Probably your only solution is a hardware solution. buffer the PRU lines with a tristate buffer and enable it when you want it enabled.
On 3/30/2016 8:00 AM, Phil Mills wrote: > I'm working with a Beaglebone Black to do some signal acquisition > using a laser as a light source. > > The sampling/acquisition system is driven through the PRU since I need > pretty tight timing - including pulsing a laser to illuminate a sample. > > A problem that we just noticed is that as soon as I load the Device > Tree overlay that maps my PRU lines, several of the outputs go HIGH > instantly - including the one that drives the laser - until the > software spins up and initializes everything back to LOW. > I'm specifically looking at pin P8-46 mapped as pr1_pru1_pru_r30_1, > but a number of pins have the same behavior. I've tried asserting the > pulldowns in the DeviceTree, but they don't have any effect, so I'm > pretty sure it's not just the signal floating up, but rather being > driven high. > > > With a laser the time it takes my software to come up and clear > everything out is a safety liability. > > > > What can I do at the Beaglebone to ensure / enforce outputs staying > LOW when the Device Tree overlay is mapped? > > > The default state of P8-46 is LOW, but I can stick a scope on it and > see it go HIGH as soon as the Device Tree overlay loads. > > > > Several web searches come up with suggestions to "rebuild uBoot to get > the pin state you want", but there's not a lot of detail on that and > nobody ever comes back to the discussions with "Yes - that did the > trick!". > I'm also not convinced that'd solve the problem since the state of the > pin post-boot is LOW - it's only when the DTree overlay loads that the > pin jumps HIGH. > > > Suggestions / Resources? > > > > -- > 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] > <mailto:[email protected]>. > 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.
