Hi José,
Thank you for your post. You are correct that it is a feature of the
Arduino architecture that a transition on RTS resets the target
microcontroller to enable automatic programming, and it is possible to
disable this feature, either as you describe or by removing the capacitor
which couples RTS to Reset. However, as I intend to make my Web2py
application available to others in the future, and they may choose to use
standard Arduino products to implement the radio transmitter then I was
keen to avoid any hardware modifications, especially as these will
inevitably lead to support questions! Also my USB radio dongle is enclosed
in a plastic case which would have to be opened to reprogram the code.
I also agree that it is not strictly a Web2py 'problem', except that I am
using Web2py and the problem is as a result of using the serial port in a
background process running under its Scheduler - and the observation that
when Web2py saves and parses files it does something to the serial port
which overcomes the problem and I was hoping to find out what that was and
make use of it. However, I have since found a solution using a script,
installed during the boot sequence which holds the serial port open. I
created a file 'OpenPort.py' which contains the following code:
import serial
import time
ser=serial.Serial('/dev/ttyUSB0', 57600, timeout=1, xonxoff=0, rtscts=0)
ser.rts=True
while 1:
time.sleep(0.0001)
This is called from a bash script installed using 'sudo update-rc.d
scheduler-openport defaults' which contains the lines:
dir="/home/www-data/web2py"
user="www-data"
cmd="sudo nohup python
applications/Heating_Controller/utilities/OpenPort.py &"
I put the file in a new 'utilities' directory under my application as I
wanted it to be part of the application's files but it cannot be in
a directory that Web2py recognises (such as Models or Modules) because
OpenPort.py remains open which prevents the Admin interface from working.
This has solved my problem and doesn't have any hardware implications.
Richard
On Tuesday, December 6, 2016 at 5:25:55 PM UTC, José L. wrote:
> Hi Richard, maybe I'm wrong, but I think this is not related to web2py at
> all.
> Arduino boards are build to make a reset whenever the port is open/reopen
> so they change to "programming" state.
> This is made on purpose, but it's trivial to avoid it. If using an Arduino
> UNO board, just connecting a 10μF capacitor between RESET and GND will
> avoid those resets. Just remember to remove the capacitor if you need to
> re-program your board.
>
> Hope this was the issue.
> José L.
>
> 2016-11-26 16:58 GMT+01:00 Richard Brown <[email protected] <javascript:>>:
>
>> I've now had chance to do some more investigation and research since my
>> last posting and found the following. The reason that saving files in
>> Web2py causes RTS to be asserted and makes my application work is that my
>> file 'control.py', which contains all my serial functions, includes the
>> lines:
>>
>> import serial
>>
>> ser=serial.Serial('/dev/ttyUSB0', 57600, timeout=1, xonxoff=0, rtscts=0)
>>
>>
>> If I remove/comment out the line 'ser=serial.Serial... ' then the file
>> save has no effect. Presumably Wb2py must be executing this line somehow as
>> part of it's parsing process, and saving my other file 'utilities.py' has
>> the same effect because it contains 'import * from control.py'.
>>
>> I have also been playing with the Pyserial functions ser.setRTS() and
>> ser.rts, which should force the state of RTS. I have been running these
>> from Python scripts in my user account and found that if reboot the
>> Pi, save one of the files in Web2py to force RTS low, then execute ser.rts
>> or ser.setRTS using my scripts, I can set RTS high or low and that state
>> persists. However, if I reboot the Pi and run my script *without* saving
>> the files in Web2py then run my scripts it only cause RTS to pulse low
>> momentarily, presumably while the script is running. I've tried including a
>> similar script within the Web2py 'modules' area, I've tried including the
>> set.rts commands within my serial functions, I've tried a separate function
>> just to include that command but nothing has done anything other than pulse
>> RTS until the script/function ends. I haven't tried running a routine once
>> at startup yet, but I'm not sure how this will be different from running
>> scripts 'by hand', except as far as I am aware I cannot run scripts as
>> the 'www-data' user as there is no login/password for that account, and I
>> have a strange feeling that there must be some sort of ownership issue
>> here. I have written/hacked scripts to run at startup to start the Web2py
>> Scheduler and GPIOSever but this is all a bit close to the limits of my
>> knowledge and ability!
>>
>> In summary, I am further forward in the sense that I understand why, if
>> not how, Web2py file saves make my application work, although not why
>> RTS gets set permanently low by this mechanism and not when the serial port
>> is opened at any other time, and more information on what is happening here
>> would be useful. I also know that there is a mechanism for changing the
>> state of RTS, which it must be possible to do somehow, but have no real
>> idea how to do it. I also now believe that keeping the port permanently
>> open is not necessary, provided RTS can be forced low.
>>
>> So, any clues as to how I might be able to set RTS at startup will be
>> gratefully received!
>>
>> Richard
>>
>>
>>
>>
>>
>> Richard
>>
>> On Friday, November 25, 2016 at 11:10:26 PM UTC, Dave S wrote:
>>
>>>
>>>
>>> On Friday, November 25, 2016 at 4:50:34 AM UTC-8, Richard Brown wrote:
>>>>
>>>> An update to this - I have done some more investigation and discovered
>>>> that in the 'Not Working' scenario the RTS output is mostly high but goes
>>>> low whilst the port is open, and in the 'Working' scenario the RTS output
>>>> has somehow been forced low and so stays low when the port is opened.
>>>> The Dongle gets reset by a high-to-low transition of RTS, so no falling
>>>> edge, no Reset and everything works. For reference my Dongle uses an FTDI
>>>> device (FT230X) and hence the FTDI driver supplied with the latest
>>>> Raspbian
>>>> (Jessie) release.
>>>>
>>>> The question now, therefore, is how Web2py forces RTS low - either by
>>>> the saving of a file or when I access the index page of my Site, and How I
>>>> can replicate this in the Scheduler code! Using 'touch' to update the file
>>>> does not work, it has to be saved from within Web2py.
>>>>
>>>> Richard
>>>>
>>>
>>> I can't imagine how saving the file causes RTS to go low. Web2py should
>>> not have any reason to do anything to the serial port on its own, and
>>> probably doesn't even know the serial port exists (it's only concerned with
>>> the console). (I haven't done any serial port handling under Ubuntu, nor on
>>> the RaspberryPi, so I can't tell you about any special tricks such ports
>>> need.)
>>>
>>> You may want to investigate having a separate program that gets started
>>> on system startup, runs forever, and holds the serial port open all the
>>> time. It can check for a file existing, write the current value to the
>>> file, and snooze again. Your scheduled task would the create the file,
>>> wait briefly, and then read the file to get the current value.
>>>
>>> I do know someone with a RaspberryPi, and he's a bit of hacker, but it
>>> will be next week before I see him again.
>>>
>>> /dps
>>>
>>> --
>> Resources:
>> - http://web2py.com
>> - http://web2py.com/book (Documentation)
>> - http://github.com/web2py/web2py (Source code)
>> - https://code.google.com/p/web2py/issues/list (Report Issues)
>> ---
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>
>
--
Resources:
- http://web2py.com
- http://web2py.com/book (Documentation)
- http://github.com/web2py/web2py (Source code)
- https://code.google.com/p/web2py/issues/list (Report Issues)
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