scheduling - Round robin worst case response time -

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the pseudo-codes below shows typical round robin software architecture. if every device requires 20ms service , updatelcd() requires 10ms execute, worst case response time?

void main (void) {    while(1) {      if (!! device needs service) {           !! handle device      }       if (!! device b needs service) {          !! handle device b      }       . . . .       if (!! device d needs service) {          !! handle device d      }       updatelcd();    } }

since there total of 4 devices (a,b,c,d) , if after servicing device a, device needs servicing, worst case response time here should 20+20+20+10 = 70ms (assuming devices b, c , d needs servicing).

however, in answer selection, there only: 85ms, 110ms, 35ms , 25ms. think need on understanding of round robin architecture.. thanks!

first, math wrong: if there 4 devices (a, b, c, , d), worst case time 20*4 + 10 = 90ms.

by process of elimination, though, can't 85, 35, or 25 (since provided times multiples of 10), "correct" answer must 110… assume 5 devices, not four.


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