[PD-dev] while loop segfault

[Martin Peach]

Ah I see...
In your code you're calling gettimeofday() repeatedly while the pulse is
arriving. This will freeze Pd for the duration of the pulse. Maybe that's
what causes the segfault?
You could use a clock callback in Pd to check for the echo, but then your
resolution is down to Pd's event loop period.
Alternatively start a new thread to measure the pulse and use a clock to
check for the thread result. That way you'll get the most accurate time.

Martin

On Tue, Oct 14, 2014 at 2:21 PM, Colet Patrice <colet.patrice at free.fr>
wrote:

>  Le 14/10/2014 19:51, Martin Peach a écrit :
>
> Oh sorry, I thought you were using an arduino.
>
>
> I'm using an emulated arduino, it's called pcduino and it's the most
> powerfull miniPC we can actually find.
> PureData is running so fine on it even through ssh there is no latency
> like I've encountered on raspberry,
> and Multitrack USB soundcards runs greatly on it.
>
>
>  Martin
>
> On Tue, Oct 14, 2014 at 1:16 PM, Colet Patrice <colet.patrice at free.fr>
> wrote:
>
>>  Le 14/10/2014 15:06, Martin Peach a écrit :
>>
>>  Not sure why it segfaults, just want to say that that method is really
>> bad. Because of Pd's control rate as well as the serial interface latency,
>> your timing will be really sketchy. The way to do what you want is to
>> implement the ranging entirely on the arduino and send the values back to
>> Pd via [comport]. So a Pd [pulseIn] object shoud simply send a request to
>> the arduino to start a pulse and return the time. It could be implemented
>> as an abstraction containing [comport].
>>
>>
>>  I'm not using serial to read gpio state but fopen() (may be fopen() is
>> not fast enough), like in a raspberry (but it's not on raspberry), I will
>> try to do this with python and use pdsend for retrieving value into
>> puredata.
>> thank you for the advice.
>> pc
>>
>>
>>  Martin
>>
>> On Mon, Oct 13, 2014 at 9:29 PM, Colet Patrice <colet.patrice at free.fr>
>> wrote:
>>
>>> Hello, I'm trying to implement the pulseIn() function we can find in
>>> arduino libraries into an external.
>>>
>>> I couldn't make it work because some part doesn't seem to behave like I
>>> expect so I'm wondering if it's caused by puredata process,
>>> so maybe someone in the list could enlight me about that.
>>>
>>> The purpose of the external is about using an ultrasound sensor
>>> connected on gpio that require a microsecond timer for getting distance
>>> like this:
>>>
>>>
>>> //here is a custom timer using a struct provided by pcduino headers:
>>> #include core.h
>>> unsigned long pat_micros() {
>>>     struct timeval tv;
>>>     gettimeofday(&tv,NULL);
>>>     return tv.tv_sec*(uint64_t)1000000+tv.tv_usec;
>>> }
>>>
>>> //here is the custom pulseIn() function:
>>> unsigned long pat_pulseIn(t_pdpcduino *x, int pin)
>>> {
>>>     unsigned long timeout = 100000;
>>>     unsigned long start = pat_micros();
>>>
>>>     while( pdpcduino_gpio_read2 (x, pin) == 1 )
>>>         if( pat_micros() - start > timeout )
>>>             return 0;
>>>
>>> // this is where I'm getting a segmentation fault:
>>>
>>>     while ( pdpcduino_gpio_read2 (x, pin) == 0 )
>>>         if( pat_micros() - start > timeout )
>>>         return 0;
>>>
>>> //...
>>>     unsigned long value = pat_micros();
>>>
>>>     while( pdpcduino_gpio_read2 (x, pin) == 1 )
>>>         if( pat_micros() - start > timeout )
>>>             return 0;
>>>
>>>     return pat_micros() - value;
>>>
>>> }
>>>
>>> //...
>>>
>>>
>>> If I reduce the timeout number, segfault comes randomly after this
>>> function has been triggered, so I'm wondering if this method is really
>>> appropriate,
>>> is there an exemple of external (containing such while loops) I could
>>> get inspired from to write this pulseIn() function?
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Pd-dev mailing list
>>> Pd-dev at lists.iem.at
>>> http://lists.puredata.info/listinfo/pd-dev
>>>
>>
>>
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.puredata.info/pipermail/pd-dev/attachments/20141014/06bf9ac5/attachment-0001.html>