I am playing FM radio and trying to change the frequency of my RTL-SDR for my Raspberry Pi 3, while streaming (ie, without having to shut down the program and restart)
It currently plays the station and I can increment the station/frequency slowly. However, if I increment it too fast, the SDR stops playing.
I'm using:
My code is currently:
import os
import time
import subprocess
from pi_encoder import *
def updateStation(station_addr, kill=0):
print 'creating pipe1a'
pipe1a = subprocess.Popen(['rtl_fm', '-M', 'wbfm', '-f', str(station_addr) + 'M', '-g', '10'], stdout=subprocess.PIPE)
print 'creating pipe1b'
pipe1b = subprocess.Popen(['play', '-r', '32k', '-t', 'raw', '-e', 's', '-b', '16', '-c', '1', '-V1', '-'], stdin=pipe1a.stdout, stdout=subprocess.PIPE)
print 'creating pipe1c'
pipe1c = pipe1b.stdout
pid_a = pipe1a.pid
return pid_a, pipe1a
# Export LD_LIBRARY_PATH; doesn't seem to retain
os.system('export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib')
## Rotary encoder GPIO PIN assignments are set in 'pi_encoder' module
## SET INITIAL VALUES
tuner_value = 0
station_addr = 95.1
max_tuner_addr = 109.1
min_tuner_addr = 88.0
## INITIALIZE ROTARY ENCODER WORKER THREAD
tuner_encoder = EncoderWorker(SwitchEncoder(TUNER_CLK_PIN, TUNER_DT_PIN, TUNER_SW_PIN))
tuner_encoder.start()
## MAIN LOOP
try:
print 'Starting main loop'
pid, process = updateStation(station_addr)
while True:
delta_tuner = tuner_encoder.get_delta()
if delta_tuner!=0:
tuner_value = tuner_value + delta_tuner
print "tuner value", tuner_value
station_addr = station_addr + (delta_tuner/10.0)
if station_addr > max_tuner_addr:
station_addr = max_tuner_addr
elif station_addr < min_tuner_addr:
station_addr = min_tuner_addr
print 'station_address: ', station_addr
print 'terminating process:'
process.terminate()
try:
os.kill(pid, 0)
process.kill()
except OSError, e:
print 'Terminated gracefully'
pid, process = updateStation(station_addr)
if tuner_encoder.get_upEvent():
print "tuner up!"
if tuner_encoder.get_downEvent():
print "tuner down!"
finally:
print 'Cleaning up GPIO...'
IO.cleanup()
Is python subprocess tolerant to this use?
Is there another way (command, method, library) that would allow a more smooth and quick change of station/frequency that wouldn't affect play or stop the SDR from playing?
You may need to find a way wait for process.kill() to finish and the pipes to close (it happens asynchronously), before starting the a new process with your updateStation call. Try putting a small delay in your main while() loop after any kill to prevent it from sending process commands faster than the OS can reliably handle.
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