Embedded Systems Design, 2nd Edition

Software examples 373

time slot. As a result, the time critical task may have to wait up to

a whole time slice period before it can start. In such worse cases,

this additional delay may be too long for the routine to complete

in response to the original demand or interrupt. If the triggers are

asynchronous, i.e. can happen at any time and are not particularly

tied to any one event, then the lack of pre-emption can cause a

wide range of timings. Unfortunately for real-time systems, it is

the worst case that has to be assumed and used in the design.

An alternative approach offered by some operating sys-

tems is the idea of an explicit lock where the task ...