Board spins eat up weeks of project - software / firmware changes are "free". ;-)
...so the powers that be would rather see this solved at the Beaglebone rather than on our outboard hardware. And that's kind of a legitimate request, too - nobody in their right mind would design a system where Outputs go HOT without any interaction to request that state. On Wednesday, March 30, 2016 at 9:11:09 AM UTC-6, Wulf Man wrote: > > 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] <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.
