在 android 工作室中将 4 个 integer 字节组合为 32 位无符号整数

Question

I want to send a 32bit timestamp from my stm32wb55 to my own android app. This is how I split the timestamp in 4 bytes on the microcontroller and send these over BLE to my phone:

void calculate_timestamp(void){

//splitting in 4 bytes
uint8_t time_micro32_1 = time_micro32 & 0xFF;
uint8_t time_micro32_2 = (time_micro32 >> 8) & 0xFF;
uint8_t time_micro32_3 = (time_micro32 >> 16) & 0xFF;
uint8_t time_micro32_4 = (time_micro32 >> 24) & 0xFF;

//send the bytes over ble
P2P_Server_App_Context.Acceleration.Timestamp_1 = time_micro32_1; //8
P2P_Server_App_Context.Acceleration.Timestamp_2 = time_micro32_2; //9
P2P_Server_App_Context.Acceleration.Timestamp_3 = time_micro32_3; //10
P2P_Server_App_Context.Acceleration.Timestamp_4 = time_micro32_4; //11

}

"time_micro32" includes the time in microseconds since startup from the microcontroller and will be displayed correct on my putty-console: And this is how I combine the 4 bytes in android studio:

//NotificationValue[8] includes value of time_micro32_1
//NotificationValue[9] includes value of time_micro32_2
//NotificationValue[10] includes value of time_micro32_3
//NotificationValue[11] includes value of time_micro32_4

int Timestamp = (NotificationValue[8] << 24) | (NotificationValue[9] << 16) | (NotificationValue[10] << 8) | (NotificationValue[11]);

I display the timestamp in my activity like this:

  ((TextView) findViewById(R.id.Time_TextView)).setText("Timestamp = "+ Timestamp );

But the values in my activity never makes sense. The values are false and be often negativ (what is never desired by timestamps).

I think, I combine the bytes in android studio not the right way. But I have no more idea how can I do this. I tried many, but nothing was successfull.

Does anyone have an idea how can I combine the bytes in android correctly? Or have I made a mistake by splitting the timestamp on my microcontroller? In the end, I want to display the timestamp in microseconds on my activity as a 32bit unsigned integer.

Thankfull about every help...

---

EDIT: At the end, I have noticed that I have interchanged my MSB and LSB in my timestamp, too. This would be the right order:

    int Timestamp = (NotificationValue[11] << 24) | (NotificationValue[10] << 16) | (NotificationValue[9] << 8) | (NotificationValue[8]);

Answer 1

it's not a one liner but you can try this to get the bytes re-assembled.

    unsigned int timestamp = NotificationValue[8];

timestamp = (timestamp<<8)+NotificationValue[9];
timestamp = (timestamp<<8)+NotificationValue[10];
timestamp= (timestamp<<8)+NotificationValue[11];

for some reason i feel that the bit shifts you were doing was mangling the data.

edit:

didn't know java doesn't use unsigned types. You could use a long instead, and convert it to unsigned.

long timestamp = NotificationValue[8];

timestamp= (timestamp<<8) + NotificationValue[9];
timestamp= (timestamp<<8)+ NotificationValue[10];
timestamp = (timestamp<<8)+ NotificationValue[11];

timestamp = timestamp & 0xffffffffL; //this should remove the signage

Answer 2

unsigned integer

byte[] NotificationValue = new byte[] { (byte)0xFC, (byte)0xFD, (byte)0xFE, (byte)0xFF };
long Timestamp =
      ((NotificationValue[0] & 0xFFL) << 24) //00000000_00000000_00000000_00000000_11111111_00000000_00000000_00000000
    | ((NotificationValue[1] & 0xFFL) << 16) //00000000_00000000_00000000_00000000_00000000_11111111_00000000_00000000
    | ((NotificationValue[2] & 0xFFL) <<   8) //00000000_00000000_00000000_00000000_00000000_00000000_11111111_00000000
    |  (NotificationValue[3] & 0xFFL); //00000000_00000000_00000000_00000000_00000000_00000000_00000000_11111111

signed integer

byte[] NotificationValue = new byte[] { (byte)0xFC, (byte)0xFD, (byte)0xFE, (byte)0xFF };
int Timestamp =
       (NotificationValue[0] << 24) //11111111_00000000_00000000_00000000
    | ((NotificationValue[1] & 0xFF) << 16) //00000000_11111111_00000000_00000000
    | ((NotificationValue[2] & 0xFF) <<  8)  //00000000_00000000_11111111_00000000
    |  (NotificationValue[3] & 0xFF);       //00000000_00000000_00000000_11111111