From: Felipe B. C. <cav...@gm...> - 2009-02-21 23:07:53
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On Fri, Feb 20, 2009 at 4:40 PM, Dave Hylands <dhy...@gm...> wrote: > Hi Felipe, > > > Is there any way to directly access the PXA270 registers from the user > > space? > > I am writing a real-time application using Xenomai and I need to have > access > > to the UARTs, bypassing the kernel entirely in order to keep the > latencies > > low. > > You can mmap any of the registers in. I'm not sure how successfull > your attempts will be. Note that while you'll be able to access the > registers from user space, you won't be able to write interrupt > handlers. > > See the pxaregs program for examples of using mmap to map int the > registers directly. > > If you're going directly to the HW, you'll need to disable the kernel > drivers so that they don't try to access the registers at the same > time. I did try to do so without success - but my kernel drivers were enabled. I will try to disable them and see what happens. > > > > I tried to write an application that reads/writes directly to the proper > > registers (based on the program found at > > http://docswiki.gumstix.com/index.php/Sample_code/C/gpregs), yet I can't > get > > a proper reading from the said UART. > > If you didn't disable the kernel drivers, then they'll be sucking up > the characters before your user mode program can get to them (there's > no way user mode will beat the interrupt handler). The context > switching overhead will (I believe) make accessing registers directly > less efficiently than can be done from kernel space. > Hm.. it seems them that maybe writing a real-time driver for the UARTs is the way to go than - it should keep my latencies lower. Thanks for the help, Dave! BTW, if anyone is interested, the idea is to make it communicate with a Bioloid humanoid robot in real-time, so it can do the motion planning/balance control in real time. > > -- > Dave Hylands > Shuswap, BC, Canada > http://www.DaveHylands.com/ > > > ------------------------------------------------------------------------------ > Open Source Business Conference (OSBC), March 24-25, 2009, San Francisco, > CA > -OSBC tackles the biggest issue in open source: Open Sourcing the > Enterprise > -Strategies to boost innovation and cut costs with open source > participation > -Receive a $600 discount off the registration fee with the source code: > SFAD > http://p.sf.net/sfu/XcvMzF8H > _______________________________________________ > gumstix-users mailing list > gum...@li... > https://lists.sourceforge.net/lists/listinfo/gumstix-users |