pit.h

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/* Copyright (c) 2010 Wildfire Games
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/*
 * Timer implementation using 82C53/4 PIT
 */

#ifndef INCLUDED_PIT
#define INCLUDED_PIT

// note: we don't access the PIT for two reasons:
// - it rolls over every 55 ms (1.193 MHz, 16 bit) and would have to be
//   read at least that often, which would require setting high thread
//   priority (dangerous).
// - reading it is slow and cannot be done by two independent users
//   (the second being QPC) since the counter value must be latched.
//
// there are enough other counters anway.

static const i64 PIT_FREQ = 1193182;    // (= master oscillator frequency/12)

#endif  // #ifndef INCLUDED_PIT