On Tue, Feb 16, 2016 at 4:08 PM, John M <[email protected]> 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]. For more options, visit https://groups.google.com/d/optout.
