MPD: lot of comments, fix blocking fifo read
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mpd_dot3k.py
91
mpd_dot3k.py
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@ -9,13 +9,27 @@ import threading
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import signal
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import sys
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import os
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import select
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import audioop
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import dot3k.lcd as lcd
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import dot3k.backlight as backlight
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import dot3k.joystick as nav
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from mpd import MPDClient
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rotate_pause = 10 # delay in rotation steps
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# When a line is too long to fit in a line of the LCD display,
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# it scrolls with a cool effect to let you read the entire text.
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# You may choose the speed of the scrolling and the pause between
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# two rotations.
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step_length = 0.2 # delay in seconds
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rotate_pause = 10 # delay in steps count
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# Symbols play, pause and stop are not defined in the dot3k library.
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# We need to draw them manually.
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# On the display, a character is a 8x5 pixels matrix. It is represented
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# in python as a list of 8 integers, one per line. Each integer has
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# 5 bits, one per raw.
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# It is easier to draw if you represent your integers in binary notation.
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char_play = [
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0b10000,
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@ -50,13 +64,46 @@ char_stop = [
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0b00000,
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]
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# We use a queue to communicate the song info to the display thread.
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# The main reason is that it has some amazing blocking properties that
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# enable not to think too much about mutex/lock/whatever logic you might
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# think about especially if you coded in C before.
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# It's python magic...
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q = queue.Queue()
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# This variable is the flag that will be turned down by the main thread
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# to notify the other threads that they need to stop in order for the
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# program to quit gracefully.
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run_event = threading.Event()
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def vumeter():
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'''
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This function will me used as the thread in charge of the LEDs
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behind the screen. We'll use them to watch the MPD output power
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in real time. Cool, huh? In order to do that, you need to configure
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an extra output in MPD by adding this snippet in /etc/mpd.conf:
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audio_output {
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type "fifo"
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name "my_fifo"
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path "/tmp/mpd.fifo"
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format "44100:16:2"
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}
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'''
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fifo = os.open('/tmp/mpd.fifo', os.O_RDONLY)
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while run_event.is_set():
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# When MPD is in pause or stopped, it doesn't write any EOF in the fifo
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# so os.read is blocked. In order to avoid that, we need to put a timeout,
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# and as os.open doesn't support any timeout, we need to put a select
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# before, as it has a timeout parameter. We only need the r return variable,
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# which is the list of readable file descriptors given in parameters,
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# returned as soon as one get ready or after the timeout.
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# We do all this in order to have a clean quit, else we wouldn't give a shit.
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r, w, e = select.select([ fifo ], [], [], 1)
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if fifo in r:
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try:
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# We read a chunk of the sound that MPD put in the FIFO.
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# Each chunk is a sequence of samples that describes the signal.
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rawStream = os.read(fifo, 4096)
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except OSError as err:
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if err.errno == errno.EAGAIN or err.errno == errno.EWOULDBLOCK:
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@ -64,19 +111,35 @@ def vumeter():
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else:
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raise
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if rawStream:
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# The RMS function calculates the square root of the average of
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# the squared samples: sqrt(sum(Si^2)/n)
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# This is a good power indicator.
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# Then, we just normalize it to reduce it between 0 and 1.
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# Finally, we call the set_graph methos that will display the
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# fraction by putting on the right number of LEDs.
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backlight.set_graph(audioop.rms(rawStream,2)/32768)
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# After exiting the almost-infinite loop, we turn the LEDs off.
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backlight.set_graph(0)
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def stringrotate(text, width, step):
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'''
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This function's purpose is to scroll the given text to the given step,
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knowing that the screen has the given width.
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'''
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if len(text) > width:
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fulltext = text + " - "
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fulltext = fulltext[step:] + fulltext[:step]
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return fulltext[:width]
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else:
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# No need to scroll the text if it can fit on the screen
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return text
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def display():
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'''
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This function will be run as the thread that will manage the LCD screan
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itself. It uses the global queue defined at the top of the script.
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'''
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title = ''
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artist = ''
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album = ''
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@ -84,7 +147,10 @@ def display():
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step_title = step_artist = step_album = 0
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while run_event.is_set():
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try:
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arg = q.get(timeout=0.2)
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# If a new MPD even comes before the timeout, grab it, else
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# throw an exception that will be caught.
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arg = q.get(timeout=step_length)
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# From here, we assume a new MPD event has occured (song or status change).
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status = arg['status']['state']
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if status == "play":
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@ -97,6 +163,7 @@ def display():
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backlight.rgb(255, 0, 0)
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lcd.create_char(0, char_stop)
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# Tests if there is some new text to display, including nothing.
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if status not in {'play','pause'} or song_file != arg['song']['file']:
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song_file = arg['song']['file'] if 'file' in arg['song'].keys() else ''
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title = arg['song']['title'] if 'title' in arg['song'].keys() else ''
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@ -120,6 +187,8 @@ def display():
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lcd.write(album)
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except queue.Empty:
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# Is this code is executed, it means that no new MPD event
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# has occured, so an exception were thrown after the timeout.
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if len(title) > 15:
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if step_title == 0 and delay_title > 0:
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delay_title -= 1
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@ -142,6 +211,7 @@ def display():
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if delay_album == 0:
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delay_album = rotate_pause
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# Redraw everything.
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if len(title) > 15:
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lcd.set_cursor_position(1, 0)
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lcd.write(stringrotate(title, 15, step_title))
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@ -153,7 +223,14 @@ def display():
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lcd.write(stringrotate(album, 16, step_album))
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lcd.clear()
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@nav.on(nav.BUTTON)
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# These functions are event handlers related to the joystick.
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# Each time the button is used, the matching function will be
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# executed. That said, because the python-mpd2 library isn't
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# thread-safe, we need to open a client for each event.
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# This is ugly as fuck.
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@ nav.on(nav.BUTTON)
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def button_center(pin):
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client = MPDClient() # Please close your eyes
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client.connect("localhost", 6600) # Dirty dirty dirty...
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@ -178,7 +255,11 @@ def button_right(pin):
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client.close() # Okay, you can open your eyes
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def on_exit(sig, func=None):
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'''
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Basically, close everything before quitting.
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'''
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run_event.clear()
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# Join the threads
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t_display.join()
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t_vumeter.join()
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backlight.rgb(0, 0, 0)
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@ -187,11 +268,11 @@ def on_exit(sig, func=None):
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sys.exit(0)
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lcd.set_contrast(50)
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run_event = threading.Event()
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run_event.set()
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client = MPDClient()
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client.connect("localhost", 6600)
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# Launch the threads
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t_display = threading.Thread(name='display',target=display)
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t_vumeter = threading.Thread(name='vumeter',target=vumeter)
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t_display.start()
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