In assembly language, design and implement an interrupt based keyboard
input system.

This should include a buffer large enough to hold a long line of input.
The characters should be efficiently packed, four in each 32 bit word.

The IV$KEYBD interrupt must be enabled and trapped. When it is received,
the $TERMINC PERI command should be used to receive the newly typed
characters and they should be transferred to the buffer.

This system must properly process at least:
  + the backspace key
  + correctly echoing user input
  + control-U to erase the whole current line

For user program access, you must provide the following functions:
  getchar_nw()  [nw = no wait]
     If a whole \n-terminated line is available in the buffer,
     remove and return the first character. If a line is not
     available, immediately return -1.
  getchar()
     Wait until a whole line is avaiable in the buffer, then
     (using getchar_nw) return one character
  backchar(c)
     Reverses the effect of c = getchar(). Puts a character back
     at the front of the buffer so it may be re-read later.
  getint()
     Uses getchar() to read a whole decimal integer and return
     its value as a 32 bit word.

Make a good test that clearly demonstrates your implementation working.

submit code and screen-shots.