Add disassembled delay timer from Matthew Mikolay

asm/Makefile

@@ -4,7 +4,8 @@ ASM_FLAGS=
 all: rocket.rom	\
 	 jumping_X_and_O.rom \
 	 Fishie.rom \
-	 random_number_test.rom
+	 random_number_test.rom \
+	 delay_timer_test.rom 
 
 rocket.rom: rocket.asm chip8.asm
 	customasm -o $@ $(ASM_FLAGS) $<
@@ -21,6 +22,10 @@ mytest.rom: mytest.asm chip8.asm
 random_number_test.rom: random_number_test.asm chip8.asm
 	customasm -o $@ $(ASM_FLAGS) $<
 
+delay_timer_test.rom: delay_timer_test.asm chip8.asm
+	customasm -o $@ $(ASM_FLAGS) $<
+
+
 .phony: clean
 clean:
 	rm *.rom

asm/delay_timer_test.asm

@@ -0,0 +1,39 @@
+#include "chip8.asm"
+
+main:
+    LD V6, 1            ; Set y := 1
+.a:
+    CALL draw           ; Draw value in V3
+    LD V4, K            ; Wait for key-press
+    SNE V4, 2           ; Skip if not K != 2 (up)
+    ADD V3, 1           ; V3 := V3 + 1, if K == 2, increase timer
+    SNE V4, 8           ; Skip it not K != 8 (down)
+    SUB V3, V6          ; V3 := V3 - V6 (1)
+    SE V4, 5            ; Skip if K == 5
+    JP .a               ; Cycle and wait for new input
+    LD DT, V3           ; K == 5, set delay timer to selected value
+.b:
+    LD V3, DT           ; Load delay timer in to V3
+    CALL draw           ; Draw
+    SE V3, 0            ; Skip if V3 (delay-timer) equals zero
+    JP .b               ; Loop back to b (until DT reaches zero)
+    JP .a               ; Loop back to a
+
+; Draw the value stored in V3 at the location V5, V6
+;   The registers V0, V1, V2 are used as workspace
+draw:
+    CLS                 ; Clear the screen
+    LD V5, 0            ; Set x := 0
+    LD I, end           ; Point I to free memory past the end of the program
+    LD B, V3            ; Load binary-decimal for V3
+    LD V2, [I]          ; Load registers V(0:2) = memory(I:I+2)
+    LD F, V0            ; Load sprite for 1st character
+    DRW V5, V6, 5       ; Draw character
+    LD F, V1            ; Load sprite for 2nd character
+    LD V5, 5            ; Set x := 5
+    DRW V5, V6, 5       ; Draw character
+    LD F, V2            ; Load sprite for 3rd character
+    LD V5, 10           ; Set x := 10
+    DRW V5, V6, 5       ; Draw character
+    RET                 ; Return
+end:                    ; Label to empty area past the end of the program