I've done some work with GPIO handshaking from a user space program, and
I've watched the process with a logic analyser: I see the user space
program running about 70% of the time with several msec gaps about every
10 msec. I also see some longer gaps (up to 120 msec!) every now and
then. Don't even try to do data collection with under 200 msec latency
requirements from unmodified linux user space. There are some kernel
mods you can get that will cut that down to about 60 usec. A better way
to go is to use a PRU (which is why they are there) or to write a
timer-based interrupt driver. That's what you need to do to collect
data at regular intervals, like for an FFT.
As for the simultaneous collection issue, the I2C broadcast command is
the way to go if your devices support a broadcast CONVERT command
followed by individual READ commands. Or maybe your sensors can all
CONVERT on receiving a single GPIO signal?
On 9/21/2014 8:37 PM, Cedric Malitte wrote:
Le dimanche 21 septembre 2014 17:55:42 UTC-4, Gökhan Tarim a écrit :
Hello everyone,
I have a project about earthquake and i'm using accelerometer
sensors to measure earthquake data. But I have a problem with that.
I want to measure two accelerometer sensors that support I2C with
Beaglebone Black at the same time but these sensors will be
different I2C port and
The timing is so important for me. I have to take all data from
sensors at the same time. I readed some article about that
situation and mostly people using
MCU that support RTOS but I'm using Linux kernel.
So is it possible with software ? and how should i do ?
Thank you for responses.
Hi,
As Charles mentioned, you did not tell which sensors you are using.
Why could not the sensors be on the same bus ?
On the same bus, you could broadcast a message to start conversion.
see http://www.i2c-bus.org/addressing/general-call-address/
Derek Moloy got interesting videos too :
https://www.youtube.com/watch?v=8C2zk6B-eLU
That said, I am also working on time critical AD conversion for
accelerometers in order to measure displacement, thus integration of
accelerometers data and I need to have a precise time interval.
I first tried using Gpio from userland but timing was out of control.
This is why I'm trying to use the PRUs units to control the ADCs
Regards,
Cedric
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