Friday, May 31, 2013

From Nand to Tetris - Project 4 (Fill)

This is my solution to the exercises (Fill) in Project 4 of the free course From Nand to Tetris
Other Links:
http://www.cs.huji.ac.il/course/2002/nand2tet/projects.html
// 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. When no key is pressed, the
// program clears the screen, i.e. writes "white" in every pixel.

// (RESET_SCREEN_COUNTER)
 // @SCREEN
 // D=A
 // @counter
 // M=D    // counter = SCREEN

(LISTEN_FOR_NO_KEY_PRESS)
 // reset screen counter
 @SCREEN
 D=A
 @counter
 M=D
 
 // if KBD == 0 jump to CLEAR_SCREEN
 @KBD
 D=M
 @CLEAR_SCREEN
 D;JEQ

 // loop (keep on checking if KBD == 0
 @LISTEN_FOR_NO_KEY_PRESS
 0;JEQ

(LISTEN_FOR_KEY_PRESS)
 // reset screen counter
 @SCREEN
 D=A
 @counter
 M=D
 
 // if KBD > 0 jump to BLACKEN_SCREEN
 @KBD
 D=M
 @BLACKEN_SCREEN
 D;JGT
 
 // loop (keep on checking if KBD > 0
 @LISTEN_FOR_KEY_PRESS
 0;JEQ
 
(BLACKEN_SCREEN) 
 // blacken 16-bit memory location
 @counter
 A=M    // A = counter
 M=-1   // blacken current memory location
  
 // if KBD == 0 jump to LISTEN_FOR_NO_KEY_PRESS (to reset counter)
 @KBD
 D=M
 @LISTEN_FOR_NO_KEY_PRESS
 D;JEQ

 // increment counter
 @counter
 M=M+1
 
 // check if you have reached memory location 24575 (the final address for the screen)
 D=M
 @24575
 D=A-D
 @LISTEN_FOR_NO_KEY_PRESS
 D;JLT   // goto LISTEN_FOR_NO_KEY_PRESS if counter > 24575
 
 // loop BLACKEN_SCREEN if you have NOT reached memory location 24575
 @BLACKEN_SCREEN
 0;JEQ 

(CLEAR_SCREEN)
 // clear 16-bit memory location
 @counter
 A=M    // A = counter
 M=0    // clear current memory location
 
 // if KBD > 0 jump to LISTEN_FOR_KEY_PRESS (to reset counter)
 @KBD
 D=M
 @LISTEN_FOR_KEY_PRESS
 D;JGT
 
 // increment counter
 @counter
 M=M+1
 
 // check if you have reached memory location 24575 (the final address for the screen)
 D=M
 @24575
 D=A-D
 @LISTEN_FOR_KEY_PRESS
 D;JLT   // goto LISTEN_FOR_KEY_PRESS if counter > 24575
 
 // loop CLEAR_SCREEN if you have NOT reached memory location 24575
 @CLEAR_SCREEN
 0;JEQ