| 1 | #include <stdint.h> |
| 2 | #include <stdbool.h> |
| 3 | #include <sys/cpu.h> |
| 4 | #if defined(UEFI) |
| 5 | #include <efi.h> |
| 6 | #include <lib/misc.h> |
| 7 | #endif |
| 8 | |
| 9 | uint64_t tsc_freq = 0; |
| 10 | |
| 11 | void calibrate_tsc(void) { |
| 12 | tsc_freq = tsc_freq_arch(); |
| 13 | if (tsc_freq != 0) { |
| 14 | return; |
| 15 | } |
| 16 | |
| 17 | #if defined(UEFI) |
| 18 | // Calibrate over 10ms. Run multiple rounds and take the smallest |
| 19 | // (least SMI-disrupted) delta. |
| 20 | #define EFI_CALIBRATION_STALL 10000 |
| 21 | #define EFI_CALIBRATION_ROUNDS 3 |
| 22 | |
| 23 | uint64_t best_delta = 0; |
| 24 | for (int round = 0; round < EFI_CALIBRATION_ROUNDS; round++) { |
| 25 | uint64_t tsc_start = rdtsc(); |
| 26 | gBS->Stall(EFI_CALIBRATION_STALL); |
| 27 | uint64_t tsc_end = rdtsc(); |
| 28 | |
| 29 | if (tsc_end > tsc_start) { |
| 30 | uint64_t delta = tsc_end - tsc_start; |
| 31 | if (delta < best_delta || best_delta == 0) { |
| 32 | best_delta = delta; |
| 33 | } |
| 34 | } |
| 35 | } |
| 36 | |
| 37 | if (best_delta != 0) { |
| 38 | tsc_freq = best_delta * (1000000ULL / EFI_CALIBRATION_STALL); |
| 39 | } |
| 40 | #elif defined(BIOS) |
| 41 | // Calibrate TSC using PIT channel 2. |
| 42 | // PIT oscillator frequency: 1193182 Hz |
| 43 | // Count of 11932 gives ~10ms calibration interval. |
| 44 | // Run multiple rounds and take the smallest (least SMI-disrupted) result. |
| 45 | #define PIT_CALIBRATION_COUNT 11932 |
| 46 | #define PIT_CALIBRATION_ROUNDS 3 |
| 47 | |
| 48 | uint8_t port61 = inb(0x61); |
| 49 | |
| 50 | uint64_t best_delta = 0; |
| 51 | for (int round = 0; round < PIT_CALIBRATION_ROUNDS; round++) { |
| 52 | outb(0x61, port61 & ~0x03); // disable gate and speaker |
| 53 | outb(0x43, 0xb0); // channel 2, lobyte/hibyte, mode 0, binary |
| 54 | outb(0x42, PIT_CALIBRATION_COUNT & 0xff); |
| 55 | outb(0x42, (PIT_CALIBRATION_COUNT >> 8) & 0xff); |
| 56 | |
| 57 | outb(0x61, (inb(0x61) | 0x01)); // enable gate to start counting |
| 58 | uint64_t tsc_start = rdtsc(); |
| 59 | |
| 60 | while ((inb(0x61) & 0x20) == 0); // wait for output high |
| 61 | uint64_t tsc_end = rdtsc(); |
| 62 | |
| 63 | if (tsc_end > tsc_start) { |
| 64 | uint64_t delta = tsc_end - tsc_start; |
| 65 | if (delta < best_delta || best_delta == 0) { |
| 66 | best_delta = delta; |
| 67 | } |
| 68 | } |
| 69 | } |
| 70 | |
| 71 | outb(0x61, port61); // restore |
| 72 | |
| 73 | if (best_delta != 0) { |
| 74 | tsc_freq = best_delta * 1193182 / PIT_CALIBRATION_COUNT; |
| 75 | } |
| 76 | #endif |
| 77 | } |
