pit.h File Reference

#include <stdint.h>

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Functions
void	pit_configure_channel (int channel, int mode, int frequency)
	devices/pit.h More...

Function Documentation

pit_configure_channel()

void pit_configure_channel	(	int	channel,
		int	mode,
		int	frequency
	)

devices/pit.h

devices/pit.h

In a PC, the PIT's three output channels are hooked up like this:

• Channel 0 is connected to interrupt line 0, so that it can be used as a periodic timer interrupt, as implemented in Pintos in devices/timer.c.
• Channel 1 is used for dynamic RAM refresh (in older PCs). No good can come of messing with this.
• Channel 2 is connected to the PC speaker, so that it can be used to play a tone, as implemented in Pintos in devices/speaker.c.

MODE specifies the form of output:

• Mode 2 is a periodic pulse: the channel's output is 1 for most of the period, but drops to 0 briefly toward the end of the period. This is useful for hooking up to an interrupt controller to generate a periodic interrupt.
• Mode 3 is a square wave: for the first half of the period it is 1, for the second half it is 0. This is useful for generating a tone on a speaker.
• Other modes are less useful.

FREQUENCY is the number of periods per second, in Hz.

Definition at line 46 of file pit.c.

References ASSERT, intr_disable(), intr_set_level(), mode, outb(), PIT_HZ, PIT_PORT_CONTROL, and PIT_PORT_COUNTER.

Referenced by speaker_on(), and timer_init().

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