heintze@grane.enet.dec.com (Siegfried Heintze) (08/30/90)
I'm using MSDOS software interrupt 0x33, function 0x0c to establish a routine (called ime) to be called by the mouse driver everytime the mouse changes state (ie, (ie, everytime a button is depressed or released or the position of the mouse changes.) This works because I can call the zortech routine "sound_click()" to verify that it is working. I remember reading somewhere that it is necessary to call interrupt 0x33 function 2 before writing to the VGA to prevent a conflict. This function hides the mouse pointer on the VGA to prevent the mouse driver and you from trying to access VGA simultaneously. This is an important consideration because writing to the VGA is not an atomic operation. It consists of writing to multiple VGA registers via I/O ports. Interrupting this sequence with another write sequence would not be desireable. So we tell the mouse driver not update the mouse pointer on the VGA while we are accessing the VGA display RAM and when we are done we use INT 0x33 func 1 to display the mouse pointer again. I tried just writing to the VGA display from the routine called by INT 0x33 func 0x0c and it did not hang. But when I tried to write a character to the VGA display using a call to MSDOS (INT 0x10 function 9) it hangs. No surprise, I probably needed to hide the mouse. I have discovered that if I concentrate on not moving the mouse and very slowly depressing and releasing the mouse button, I can update the VGA with out hanging. So I call int 0x33 func 2 to hide the mouse inside my function ime that is called by the mouse driver. This hangs my machine. Why? How do I diagnose this problem further? Sieg