First of all, Thank you all for your help and suggestions. It turns out it was the fault of the oscilloscope. I found a better model and found my rates to be ~1.5ns.
In case anybody was curious, this is being designed to control a radioactive electron measurement ASIC. On Wednesday, February 17, 2016 at 12:10:00 AM UTC-5, [email protected] wrote: > > The PRU rise and fall times are 1.00 - 3.00 nSec. Your scope probe or > application circuit may be limiting the slew rate. Another possibility is > your oscilloscope input is bandwidth limited. If you are using a 1X scope > probe it will contribute significant capacitive loading and slow the edges > way down. > > Keep us informed with your progress and good luck. > > Cheers, > > Lowell Bohn > Chief Engineer > Basis Vector LLC > (303) 249-3763 > > > -----Original Message----- > *From:* Przemek Klosowski [mailto:[email protected] <javascript:>] > *Sent:* Tuesday, February 16, 2016 10:53 PM > *To:* [email protected] <javascript:> > *Subject:* Re: [beagleboard] Slew rate when toggling Enhanced GPIO pins > in the PRU? > > On Tue, Feb 16, 2016 at 4:08 PM, John M <[email protected] <javascript:>> > wrote: > >> I'm trying to create a clock using the PRU, and I have it working to an >> extent, but I am noticing a discrepancy between what I read in the TRM and >> what I'm seeing. When I use a series of SET CLR SET CLR commands on a pin, >> they do not resolve completely before the next command. When I seperate >> each command by a delay, the rising edge of the clock takes ~90ns to go >> from 0V to 3.3V. I was under the impression that this operation would be >> performed at around ~5ns. >> > > Straight out Set/Clear would theoretically run at 100MHz (two > instructions of 5ns each), but when you connect them to the chip I/O, there > are effects of interconnect between the PRU and the I/O resources, Charles > Steinkuehler wrote it up in > https://github.com/machinekit/machinekit/blob/master/src/hal/drivers/hal_pru_generic/pru_generic.p > > > However, the rise time of the signal as seen by your oscilloscope is > totally unrelated to that: the signal on a pin should change within a IO > clock cycle and the skew you're seeing must be due to the RC(L) delays due > to factors such as the state of the pullup on the IO pin, capacitances and > inductances within the package, on your board and in your oscilloscope > probe and cable. > > > -- > 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 [email protected] <javascript:>. > 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
