At some point, can you come back and try with the newer 3.0 kernels
and mainline u-boot and report if any issues keeping you from setting
the pinmux from the kernel are still there? Or, at least, could you
provide a bit of debug information on the trouble you did see? We
should only be relying on u-boot for a start-up mux setting and
reconfiguring the mux in the kernel should be a reasonable thing to
expect we can do.
> However, I was able to set it from u-boot. Watch
> out though, in u-boot, board/ti/beagle/beagle.h defines the pins in multiple
> places so you have to be sure to set them in the correct places.
> --Mark
> [1] http://elinux.org/EBC_Exercise_04_Pulse_Width_Modulation
> [2] http://elinux.org/BeagleBoardPinMux
It is a start! I'd say this is a somewhat interesting (due to the
clear exercise material) though not particularly thorough job of
covering the topic of PWM on the BeagleBoard. It does show some
specific working code from userspace given a certain kernel and system
build, but I suspect the treatment is not complete enough for typical
new users to debug their issues outside of your given starting point.
Is there a chance you can talk more about the structure of the timers
and give some analysis on the limitations of using GPIOs vs. different
types of timers?
There is some interesting and not completely thought out discussion
on-going regarding the best API for performing PWM in Linux. I
believe the hacks being done in userspace to directly program the
timer aren't the best to enable your documentation to work on new
platforms, to ease newbie issues or to simplify userspace software
that extends beyond the PWM capabilities (such as limited number of
I/Os) the hardware timers provide. The ePWM controllers on the AM1808
would be an interesting contrast.
Is there a chance you can give a bit of treatment to the PWM proposals
from Bill Gatliff [3] and Sasha Hauer [4]?
[3] http://git.billgatliff.com/pwm.git/?p=pwm.git;a=commit;h=a49cbfff0fa09bff40d328f8985a0a7a7b951d6f
[4] http://git.pengutronix.de/?p=imx/linux-2.6.git;a=commit;h=137654cde98a2ffe548f47f02e7fde512bc2091c
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Hi Mark,
Thanks for sharing and I hope to see more exercise towards writing
device drivers for the platform for the various buses. i.e. i2c, spi,
uart, pci etc..
Using the TC74 should be a good start for this exercise.
I'm a newbies and hope to see more of such exercises and tutorials to
clear the mystery behind writing such device driver that are commonly
encountered in embedded project. Writing for MCU is direct but with an
OS is a different learning curve.
Cheers~!
--
Regards,
James
I've added a TutorialWishlist page for compilation of Tutorials that
people would like to see:
http://elinux.org/TutorialWishlist
>
> Using the TC74 should be a good start for this exercise.
>
> I'm a newbies and hope to see more of such exercises and tutorials to
> clear the mystery behind writing such device driver that are commonly
> encountered in embedded project. Writing for MCU is direct but with an
> OS is a different learning curve.
>
> Cheers~!
>
> --
> Regards,
> James
>