// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/04/Fill.asm

// Runs an infinite loop that listens to the keyboard input.
// When a key is pressed (any key), the program blackens the screen,
// i.e. writes "black" in every pixel;
// the screen should remain fully black as long as the key is pressed. 
// When no key is pressed, the program clears the screen, i.e. writes
// "white" in every pixel;
// the screen should remain fully clear as long as no key is pressed.

// Put your code here.

// addr = SCREEN map start address
@SCREEN
D=A
@addr
M=D

// reg = SCREEN map register total count
@8192
D=A
@reg
M=D

// itr = current register count
@itr
M=0

// black if pix = -1
// white if pix = 0
@pix
M=-1

// loop declaration
// D = reg - itr
// if 0 jump to @END
// else continue
    (LOOP)
@itr
D=M
@reg
D=D-M
@END
D;JEQ

// addr = 16384..24575
// @16384 = pix
// @16385 = pix
// .
// .
// @24575 = pix
@pix
D=M
@addr
A=M
M=D

// itr = itr + 1
// addr = addr + 1
@itr
M=M+1
@addr
M=M+1

//back to loop declaration
@LOOP
0;JMP


// clear the screen if no key pressed:
// pix = 0
// itr = 0
// addr = 16384
// back to loop declaration
    (CLEAR)
@pix
M=0

@itr
M=0

@SCREEN
D=A
@addr
M=D

@LOOP
0;JMP

// paint the screen if no key pressed:
// pix = -1
// itr = 0
// addr = 16384
// back to loop declaration
    (PAINT)
@pix
M=-1

@itr
M=0

@SCREEN
D=A
@addr
M=D

@LOOP
0;JMP

// main feedback loop
// jump to @CLEAR if no key pressed
// jump to @PAINT if any key pressed
    (END)
@KBD
D=M
@CLEAR
D;JEQ

@KBD
D=M
@PAINT
D;JGT

@END
0;JMP