Re: BBB IIO ADC access not working

[Michael Welling <mwelling@ieee.org>]

On Thu, Aug 20, 2015 at 01:21:17PM -0700, Greg Wilson-Lindberg wrote:
>  
> 
> > -----Original Message-----
> > From: Michael Welling [mailto:mwelling79@gmail.com] On Behalf 
> > Of Michael Welling
> > Sent: Thursday, August 20, 2015 12:23 PM
> > To: Greg Wilson-Lindberg
> > Cc: Daniel Baluta; linux-iio@vger.kernel.org
> > Subject: Re: BBB IIO ADC access not working
> > 
> > On Thu, Aug 20, 2015 at 11:41:03AM -0700, Greg Wilson-Lindberg wrote:
> > >  
> > > 
> > > > -----Original Message-----
> > > > From: Michael Welling [mailto:mwelling79@gmail.com] On Behalf Of 
> > > > Michael Welling
> > > > Sent: Thursday, August 20, 2015 10:31 AM
> > > > To: Greg Wilson-Lindberg
> > > > Cc: Daniel Baluta; linux-iio@vger.kernel.org
> > > > Subject: Re: BBB IIO ADC access not working
> > > > 
> > > > On Thu, Aug 20, 2015 at 10:27:30AM -0700, Greg 
> > Wilson-Lindberg wrote:
> > > > > 
> > > > > 
> > > > > > -----Original Message-----
> > > > > > From: Greg Wilson-Lindberg
> > > > > > Sent: Thursday, August 20, 2015 9:19 AM
> > > > > > To: 'Michael Welling'
> > > > > > Cc: Daniel Baluta; linux-iio@vger.kernel.org
> > > > > > Subject: RE: BBB IIO ADC access not working
> > > > > > 
> > > > > >  
> > > > > > 
> > > > > > > -----Original Message-----
> > > > > > > From: Michael Welling [mailto:mwelling79@gmail.com] On
> > > > Behalf Of
> > > > > > > Michael Welling
> > > > > > > Sent: Thursday, August 20, 2015 9:14 AM
> > > > > > > To: Greg Wilson-Lindberg
> > > > > > > Cc: Daniel Baluta; linux-iio@vger.kernel.org
> > > > > > > Subject: Re: BBB IIO ADC access not working
> > > > > > > 
> > > > > > > On Thu, Aug 20, 2015 at 08:50:28AM -0700, Greg
> > > > > > Wilson-Lindberg wrote:
> > > > > > > >  
> > > > > > > > 
> > > > > > > > > -----Original Message-----
> > > > > > > > > From: Michael Welling [mailto:mwelling79@gmail.com] On
> > > > > > Behalf Of
> > > > > > > > > Michael Welling
> > > > > > > > > Sent: Wednesday, August 19, 2015 2:43 PM
> > > > > > > > > To: Greg Wilson-Lindberg
> > > > > > > > > Cc: Daniel Baluta; linux-iio@vger.kernel.org
> > > > > > > > > Subject: Re: BBB IIO ADC access not working
> > > > > > > > > 
> > > > > > > > > On Wed, Aug 19, 2015 at 02:34:39PM -0700, Greg
> > > > > > > Wilson-Lindberg wrote:
> > > > > > > > > > 
> > > > > > > > > > So, in that case, can I just open it once and
> > > > leave it open?
> > > > > > > > > 
> > > > > > > > > Yes.
> > > > > > > > > 
> > > > > > > > > > Is it reading from a buffer, or is it reading what is
> > > > > > > > > current in the ADC? 
> > > > > > > > > 
> > > > > > > > > It is the current reading.
> > > > > > > > > 
> > > > > > > > > > Can I just set up a timer to get readings to 
> > average then?
> > > > > > > > > 
> > > > > > > > > Sure.
> > > > > > > > > 
> > > > > > > > > Here are some helper functions:
> > > > > > > > > 
> > > > > > > > > int iio_adc_open_channel(int dev_num, int chan_num) {
> > > > > > > > > 	char filename[255];
> > > > > > > > > 
> > > > > > > > > 	sprintf(filename,
> > > > > > > > > "/sys/bus/iio/devices/iio:device%d/in_voltage%d_raw",
