On Sat, 30 Jan 2016 15:52:12 +0100 Neil Armstrong <narmstrong@xxxxxxxxxxxx> wrote: > 2016-01-30 5:26 GMT+01:00 David Rivshin (Allworx) > <drivshin.allworx@xxxxxxxxx>: > > From: David Rivshin <drivshin@xxxxxxxxxxx> > > > > When using a short PWM period (approaching the min of 2/clk_rate), > > pwm-omap-dmtimer does not produce accurate results. In the worst > > case a requested period of 2/clk_rate would result in a real period > > of 4/clk_rate instead. This is a series includes a fix for that > > problem, as well as other related improvements, and is based on the > > current linux-pwm/for-next tip. > > > > I have tested on a Sitara AM335x platform, using a scope to verify > > the output with a variety of periods and duty cycles. This includes > > a PWM rate up clk_rate/2 with 50% duty cycle (e.g. generating > > fclk/2) with both 32768Hz and 24MHz fclks. I do not have an OMAP4 > > board to test with, although appropriate sections in the the > > reference manuals appear substantially the same, so I believe the > > changes are equally correct there. > > > > Note that the OMAP4 TRMs do effectively state that the maximum PWM > > rate is clk_rate/4, so at very fast PWM rates the behavior may not > > be as reliable as I observed with Sitara. Although I suspect that > > it's the same module and will also work, at least under some > > circumstances. If anyone with OMAP4 hardware and a scope is so > > inclined, I would be curious to know the results. > > Hi David, > > Thanks for the work, it seems all good, I'll test them on my side the > next days, but this work needed to be done for sure ! Thanks to you (and everyone else involved) for doing the heavy lifting on the driver to begin with. It came just as I had a need for the PWM output of a dmtimer, and came to the conclusion that just such a timer-to-PWM adapter was needed. > The only OMAP4 HW I have is a Pandaboard and it's very difficult to > get the timer outputs... For what its worth, I took a quick look at the Pandaboard Rev EA1 schematic, and I can see how it doesn't make using a timer PWM output easy. Easiest option I found might be to change the pinmux for AG24 (h_GPIO_121) to be DMTIMER11_PWM_EVT, and probe it at S2 or J13. -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
