please answer using Cortex - M4 instruction

Write a recursive assembly subroutine that calculates the sum of K integers that are ordered in decreasing value from K to 1, that is, sum = K + (K 1) + (K-2) + ... +3+2+1. As an example, if K = 5, then sum = 5+4 + +3+2 +1. Assume that K is passed to assembly subroutine using register r0 and that sum returned via ro