Yes, I was talking about trying to do hard real-time data collection in
a user-space program. If you look at the maximum interrupt latencies
from other stuff running on the system, then you see just why PRUs are
necessary to always meet your deadlines. Most of the time, a user-space
program running mmap to access gpios will run up at Mhz speeds but every
now and then one of your data samples might be 100 msec late because
something else was running. That kind of irregular sampling makes an
FFT worthless. (But there certainly are some slower speed control
applications where that kind of latency is perfectly okay.)
I have a program that runs the SPI0 port as a slave, and it can be
clocked by the master SPI device at 12-16 MHz because my protocol never
overflows the SPI FIFOs. I had to use mmap, so I could set SPI control
registers in ways no Linux drivers support.
On 6/5/2014 11:53 AM, Brandon I wrote:
> but you can't run the clock much faster than 1 KHz using a user-space program
under Linux.
Not true at all! You can get over 3MHz just fine with mmap to the gpio
registers. If you try to open and close a file each gpio toggle, like
the insanely inefficient sysfs interface, then yeah...you'll be
severely limited, but still much faster than 1kHz.
Did you
google? http://e2e.ti.com/support/arm/sitara_arm/f/791/t/296484.aspx
On Thursday, June 5, 2014 8:31:24 AM UTC-7, William Hermans wrote:
Sounds like fun. Good luck :)
On Wed, Jun 4, 2014 at 2:17 PM, <swapn...@gmail.com> wrote:
Hey William...
I do know that the Chip Select line can be used to toggle
between different SPI units... But I need data to be collected
simultaneously from multiple sensors... As of now I have 32
sensors - I have clubbed them into groups of 4 and so I have 8
sets of SPI units that I want to communicate with
"simultaneously"...
On Wednesday, June 4, 2014 11:46:21 AM UTC-4, William Hermans
wrote:
It sounds as though you need to read more concerning what
SPI actually *is*.
/Devices communicate in master/slave mode where the
master device initiates the data frame. Multiple slave
devices are allowed with individual slave select
lines. Sometimes SPI is called a four-wire serial bus,
contrasting with three-, two-, and one-wire serial
buses. SPI is often referred to as SSI (Synchronous
Serial Interface)./
http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus
<http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus>
What does this mean ? Multiple devices can share the same
data bus, and only CS( chip select ) needs be different
for each device. CS only needs to go high, or low, which
hey remarkably is exactly what GPIO pins do ! :)
On Wed, Jun 4, 2014 at 7:37 AM, <swapn...@gmail.com> wrote:
I am trying to run multiple SPI modules (more than the
two available on the BBB) to try and read data from a
bunch of accelerometers (LSM303D).
I was therefore wondering if it would be possible to
implement the SPI module using code (preferably C/C++)
on the abundant GPIO pins. I have been scanning
through a lot of documentation but I cant seem to find
anything that fits the bill.
Please help --- getting desperate...
--
For more options, visit http://beagleboard.org/discuss
---
You received this message because you are subscribed
to the Google Groups "BeagleBoard" group.
To unsubscribe from this group and stop receiving
emails from it, send an email to
beagleboard...@googlegroups.com.
For more options, visit
https://groups.google.com/d/optout
<https://groups.google.com/d/optout>.
--
For more options, visit http://beagleboard.org/discuss
---
You received this message because you are subscribed to the
Google Groups "BeagleBoard" group.
To unsubscribe from this group and stop receiving emails from
it, send an email to beagleboard...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout
<https://groups.google.com/d/optout>.
--
For more options, visit http://beagleboard.org/discuss
---
You received this message because you are subscribed to the Google
Groups "BeagleBoard" group.
To unsubscribe from this group and stop receiving emails from it, send
an email to beagleboard+unsubscr...@googlegroups.com
<mailto:beagleboard+unsubscr...@googlegroups.com>.
For more options, visit https://groups.google.com/d/optout.
--
For more options, visit http://beagleboard.org/discuss
---
You received this message because you are subscribed to the Google Groups "BeagleBoard" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to beagleboard+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
