BTW, caught this posting https://forum.beagleboard.org/t/gpio-export-problem/29737
Apparently exporting twice to the same pin will cause it to go away. If I understand the issue correctly. All the more reason to test to see if it's already there and then not export if so. John > -----Original Message----- > From: beagleboard@googlegroups.com [mailto:beagleboard@googlegroups.com] On > Behalf Of John Dammeyer > Sent: May-18-21 10:40 AM > To: beagleboard@googlegroups.com > Subject: RE: [beagleboard] Re: Using GPIOs without Using sudo > > Hi Dennis, > > Suggest > > > > if (not (IsPinBitSet(Pin, ExportedBitmask) > > or IsPinBitSet(Pin, ExportDefinedBitmask)) then begin > > > > That way you don't waste time with the TryReadCharFromFile() if you already > > know it was externally exported. > > The ExportDefinedBitmask I created is the only extra bit available in that > array of bytes indexed by pin number. But like the > ExportedBitmask it's unknown until the system tries to read from it at which > point it's defined. I added it because I didn't think any > application has the right to unexport a pin that was already exported on > start up. > > Even with just the 1/2 second delay, you can see the difference in speed of > the test application when the pin is already exported > compared to when it's not. > > > > > > > > > > I'd put the delay immediately after > > > > // Wasn't exported when program started so now let's export it. > > if TryWriteTextToFile(FExportFileName, IntToStr(Pin)) then > > begin > > SetPinBit(Pin, ExportedBitmask); > > *** put delay statement here ***; > > end; > > > Yes. Could be put there too. I'll take a closer look to see if that > introduces a side effect. I had a reason for not doing it in the export > procedure. Just don't remember why... > > > > > > > > > > > >The only issue I've run into is the repeat until loop. Seems like the > > >file is readable in about 100mS but fails with the write unless > the > > delay is 500mS. > > > > > > > Which "file" (there are so many created under each exported pin) <G> > > The initial usage of the pin must be to set the direction which then does the > export so that's the file I try and read from. Trying to get > pin value before setting direction results in a fault. > > > > > > It may be that the OS default for those files permits reading -- but > > the group hasn't been changed yet so only root can write. Sometime after > > the creation, the logic that sets up special groups runs and changes the > > file to a group that allows you to write. > > Hmm. Maybe it's better to try and get the file attributes and then it would > execute the loop decrement section instead. At the > moment it never executes that part of the code. > > In either case I just need to test that code on the Pi3 and Pi4 to make sure > Blinky blinks. On the Beagle the code now makes it > through the Reset and DIR select for the SPI bus test code but dies on the > IOCTL call. > > The simple C code in the > \\BEAGLEBONE\debian\exploringBB\chp08\spi\spidev_test does work so the > question is what's broken in > the pxl library? > > And now that I have the Mikroe Click board rewired I have two beagles with > CAN bus drivers in the kennel. > > I have a Click board with a SPI based RAM chip which will be the easiest to > interface with rather than a breadboard with an SPI > 320x240 LCD SPI controlled display. > > Baby steps eh? > John > > > > > > > -- > > Dennis L Bieber > > > > -- > > 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. > > To view this discussion on the web visit > > https://groups.google.com/d/msgid/beagleboard/40a7ag9gv2635mshemm4euqic4370aodfr%404ax.com. > > -- > 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. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/011e01d74c0c%24e13144e0%24a393cea0%24%40autoartisans.com. -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/016c01d74c32%24d1fe2ad0%2475fa8070%24%40autoartisans.com.