> > > > > > > > > 			dev_num, chan_num);
> > > > > > > > > 
> > > > > > > > > 	return open(filename, O_RDONLY); }
> > > > > > > > > 
> > > > > > > > > int iio_adc_read_channel(int fd) {
> > > > > > > > > 	int count;
> > > > > > > > > 	char buffer[255];
> > > > > > > > > 	int value = -1;
> > > > > > > > > 
> > > > > > > > > 	lseek(fd,0,SEEK_SET);
> > > > > > > > > 
> > > > > > > > > 	count = read(fd, buffer, 255);
> > > > > > > > > 
> > > > > > > > > 	if (count > 0)
> > > > > > > > > 		value = strtoul(buffer, NULL, 10);
> > > > > > > > > 
> > > > > > > > > 	return value;
> > > > > > > > > }
> > > > > > > > > 
> > > > > > > > > Example usage:
> > > > > > > > > 
> > > > > > > > > int fd;
> > > > > > > > > .
> > > > > > > > > .
> > > > > > > > > 
> > > > > > > > > fd = iio_adc_open_channel(0, 4); .
> > > > > > > > > .
> > > > > > > > > 
> > > > > > > > > while (1)
> > > > > > > > > {
> > > > > > > > > 	printf("ADC = %x\n", 
> > iio_adc_read_channel(fd)); }
> > > > > > > > > 
> > > > > > > > > 
> > > > > > > > 
> > > > > > > > I converted to using this interface and left the
> > > > system running
> > > > > > > > overnight and the touch screen was locked up this morning.
> > > > > > > 
> > > > > > > This is without any modifications to the kernel?
> > > > > > > 
> > > > > > 
> > > > > > This was still running the kernel modifications.  I've
> > > > restarted it
> > > > > > this morning without the kernel modifications.
> > > > > 
> > > > > I just dumped what I'm reading from the sys fs and all I'm
> > > > getting back is -1.
> > > > 
> > > > Are you doing error checking on the file descriptor on open?
> > > > > 
> > > > 
> > > 
> > > You were right, I had gone back to the original kernel that RCN 
> > > shipped with the image and it doesn't export /sys/bus/iio.
> > > 
> > > I rebuilt the 3.14.49-ti-r62 kernel, which is the same 
> > release as the kernel in the image, but it does export 
> > /sys/bus/iio, so that much is working better.
> > > 
> > > But (there's always a but, isn't there), I'm reading three channels 
> > > from the ADC, 4, 5, & 6. Channel 4 gets a good reading maybe 60% of 
> > > the time I read it. Channel 5 gets a good reading maybe 
> > every 40-50 tries. Channel 6 hardly ever gets a good reading.
> > > 
> > > I guess I could just loop if I get a busy response, 
> > although I don't 
> > > know how many times I will get that return before I get a 
> > good reading.
> > >
> > 
> > What is the indicator that the reading is bad?
> >  
> 
> I get back -1 if the channel is busy.
> I just put in a loop and for channel 4 I get either 1 or 2 tries to get a good 
> sample. Channels 5 & 6 are always returning a good sample on the second read.
> 
> I'll have to leave this on for overnight to see if the touch screen will lock up.

You could try adding a poll to the read function to wait for readings to be ready.

int iio_adc_read_channel(int fd)
{
	int count;
	char buffer[255];
	int value = -1;
	struct pollfd pfd;

	pfd.fd = fd;
	pfd.events = POLLIN;
	pfd.revents = POLLIN;

	lseek(fd,0,SEEK_SET);
	poll(&pfd, 1, -1);
	count = read(fd, buffer, 255);

	if (count > 0)
		value = strtoul(buffer, NULL, 10);

	return value;
}