Embedded Systems Design, 2nd Edition

140 Embedded systems design

These devices can also provide a system tick signal for use by the

operating system.

Simulating a real-time clock in software

These can be simulated in software by programming a

timer to generate a periodic event and simply using this as a

reference and counting the ticks. The clock functions are then

created as part of the software. When enough ticks have been

received it updates the seconds counter and so on. There are two

problems with this: the first concerns the need to reset the clock

when the system is turned off and the second concerns the accu-

racy which can be quite bad. This approach does save on a special

clock chip ...