computer science

$6.$ For the following code, show all work to calculate the number of instruction cycles required to execute the following code, including the time to call this function with BL sumU$32$ and the time to return from the function with BXLR$.$ You can assume that the pipeline is full before the BL sumU$32$ instruction is executed. When calling the function, assume that the count $\backslash (=3\backslash ).$

Assume that most instructions take $1$ clock, unconditional branches $($B$,$ BX$,$ LR$)$ take $2$ clocks, and conditional branches take $3$ clocks if the branch is taken and $1$ if the branch is not taken. Also assume that LDR takes $2$ clocks.

$```$

$//$ wint$32\_$t sumU$32($const uint$32\_$t x$|$l$,$ uint$32\_$t count$)$

$//$ address of x$[0]$ in RO$,$ count in R$1,$ return sum in R$0$

sumJ$]32$:

MOV R$2,$ R$0$

MOV RO$,$ $$0$

sumU$32\_1$oop:

CMP R$1,$ $$0$

BEQ sumU$32\_$end

LDR R$3,[$R$2],$ #$4$

ADD RO$,$ R$0,$ R$3$

SUB R$1,$ R$1,$ #$1$

B sum$032\_$loop

sumU$32\_$end:

BX LR

$```$

Clock cycles

If the clock rate is $4$ GHz $,$ what is the execution time in nanoseconds?