Slowing down a program (in c and assembly) using interrupts

Question

I want to slow down a program using interrupts according to these conditions :

• if I press the up arrrow on the keyboard the speed will increase
• if I press the down arrow on the keyboard the speed will decrease

I want to do it by using interrupts : if the speed should decrease I will mask more interrupts and if the speed should increase I will unmask interrupts.
I know how to reach to the keyboard interrupt and to mask and unmask interrupts.
I just don't know how to reach the program speed. I am writing the code in c and assembly.

Answer 1

One thing you can do is to intercept one of the interrupts such as the BIOS clock tick int 08h or (better) MS-DOS int 1Ch handler called at about 18 hertz. Then add time-wasting loops based on a variable that is controlled by certain keyboard events.

Make sure you re-enable interrupts before each delay.

At the end of the program you are responsible for restoring the original interrupt vector.

You can't speed a program up faster than its starting speed without adjusting the emulation.