Page 411 - Programming Microcontrollers in C

396 Chapter 8 MCORE, A RISC Machine

#include “mmc2001.h”
#include “timer.h”

/***************************************************
Delay by t milliseconds. The data here are passed
as an int because, this routing ties up the
computer the whole delay time. An alternate means
should be used if a long delay is needed. This
routine uses the PIT which counts at about 122 us
per ticks. It is not very accurate because, the
count is at 1/8192 seconds, more nearly 122.070312
us ticks. Not good enough to make a clock, but
good enough to control a few milliseconds.

This modification assumes that the pit is enabled
and shall remain enabled. TVS 6/2000
****************************************************/
void delay(WORD t)
{
UWORD now,next;
UWORD count;

count=(long)t*1000; /* make the delay in us */
count/=122; /* 122 us per tick */
ITCSR.EN=ON; /* enable the pit */
while(count>0) /* there are probably faster ways to do */
{ /* this, but who cares, you are killing time */
now = ITADR; /* and don’t care for speed */
do
{
next = ITADR;
} while(now==next); /* wait until next tick */
count—–;
}
ITCSR.EN=OFF; /* delay is done don’t need the pit now */
}
Listing 8-1: Delay routine
The function parameter time is the delay time in milliseconds.
The clocking rate for the counter is each 122.0… microseconds.
Therefore the time is converted to counts when it is divided by 122.
The PIT is then enabled with the instruction

ITCSR.EN = ON; /* enable the pit */