78 lines
2.2 KiB
C
78 lines
2.2 KiB
C
#include <stdint.h>
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#include <stdbool.h>
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#include <sys/cpu.h>
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#if defined(UEFI)
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#include <efi.h>
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#include <lib/misc.h>
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#endif
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uint64_t tsc_freq = 0;
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void calibrate_tsc(void) {
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tsc_freq = tsc_freq_arch();
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if (tsc_freq != 0) {
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return;
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}
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#if defined(UEFI)
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// Calibrate over 10ms. Run multiple rounds and take the smallest
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// (least SMI-disrupted) delta.
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#define EFI_CALIBRATION_STALL 10000
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#define EFI_CALIBRATION_ROUNDS 3
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uint64_t best_delta = 0;
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for (int round = 0; round < EFI_CALIBRATION_ROUNDS; round++) {
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uint64_t tsc_start = rdtsc();
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gBS->Stall(EFI_CALIBRATION_STALL);
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uint64_t tsc_end = rdtsc();
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if (tsc_end > tsc_start) {
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uint64_t delta = tsc_end - tsc_start;
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if (delta < best_delta || best_delta == 0) {
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best_delta = delta;
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}
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}
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}
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if (best_delta != 0) {
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tsc_freq = best_delta * (1000000ULL / EFI_CALIBRATION_STALL);
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}
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#elif defined(BIOS)
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// Calibrate TSC using PIT channel 2.
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// PIT oscillator frequency: 1193182 Hz
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// Count of 11932 gives ~10ms calibration interval.
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// Run multiple rounds and take the smallest (least SMI-disrupted) result.
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#define PIT_CALIBRATION_COUNT 11932
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#define PIT_CALIBRATION_ROUNDS 3
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uint8_t port61 = inb(0x61);
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uint64_t best_delta = 0;
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for (int round = 0; round < PIT_CALIBRATION_ROUNDS; round++) {
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outb(0x61, port61 & ~0x03); // disable gate and speaker
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outb(0x43, 0xb0); // channel 2, lobyte/hibyte, mode 0, binary
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outb(0x42, PIT_CALIBRATION_COUNT & 0xff);
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outb(0x42, (PIT_CALIBRATION_COUNT >> 8) & 0xff);
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outb(0x61, (inb(0x61) | 0x01)); // enable gate to start counting
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uint64_t tsc_start = rdtsc();
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while ((inb(0x61) & 0x20) == 0); // wait for output high
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uint64_t tsc_end = rdtsc();
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if (tsc_end > tsc_start) {
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uint64_t delta = tsc_end - tsc_start;
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if (delta < best_delta || best_delta == 0) {
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best_delta = delta;
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}
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}
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}
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outb(0x61, port61); // restore
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if (best_delta != 0) {
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tsc_freq = best_delta * 1193182 / PIT_CALIBRATION_COUNT;
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}
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#endif
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}
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