diff options
Diffstat (limited to 'src/northbridge')
| -rw-r--r-- | src/northbridge/intel/i945/udelay.c | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/src/northbridge/intel/i945/udelay.c b/src/northbridge/intel/i945/udelay.c index 9170335bd5..ce5e9d8943 100644 --- a/src/northbridge/intel/i945/udelay.c +++ b/src/northbridge/intel/i945/udelay.c @@ -2,6 +2,7 @@ * This file is part of the coreboot project. * * Copyright (C) 2007-2008 coresystems GmbH + * 2012 secunet Security Networks AG * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by @@ -22,6 +23,17 @@ #include <cpu/x86/tsc.h> #include <cpu/x86/msr.h> +/* Simple 32- to 64-bit multiplication. Uses 16-bit words to avoid overflow. */ +static inline void multiply_to_tsc(tsc_t *const tsc, const u32 a, const u32 b) +{ + tsc->lo = (a & 0xffff) * (b & 0xffff); + tsc->hi = ((tsc->lo >> 16) + + ((a & 0xffff) * (b >> 16)) + + ((b & 0xffff) * (a >> 16))); + tsc->lo = ((tsc->hi & 0xffff) << 16) | (tsc->lo & 0xffff); + tsc->hi = ((a >> 16) * (b >> 16)) + (tsc->hi >> 16); +} + /** * Intel Core(tm) cpus always run the TSC at the maximum possible CPU clock */ @@ -33,7 +45,6 @@ void udelay(u32 us) msr_t msr; u32 fsb = 0, divisor; u32 d; /* ticks per us */ - u32 dn = 0x1000000 / 2; /* how many us before we need to use hi */ msr = rdmsr(0xcd); switch (msr.lo & 0x07) { @@ -63,10 +74,9 @@ void udelay(u32 us) msr = rdmsr(0x198); divisor = (msr.hi >> 8) & 0x1f; - d = fsb * divisor; + d = (fsb * divisor) / 4; /* CPU clock is always a quarter. */ - tscd.hi = us / dn; - tscd.lo = (us - tscd.hi * dn) * d; + multiply_to_tsc(&tscd, us, d); tsc1 = rdtsc(); dword = tsc1.lo + tscd.lo; |