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dos: Drain BIOS keyboard buffer in event pump to prevent overflow beeps

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palxex
2026-06-27 16:42:42 +08:00
committed by Ryan C. Gordon
parent 46dcc0c554
commit ac6e7c795e
1 changed files with 19 additions and 12 deletions
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31
src/video/dos/SDL_dosevents.c
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@@ -252,6 +252,20 @@ static Uint8 keyevents_ringbuffer[256];
static int keyevents_head = 0;
static int keyevents_tail = 0;
static void DOSVESA_DrainBIOSKeyboardBuffer(void)
{
__dpmi_regs regs;
for (;;) {
regs.h.ah = 0x01; // BIOS: check for keystroke
__dpmi_int(0x16, &regs);
if (regs.x.flags & 0x40) { // ZF set = buffer empty
break;
}
regs.h.ah = 0x00; // BIOS: read keystroke (removes it)
__dpmi_int(0x16, &regs);
}
}
void DOSVESA_PumpEvents(SDL_VideoDevice *device)
{
/* Give cooperative threads a chance to run. Audio mixing now runs
@@ -322,6 +336,10 @@ void DOSVESA_PumpEvents(SDL_VideoDevice *device)
}
}
// We chain IRQ1 to BIOS, so drain its keyboard queue continuously to prevent
// BIOS buffer overflow beeps during long key autorepeat.
DOSVESA_DrainBIOSKeyboardBuffer();
SDL_Mouse *mouse = SDL_GetMouse();
if (mouse->internal) { // if non-NULL, there's a mouse detected on the system.
__dpmi_regs regs;
@@ -380,18 +398,7 @@ void DOSVESA_QuitKeyboard(SDL_VideoDevice *device)
// Drain the BIOS keyboard buffer so held keys (like ESC) don't
// bleed through to the DOS command line after we exit.
{
__dpmi_regs regs;
for (;;) {
regs.h.ah = 0x01; // BIOS: check for keystroke
__dpmi_int(0x16, &regs);
if (regs.x.flags & 0x40) { // ZF set = buffer empty
break;
}
regs.h.ah = 0x00; // BIOS: read keystroke (removes it)
__dpmi_int(0x16, &regs);
}
}
DOSVESA_DrainBIOSKeyboardBuffer();
}
#endif // SDL_VIDEO_DRIVER_DOSVESA