clear Keyboard Buffer \ VOGONS

clear Keyboard Buffer

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First post, by thrawn235

Posted on 2020-04-08, 15:06

thrawn235 Offline

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Posts: 32
Joined: 2019-03-25, 16:42

I use DJGPP and ive installed a Keyboard ISR.
everything works fine.
The only Problem is, that when i quit the Program, all the Keypresses that i did (during program execution) show up on the Dos promt.

Is there a way to clear the Buffer at the End of the Game or not have it record keypresses in the first place ?
Or rather, what is the usual way of doing that ?

thanks.

Reply 1 of 3, by Ringding

Posted on 2020-04-08, 19:10

Ringding Offline

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There is a ring buffer somewhere in the BIOS area, whose head and tail positions can be set. I forgot the details. But how does your application handle keyboard input? Does it handle int 9 itself? If it does it on its own, then there should be no need to call the original int 9 handler, thus nothing would end up in the keyboard buffer.

Reply 2 of 3, by thrawn235

Posted on 2020-04-08, 20:30

thrawn235 Offline

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Joined: 2019-03-25, 16:42

Thats basically what im doing:

1
2//============= global Variables for the Interrupt Service Routine ========
3bool keys[256];
4//=========================================================================
5
6//============ global Function that is to be installed as ISR =============
7void KeyboardInterruptRoutine()
8{
9	unsigned char scanCode = 0;
10	scanCode = inportb( 0x60 );
11	if( scanCode != 0 )
12	{
13		if( scanCode <= 80 && scanCode )
14		{
15			keys[scanCode] = true;
16		}
17		else
18		{
19			keys[scanCode - 0x80] = false;
20		}
21		if( scanCode == 0xe0 )
22		{
23			unsigned char scanCode2 = 0;
24			scanCode2 = inportb( 0x60 );
25			if( scanCode2 <= 80 )
26			{
27				keys[scanCode2+100] = true;
28			}
29			else
30			{
31				keys[scanCode2+100 - 0x80] = false;
32			}
33		}
34	}
35
36	char temp;
37	outportb( 0x61, ( temp = inportb( 0x61 )) | 0x80 );
38	outportb( 0x61, temp );
39}
40//unused dummy functions. meant to calculate the size of KeyboardInterruptRoutine()
41void KeyboardInterruptRoutineEnd() {} 
42//======================================================================
43
44void DOSInputEngine::InstallKeyboardInterrupt()
45{
46	_go32_dpmi_lock_data( ( void* )keys, ( long )sizeof( keys ) );
47	_go32_dpmi_lock_code( ( void* )KeyboardInterruptRoutine, 1000 );
48 	_go32_dpmi_get_protected_mode_interrupt_vector( 0x09, &OldISR );
49	
50	NewISR.pm_offset = ( int )KeyboardInterruptRoutine;
51	NewISR.pm_selector = _go32_my_cs();
52
53	_go32_dpmi_chain_protected_mode_interrupt_vector( 0x09, &NewISR );
54}

After thinking about it, the Problem is probably that i chain the the interrupt.

Does anybody know how to just overwrite it ?

Reply 3 of 3, by ripsaw8080

Posted on 2020-04-08, 20:49

ripsaw8080 Offline

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Posts: 5087
Joined: 2006-04-25, 23:24

I guess you just need to change "chain" to "set" in the function name. Of course your handler may need to be different if it doesn't chain, e.g. acknowledging the keyboard IRQ.

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