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Make CLK_INTERVAL depend on HZ; update comments to match.

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scottr 1996-04-01 05:16:52 +00:00
parent 5f20924433
commit bbb6251b0b
1 changed files with 11 additions and 6 deletions
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17
sys/arch/mac68k/mac68k/clockreg.h
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@ -1,4 +1,4 @@
/* $NetBSD: clockreg.h,v 1.4 1996/02/01 03:40:26 briggs Exp $ */
/* $NetBSD: clockreg.h,v 1.5 1996/04/01 05:16:52 scottr Exp $ */
/*-
* Copyright (C) 1993 Allen K. Briggs, Chris P. Caputo,
@ -40,19 +40,24 @@
#define CLK_SPEED 0.0000012766 /* time to complete a clock (3 MHz) */
#define CLK_INTERVAL 13055 /* clks to hit HZ ticks/sec */
/*
* The VIA1 clock speed is 1.2766us, so the timer value above is:
* Calculate clocks needed to hit HZ ticks/sec.
*
* The VIA clock speed is 1.2766us, so the timer value needed is:
*
* 1 1,000,000us 1
* CLK_INTERVAL = -------- * ----------- * ------
* 1.2766us 1s HZ
*
* where HZ == 60. This gives us 13055.5 and change... We round down.
* While it may be tempting to simplify the following further, we can run
* into integer overflow problems. Also note: do *not* define HZ to be
* less than 12; overflow will occur, yielding invalid results.
*/
#define CLK_INTH (CLK_INTERVAL >> 8)
#define CLK_INTL (CLK_INTERVAL & 0xff)
#define CLK_INTERVAL ((int)((((100000000L / HZ) * 100) / 12766)))
#define CLK_INTH ((CLK_INTERVAL >> 8) & 0xff) /* high byte */
#define CLK_INTL (CLK_INTERVAL & 0xff) /* low byte */
#if !defined(PRF_INTERVAL)
#define PRF_INTERVAL CLK_INTERVAL