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 beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
