Why do you need scheduling ? Make a "work loop" call every task one after another and make all tasks - as a first - determine if they have anything to do and, if not, return immediately. If priority is required start the loop with the highest priority and make all tasks return to the top of the loop after processing if they went active. If time slicing/priority is it, have a loop counter this is an example adherence to assembly not attempted.

Counter = 0;
WorkLoop:
mov a,counter
cjne a,#8,NotReset
counter = 0
call prt 1
call prt 1
cjne counter,#2,NotTwo
call prt 2
call prt 2
NotTwo: cjne counter,#4,NotFour
call prt 2
call prt 2
call Prt3
call Prt3
NotFout: cjne counter,#6,WorkLoop
call prt 2
call prt 2
jmp WorkLoop

Erik