what is the instruction of cortex-M0 for divide calculation

The Cortex-M0 processor does not have a hardware divider, which means that division calculations are performed using software routines. There are various algorithms for performing software division, but one commonly used method is called "long division".

In long division, the divisor is repeatedly subtracted from the dividend until the remainder is less than the divisor. The number of times the divisor is subtracted is the quotient, and the remainder is the final result. This process is repeated until all digits of the dividend have been processed.

Here is a sample code for performing integer division on Cortex-M0 using long division:

int divide(int dividend, int divisor)
{
   int quotient = 0, remainder = 0;
   int sign = ((dividend < 0) ^ (divisor < 0)) ? -1 : 1;

   // convert both operands to positive
   if (dividend < 0) dividend = -dividend;
   if (divisor < 0) divisor = -divisor;

   // perform long division
   for (int i = 31; i >= 0; i--)
   {
      remainder <<= 1;   // left shift remainder
      remainder |= (dividend >> i) & 1;  // add next bit from dividend to remainder

      if (remainder >= divisor)
      {
         remainder -= divisor;
         quotient |= (1 << i);  // set corresponding bit in quotient
      }
   }

   // apply sign
   quotient = sign * quotient;

   return quotient;
}

Note that this code assumes that both the dividend and divisor are 32-bit integers. It also handles negative operands correctly and applies the correct sign to the result. However, it may not be the most efficient implementation and may need to be optimized for specific use cases.