Add changeable FPS

README.md

@@ -34,6 +34,12 @@ Emulation speed
 ---------------
 Instructions are run 500 times a second
 
+Issues
+------
+* Player sprites tend to flicker. (See e.g. BRIX) Why? Also, this seems to
+  happen in the haxe-chip-8-emulator too, and lowering the FPS doesn't seem
+  to help, which suggests something fishy with the programs
+
 Requirements
 ------------
 * pyglet (`pip3 install pyglet`)

sipsi-8.py

@@ -40,10 +40,11 @@ def key_released(symbol):
 			break
 
 def draw_screen():
+	global display_screen
 	to_draw = []
 	for y in range(32):
 		for x in range(64):
-			if screen[y * 64 + x]:
+			if display_screen[y * 64 + x]:
 				to_draw.append((x, y))
 
 	screen_points = []
@@ -223,10 +224,24 @@ def step():
 
 	# Dxyn draw vx, vy, n
 	elif high_byte >> 4 == 0xD:
-		# TODO: OSCOM Nano manual (page 38) says "<The screen
-		# behaves as if the top was connected to the bottom and
-		# the sides to each other.>" Investigate how this wrapping
-		# should be implemented
+		# OSCOM Nano manual (page 38) says "<The screen behaves as
+		# if the top was connected to the bottom and the sides to
+		# each other>", but I can't find any info on how to do this
+		# wrapping on the generally used sources.
+		#
+		# https://github.com/AfBu/haxe-chip-8-emulator looks like
+		# it wraps the pixels to the next row down, but as it
+		# doesn't seem to handle drawing out the bottom of the
+		# screen at all, unsure how intentional this is.
+		#
+		# https://github.com/dmatlack/chip8 wraps the pixels on the
+		# other side of the same line.
+		#
+		# The game "Blitz" seems to require draws off the bottom of
+		# the screen to not result in anything. Therefore, as I
+		# have yet to find any games that break with it, I'm just
+		# skipping pixels that fall outside the screen.
+
 		x_start = data_registers[high_byte & 0xf]
 		y_start = data_registers[low_byte >> 4]
 
@@ -239,14 +254,12 @@ def step():
 			y = y_start + dy
 			# Screen is 32 lines tall
 			if y >= 32:
-				# TODO: Figure how y >= 32 works
 				continue
 
 			for dx in range(8):
 				x = x_start + dx
 				# Screen is 64 columns wide
 				if x >= 64:
-					# TODO: Figure how x >= 64 works
 					continue
 
 				# Pixels are stored MSB-left
@@ -368,16 +381,26 @@ def tick_timers():
 		sound_timer = 0
 
 def advance_interpreter(dt):
-	global cpu_speed
-	global cpu_cycles_to_go
-	# Each tic (60Hz) we need to run cpu_clock / 60Hz cycles
+	global cpu_clock
+	global screen, display_screen, screen_fps
+	global cpu_cycles_to_go, frames_to_go
+	# Each tic (60Hz) we need to run cpu_clock / 60Hz cycles and
+	# draw screen_fps / 60 frames
 	cpu_cycles_to_go += cpu_clock / 60
+	frames_to_go += screen_fps / 60
 	tick_timers()
 	
 	while cpu_cycles_to_go >= 1:
 		step()
 		cpu_cycles_to_go -= 1
 
+	if frames_to_go >= 1:
+		# Only draw the latest frame. This means FPS >60 won't work
+		# but why would you ever want to run chip-8 faster than
+		# that
+		display_screen = screen[:]
+		frames_to_go -= int(frames_to_go)
+
 def initialize_ram():
 	global ram, font_start
 	ram = [0]*(1<<12)
@@ -613,8 +636,11 @@ def initialize_ram():
 	#ram[0x200:len(test_program) + 0x200] = test_program
 
 def initialize_screen():
-	global screen
+	global screen, display_screen, screen_fps
 	screen = [False] * 64 * 32
+	display_screen = screen[:]
+	# TODO: Support changing FPS
+	screen_fps = 60
 
 def initialize_timers():
 	global delay_timer, sound_timer
@@ -654,10 +680,14 @@ def load_program(f):
 
 def main():
 	global window
-	global cpu_cycles_to_go
-	# Don't hardcode the size
+	global cpu_cycles_to_go, frames_to_go
+	# TODO: Don't hardcode the size
 	window = pyglet.window.Window(640, 320, resizable = True)
 
+	# Don't use pulse driver, as it is really buggy and can crash the
+	# python process
+	pyglet.options['audio'] = ('openal', 'directsound', 'silent')
+
 	# Hook up our screen drawing routine
 	@window.event
 	def on_draw():
@@ -680,10 +710,12 @@ def main():
 	initialize_keyboard()
 	initialize_cpu()
 
+	# TODO: Deal with missing file gracefully
 	with open(sys.argv[1], 'rb') as f:
 		load_program(f)
 
 	cpu_cycles_to_go = 0
+	frames_to_go = 0
 	# Start the emulation
 	pyglet.clock.schedule_interval(advance_interpreter, 1/60)