Timing issue with analog reads

[ghost]

Hi,

I could not manage to setup a reliable connection between my pc and arduino (standard firmata sketch). The confusing part is that it all seems to work in the python command line, but when running the example code in a small script, analog reads return 'None'. After inserting a little pause (emulating manual execution in the python shell), analog read does output some values.

Here's my test-script:

#!/usr/bin/env python
import time
from pyfirmata import Arduino, util
board = Arduino('/dev/ttyUSB0')
it = util.Iterator(board)
it.start()
board.analog[0].enable_reporting()
print board.analog[0].read()
print board.analog[0].read()
print board.analog[0].read()
print board.analog[0].read()
time.sleep(1)
print board.analog[0].read()
print board.analog[0].read()
print board.analog[0].read()
print board.analog[0].read()
board.exit()

...and it's output:

None
None
None
None
0.6354
0.6354
0.6354
0.6354

As mentioned, when just typing the statements in the python shell it just seems to work fine:

>>> import time
>>> from pyfirmata import Arduino, util
>>> board = Arduino('/dev/ttyUSB0')
>>> it = util.Iterator(board)
>>> it.start()
>>> board.analog[0].enable_reporting()
>>> print board.analog[0].read()
0.6129
>>> print board.analog[0].read()
0.567
>>> print board.analog[0].read()
0.5787
>>> print board.analog[0].read()
0.607
.... etc

Used hard-/software:
pyFirmata 0.95 in python 2.7.3
Firmata 2.3.5 on an Arduino duemilanova (ATmega328 version)

Any clue?

Bests,

Bram

[tino]

The iterator thread updates the values of the pins, and has a little sleep time in there (https://github.com/tino/pyFirmata/blob/master/pyfirmata/util.py#L42). It is probably that that update has not run yet when you read the values. Could you try this instead of your reads and time.sleep(1):

start = time.time()
while board.analog[0].read() is None:
    print "nothing after {0}".format(time.time() - start)
print "first value after {0}".format(time.time() - start)

That will probably tell you how long you have to wait.

[ghost]

Hi Tino,

Thanks! The first value is returned after around 22ms.
I can do this in my code.

If I try to fix it in util.py, by changing the little sleep time of 1ms to 50ms, I get:

...
...
nothing after 0.0590040683746
first value after 0.0655460357666
0.739
0.739
0.739
0.739
0.739
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 552, in __bootstrap_inner
    self.run()
  File "/usr/local/lib/python2.7/dist-packages/pyfirmata/util.py", line 40, in run
    while self.board.bytes_available():
  File "/usr/local/lib/python2.7/dist-packages/pyfirmata/pyfirmata.py", line 225, in bytes_available
    return self.sp.inWaiting()
  File "/usr/local/lib/python2.7/dist-packages/serial/serialposix.py", line 435, in inWaiting
    s = fcntl.ioctl(self.fd, TIOCINQ, TIOCM_zero_str)
TypeError: argument must be an int, or have a fileno() method.

That's obviously not the right place to wait.

At least I can produce some working code now!

Groetjes,

Bram

[tino]

The easiest is probably to just read and test for None

[ghost]

I've done exactly that. But when reading digital ports at the same time, it gives me nothing but None's ;-(
I'll post a short script later.
Have people been using pyFirmata successfully with firmata 2.3.5 on a Arduino Duemilanova?
BTW, do you have some example code available?

[tino]

What do you mean by "reading digital ports at the same time"?

This is the only example I could find quickly. It is not that easy though...
https://gist.github.com/tino/5673806

[tino]

Closing, as I can't move forward with this. Hopefully it's not a problem anymore!