Review 9a: Atmel SMART SAMA5D4 Xplained Ultra - Set up ADC Buffer with Hardware Trigger Part 1

20 May 2015

I'm trying the Buffer and Hardware Trigger capabilities of the SAMA5D4.

I followed the instructions on IioAdcDriver < Linux4SAM < TWiki, but was struggling with one particular command.

I raised a topic on tha at91.com forum. And resolved it myself.

Sometimes writing down your problem leads to the solution.

Instructible

You can read my topic on the at91 site to see where I was in trouble. (jc: At the time of posting this blog, I didn't know yet that I would get the at91.com treatment)
In this blog, I'll post the how-to.

Poky (Yocto Project Reference Distro) 1.6.1 sama5d4-xplained /dev/ttyS0


sama5d4-xplained login: root
root@sama5d4-xplained:~# echo 1 > /sys/bus/iio/devices/iio:device0/scan_elements/in_voltage0_en
root@sama5d4-xplained:~# echo "fc034000.adc-dev0-continuous" > /sys/bus/iio/devices/iio:device0/trigger/current_trigger
root@sama5d4-xplained:~# echo 100 > /sys/bus/iio/devices/iio:device0/buffer/length
root@sama5d4-xplained:~# echo 1 > /sys/bus/iio/devices/iio:device0/buffer/enable
root@sama5d4-xplained:~#

This will start the process. The ADC will now fill the character device /dev/iio:device0 with data.

How did I get the magic name "fc034000.adc-dev0-continuous"? It's different than the name "at91_adc-dev0-external" used in the AT91.com instructions.

By fiddling around a lot, and then by submitting the command

root@sama5d4-xplained:/sys/bus/iio/devices/trigger0# cat name
fc034000.adc-dev0-continuous

I still have to write a program that reads the character device.

I have already checked the source of drivers/staging/iio/Documentation/generic_buffer.c but I haven't been successful in compiling it yet.

I'll also need to learn how I can set the sampling speed.

I'd like to get 128 samples in 3.86ms. Check my previous post to understand why.

I hope that by putting this example here, I can help fellow developers started with the on-board ADC.

Top Comments

Workshopshed over 10 years ago in reply to Jan Cumps

Your efforts are valued even if not by the AT91 crew.
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Jan Cumps over 10 years ago in reply to Workshopshed

I don't need their backs. I really don't.
At the end of this exercise I want a nice design where this board plays a significant role.
But then again, I might just unplug it and put it back in its box if that's how they value the efforts here.
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Workshopshed over 10 years ago in reply to Jan Cumps

That does raise an interesting question about what actually is a "distribution".

I suspect you've got their backs up as you've not followed their "rules" for getting things built. These rules are of course not written down and are only passed on to the worthy and can be changed at will....
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Jan Cumps over 10 years ago in reply to Workshopshed

Still no joy on the at91.com forum.
How is there ever going to evolve a happy and thriving community from that??
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Jan Cumps over 10 years ago in reply to Workshopshed

I did search, and I did find that post.
Go read it: http://www.at91.com/discussions/viewtopic.php/f,33/t,24631.html
It's difficult to follow because the wits overtones are bigger than the content.

It's a theme. The user after me who posted a question got this treatement:

If that documentation would be up to the mark, I could understand that.
But it isn't up to the mark.As someone learning the subject, you're not helped by the document, and ridiculed away by the community.
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