile, "tulparLog.txt", &telemetry, 0);
if (!writeToRecoveryDatas(&recoveryFile, "recoveryFile.txt", &telemetry))
connectionFlg = 1;
}
osDelay(1);
}
}
void StartTask02(void* argument)
{
arrangeCircularBuffer(&gpsCircular, buffer, BUFFER_LENGTH);
initGPS(&huart1, &rDATA, &gps);
for (;;)
{
getGPSdata(&huart1, &gpsCircular, &gps, &rDATA);
osDelay(1);
}
}

Answer 1

Here is my solution to problem.
First of all I do not use FreeRtos at all. I do all the thing in main loop. Problem is "Race Condition". In my GPS data parser, there are 4 states. MSG_ID, Finish, Check, Parse. These four states do not take four loops to find meaningfull message. It depends on message length. It can be at most 103 loop. Besides, In main loop my imu sensor, pressure sensor and SD card module takes approximately 80 ms. As you know, GPS works independent from our code. It does not wait our command to send data. Every 1 second it sends its datas. Now, imagine that your GPS sends datas every 1 seconds and your CircularBuffer has 200 bytes. Your parser begin to parse message. But your parser needs at least 30+ loops to find message. Now, 30*80 = 2400 ms (2.4 s). Untill you find meaningfull data GPS sent 2 more datas and overflow happened. To fix this situation, I write for loop for my GPS parser in the main loop and I send command to GPS for just taking GPGGA and GPRMC datas (for GPS command you can look at here. I use uart_receive_ınterrupt to store data to my circularbuffer. After taking 2 '\n', I stop taking data and wait my parser to parse these datas. At the end I start uart operation taking meaningfull datas. Important thing here is calling parser in a for loop. (it can be 8-16-24 loops depends on your other tasks delay)