CSCI 461 Lab 3
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(a) Port preemptive-RIOS to the m68hc11.  

(b) RIOS is clock-driven in the sense that it uses the gcd of task periods
to determine when a scheduling event occurs.  For example, let the task
set be T1 = (2, 0.1), T2 = (3, 0.1), T3 = (6, 0.1).  The gcd(2, 3, 6)
is 1. Consequently, RIOS executes its scheduler (via an ISR) every 1
time unit. The actual scheduling events occur at times 0, 2, 3, 4, 6, ...
Modify RIOS such that it is event-driven (scheduler is invoked only when
there is a scheduling event).

Deliverables
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Demonstration of your port to the m68hc11.
A printout of your code (both C and Assembly).

With regard to scheduler invocation, you must be able to highlight the
difference between clock-driven and event-driven scheduling.