problems about mpu 6050

It tries to connect the slave to the master, pair and transmit the pitch, roll, and yaw values through Bluetooth. However, the transmitted value is all constant at 90, and I don't know what the problem is. The pitch roll yaw value of mpu 6050 comes out well, and simply sending and receiving values without using mpu 6050 goes well.

//slave
#include <SoftwareSerial.h>

SoftwareSerial btSerial(3,2);

void setup() {
  btSerial.begin(9600);
  Serial.begin(9600);
}

void loop() {
  if(btSerial.available()){
    Serial.print("  roll   ");
    long a = btSerial.parseInt();
    Serial.print(a);
    Serial.print("  pitch   ");
    long b = btSerial.parseInt();
    Serial.print(b);
    Serial.print("  yaw   ");
    long c = btSerial.parseInt();
    Serial.print(c);    
    Serial.println("");
}
}
//master
#include <Wire.h>
#include <MPU6050.h>
#include <SoftwareSerial.h>
MPU6050 mpu;

SoftwareSerial btSerial(3,2);
// Timers
unsigned long timer = 0;
float timeStep = 0.01;

// Pitch, Roll and Yaw values
float pitch = 0;
float roll = 0;
float yaw = 0;

void setup() 
{
  btSerial.begin(9600);
  Serial.begin(9600);
  // Initialize MPU6050
  while(!mpu.begin(MPU6050_SCALE_2000DPS, MPU6050_RANGE_2G))
  {
    Serial.println("Could not find a valid MPU6050 sensor, check wiring!");
    delay(500);
  }
  
  // Calibrate gyroscope. The calibration must be at rest.
  // If you don't want calibrate, comment this line.
  mpu.calibrateGyro();

  // Set threshold sensivty. Default 3.
  // If you don't want use threshold, comment this line or set 0.
  mpu.setThreshold(3);
}

void loop()
{
  timer = millis();

  // Read normalized values
  Vector norm = mpu.readNormalizeGyro();

  // Calculate Pitch, Roll and Yaw
  pitch = pitch + norm.YAxis * timeStep;
  roll = roll + norm.XAxis * timeStep;
  yaw = yaw + norm.ZAxis * timeStep;

  int pitchmap= map(pitch ,-100,100,0,180);
  int rollmap = map(roll,-100,100,0,180);
  int yawmap = map(yaw, -100,100,0, 180);
  Serial.print(pitchmap);
  Serial.print(rollmap);  
  Serial.println(yawmap);
  // Wait to full timeStep period
  btSerial.println(pitchmap);
  btSerial.println(rollmap);
  btSerial.println(yawmap);
  delay(10);
 
}

one basic principle in programming is doing one thing at a time.
This means

1.) write a testcode that maps values from pre-defined constants print the input-value and the output-value of the mapping-function to the local serial port.

2.) if this does work integrate the readings from your MPU-sensors

alternative insert debug-outut at all intesting lines of code to see where do you get which value

best regards Stefan