Keyboard Input System

Using only the system interrupt generated when a key on the keyboard is pressed, implement a simple but usable user-level input system.

You should implement at least a readint() function that could be used in this program (which of course you would have to code in assembly language):

        void main(void)
        { int x=readint();
          int y=readint();
          printf("%d + %d = %d\n", x, y, x+y); }

Being able to add two numbers together is not such a great thing, but being able to write a correctly functioning readint() demonstrates that you have got the input system working properly.

Characters received by the interrupt service routine that you write will have to be stored in a buffer somewhere, and user-level functions (like readint()) will have to be made to wait until there is a whole line in the buffer before they are allowed to take any characters from it.

Hint: first implement a readchar() function, whose job is to wait until there is a whole line in the buffer, then retrieve the first/next character from that buffer. Just like C's getchar(). All other user-level functions should make use of readchar() so they do not have to be concerned with the buffer or with waiting in any way.

You should also allow the user to currect simple mistakes by using the backspace or delete key. This is not difficult, and can cause a big improvement in the usability of a system.