A projects/04/fill/Fill-unrolled.asm

@@ -0,0 +1,115 @@ 
+// 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.
+
+// Fill: for length of screen, checks keypress. If keypress is nonzero, set
+// R2 to -1 (black), otherwise set R2 to 0 (white). Do 8 times: set two 16-bit
+// words in screen to R2 ("coloring white or black").
+
+// Point to next 16
+// pixels and repeat to enf of screen, then restart at start of screen.
+// 
+// R0 - current screen pointer (to-be incremented until end of screen is hit)
+// R1 - DRAW_SCREEN_LOOP local loop counter (for optimized drawing of 2 rows)
+// R2 - 0 or -1 (white or black), stored 16-pixel pattern to draw
+
+// zero initialize local variables
+@R1
+M=0
+@R2
+M=0
+
+(SET_SCREEN_PTR)
+    // R0 = SCREEN pointer
+    @SCREEN
+    D=A
+    @R0
+    M=D
+
+(IS_KEYPRESSED)
+    // end of screen: 0x5fff (dec 24575)
+    // if R0 >= (24575 - 8); goto SET_SCREEN_PTR
+    @R0
+    D=M
+    @24567
+    D=D-A
+    @SET_SCREEN_PTR
+    D;JGE
+
+    // D=KBD, goto WHITE_SCREEN if D == 0
+    @KBD
+    D=M
+    @WHITE_SCREEN
+    D;JEQ
+
+(BLACK_SCREEN)
+    @R2
+    M=-1
+    @DRAW_SCREEN_LOOP
+    0;JMP
+
+(WHITE_SCREEN)
+    @R2
+    M=0
+
+(DRAW_SCREEN_LOOP)
+    // D = <16-bit pixel pattern to draw>
+    @R2
+    D=M
+    // *R0++ = -1; *R0++ = -1 (unrolled and optimized)
+    @R0
+    A=M
+    M=D
+    A=A+1
+    M=D
+    D=A+1
+    @R0
+    M=D
+
+      // *R0++ = -1 (unrolled and unoptimized, old)
+    //@R0
+    //A=M
+    //M=D
+    //@R0
+    //M=M+1
+      // *R0++ = -1
+    //@R0
+    //A=M
+    //M=D
+    //@R0
+    //M=M+1
+
+    // increment local loop counter
+    @R1
+    M=M+1
+    
+    // if (R1 - 8) > 0, then exit local loop, otherwise loop back
+    @R1
+    D=M
+    @7
+    D=D-A
+    @DRAW_SCREEN_LOOP
+    D;JLE
+
+    // set local loop count to zero, return to test if key is pressed
+    @R1
+    M=0
+    @IS_KEYPRESSED
+    0;JMP
+
+// should never reach here, but just in case...
+(END)
+    @END
+    0;JMP
+

M projects/04/fill/Fill.asm → projects/04/fill/Fill.asm

@@ -13,9 +13,11 @@ // the screen should remain fully clear as long as no key is pressed.
 
 // Put your code here.
 
-// TODO: optimize better in the future
-
-// have separate branch _only_ for drawing black/white pixels
+// Fill: for length of screen, checks keypress. If keypress is nonzero, set
+// current 16 pixels to black, otherwise set them to white. Point to next 16
+// pixels and repeat to enf of screen, then restart at start of screen.
+//
+// R0 - current screen pointer (to-be incremented until end of screen is hit)
 
 (SET_SCREEN_PTR)
     // R0 = SCREEN pointer
@@ -24,10 +26,8 @@ D=A
     @R0
     M=D
 
-// TODO: fix infinitely incrementing screen pointer bug
-// end of screen: 0x5fff (dec 24575)
-
 (IS_KEYPRESSED)
+    // end of screen: 0x5fff (dec 24575)
     // if R0 == 24575; goto SET_SCREEN_PTR
     @R0
     D=M