Keyboard IRQ handler getting fired twice

[amittomar]

I followed the tutorial from http://www.osdever.net/bkerndev/index.php and wrote some code to handle IRQs.

I am having a peculiar issue. Whenever I press a key, the key I pressed gets printed correctly, but again the IRQ fires and a junk value gets printed as well. Can someone guide what direction should I be looking into ?

Can it be 'spurious interrupt', but then When I run the code taken from the same tutorial as it is, it works fine with no multiple prints.

P.S. I have implemented a Timer as well, and it works fine (fires once).

[xenos]

You know that you get interrupts both on key press and release?

http://www.win.tue.nl/~aeb/linux/kbd/sc ... html#ss1.1

[amittomar]

This is how I am handling the key press :

Code: Select all

// Handles the keyboard interrupt
void handleKeyPress(registerStructure *registerInformation)
{
   unsigned char keyPressed ;   
   unsigned short port = 0x60;
   
   // Read the value from data register
   asm volatile("inb %1, %0" : "=a" (keyPressed) : "dN" (port));

    // When a key is released, highest byte is set to 1
    if ( 1 == (keyPressed & 0x80))
    {
        // Handle shift/ctrl keys
    }
    
    // Key pressed
    else
    {        
	    putCharacterOnScreen(keyboardMapping[keyPressed]);	
    }
}

I think it takes appropriate care of both press and release ?

Now that you pointed towards it I noticed something in the output :

1. Valid key is printed as soon as I press the key
2. Invalid key is printed only when I release the key
3. If I keep the key pressed, it keep printing the valid key till I release, which is when an invalid key is printed once.

[jnc100]

If I was you compiler, I would have optimized

Code: Select all

    if ( 1 == (keyPressed & 0x80))
    {
        // Handle shift/ctrl keys
    }
    
    // Key pressed
    else
    {        
	    putCharacterOnScreen(keyboardMapping[keyPressed]);	
    }

to

Code: Select all

putCharacterOnScreen(keyboardMapping[keyPressed]);

Regards,
John.

[amittomar]

@XenOS

if ( 1 == (keyPressed & 0x80))

Here is the bug. It should just have been

if ( (keyPressed & 0x80))

Thanks a lot. You made me think in the right direction. Am new to the forums, anything I can do to give you 'reputation' in any sense ? Some way to 'vote you up' or anything ?

[amittomar]

Hehe seems I was just a minute late to realize and reply..

[xenos]

Thanks a lot. You made me think in the right direction. Am new to the forums, anything I can do to give you 'reputation' in any sense ? Some way to 'vote you up' or anything ?

I don't think that the forums have something like this, but reading that my advice could help you already makes my day