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/*
* udelay() impementation for SMI handlers
* This is neat in that it never writes to hardware registers, and thus does not
* modify the state of the hardware while servicing SMIs.
*
* Copyright (C) 2014 Alexandru Gagniuc <mr.nuke.me@gmail.com>
* Subject to the GNU GPL v2, or (at your option) any later version.
*/
#include <cpu/x86/msr.h>
#include <cpu/x86/tsc.h>
#include <delay.h>
#include <stdint.h>
void udelay(uint32_t us)
{
uint8_t fid, did, pstate_idx;
uint64_t tsc_clock, tsc_start, tsc_now, tsc_wait_ticks;
msr_t msr;
const uint64_t tsc_base = 100000000;
/* Get initial timestamp before we do the math */
tsc_start = rdtscll();
/* Get the P-state. This determines which MSR to read */
msr = rdmsr(0xc0010063);
pstate_idx = msr.lo & 0x07;
/* Get FID and VID for current P-State */
msr = rdmsr(0xc0010064 + pstate_idx);
/* Extract the FID and VID values */
fid = msr.lo & 0x3f;
did = (msr.lo >> 6) & 0x7;
/* Calculate the CPU clock (from base freq of 100MHz) */
tsc_clock = tsc_base * (fid + 0x10) / (1 << did);
/* Now go on and wait */
tsc_wait_ticks = (tsc_clock / 1000000) * us;
do {
tsc_now = rdtscll();
} while (tsc_now - tsc_wait_ticks < tsc_start);
}
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