Atlas - SDL_systimer.c
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[FILE BEGIN]
1/*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2026 Sam Lantinga <[email protected]>
4
5  This software is provided 'as-is', without any express or implied
6  warranty.  In no event will the authors be held liable for any damages
7  arising from the use of this software.
8
9  Permission is granted to anyone to use this software for any purpose,
10  including commercial applications, and to alter it and redistribute it
11  freely, subject to the following restrictions:
12
13  1. The origin of this software must not be misrepresented; you must not
14     claim that you wrote the original software. If you use this software
15     in a product, an acknowledgment in the product documentation would be
16     appreciated but is not required.
17  2. Altered source versions must be plainly marked as such, and must not be
18     misrepresented as being the original software.
19  3. This notice may not be removed or altered from any source distribution.
20*/
21#include "SDL_internal.h"
22
23#ifdef SDL_TIMER_DOS
24
25#include <dos.h>  /* delay */
26#include <time.h> /* uclock, uclock_t, UCLOCKS_PER_SEC */
27
28#include "../../core/dos/SDL_dos_scheduler.h"
29
30/* DJGPP's uclock() reprograms PIT channel 0 for a higher tick rate on first
31   call, giving ~1.19 MHz resolution (UCLOCKS_PER_SEC == 1193180).  This is
32   the same approach SDL2-dos used and gives sub-microsecond precision without
33   any extra setup. */
34
35Uint64 SDL_GetPerformanceCounter(void)
36{
37    return (Uint64)uclock();
38}
39
40Uint64 SDL_GetPerformanceFrequency(void)
41{
42    return (Uint64)UCLOCKS_PER_SEC;
43}
44
45void SDL_SYS_DelayNS(Uint64 ns)
46{
47    if (ns == 0) {
48        DOS_Yield();
49        return;
50    }
51
52    const uclock_t delay_start = uclock();
53    const uclock_t target_ticks = (uclock_t)((ns * UCLOCKS_PER_SEC) / SDL_NS_PER_SECOND);
54
55    while ((uclock() - delay_start) < target_ticks) {
56        /* Always yield first so cooperative threads can run. */
57        DOS_Yield();
58
59        /* If more than 1 ms remains, do a short sleep to avoid burning
60           100% CPU when no other threads need to run.  DJGPP's delay()
61           is a busy-wait but it does halt-loop on the PIT, which is
62           lighter than a tight uclock() poll. */
63        uclock_t remaining = target_ticks - (uclock() - delay_start);
64        if (remaining > (UCLOCKS_PER_SEC / 1000)) {
65            delay(1);
66        }
67    }
68}
69
70#endif /* SDL_TIMER_DOS */
71
[FILE END]
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