On Thu, 23 Apr 2015 20:02:03 -0400, you wrote: inputs are not inputs are not inputs as far as loading goes.
if I connect an instrument with a 50 ohm impedance to a TTL/CMOS gate, then it's going to see low at that gate input, even though they are all inputs. Different logic series gates look like different things at the inputs. Those inputs affect the other inputs. The GPIO current out is not the issue, it's what the GPIO input sees when the circuit is booted that determines what happens. Harvey >If they cause the BBB to not boot, by hooking an input to them, I would >argue they should never have been brought out to the header, and that >examples of how to handle this sensitivity while still making use of the >header pins should be more readily available. The documentation on this >sensitivity appears to be a single poorly written paragraph in the SRM >which only states they should not be driven (actually 3 lines only in >section 7.12.1 following Fig 58; to be specific: "/If you plan to use >any of these signals, then on power up, these pins should not be driven. >//If you do, it can affect the boot mode of the processor and could keep >the processor from //booting or working correctly/." I can't see this >addressed anywhere else in the documentation). It should state that not >even inputs can not be connected to these header pins. There is no >documentation that I can see on why they were even brought out to the >header. Issues like this make other alternatives to using the BBB's look >more attractive (such as the new PI). At a minimum, this will cost us >another 4 lost weeks and $2K for new populated boards for another >iteration on our cape. Very frustrating, and I would argue both poor >design and poor documentation. Looking at the schematic, it appears the >existing load on each pin is 2 100K resistors? If this is correct, I >would not call this "well loaded" when a typical gpio output current is >4-6mA. > >On 15-04-23 02:08 PM, Gerald Coley wrote: >> ANY load can affect how they are read. These pins are already well >> loaded as it is. If you want to use them, use a buffer to isolate them >> until after the processor is running. >> >> Gerald >> >> >> On Thu, Apr 23, 2015 at 12:20 PM, Bit Pusher <[email protected] >> <mailto:[email protected]>> wrote: >> >> This is not clear as they are connected to other inputs which I >> would normally think means they are not being driven. Is there a >> definition you can give a link to defining what driven is? Also, >> can you supply a link of how to control and what are the mux >> defaults before boot? Thank you. >> >> >> On Thursday, April 23, 2015 at 12:29:26 PM UTC-4, Wulf Man wrote: >> >> you are messing with the boot pins. its been stated here 100s >> of times you cannot do anything to these pins before board boots. >> check the BBB schematic and the using the bbb board guide., >> >> >> On 4/23/2015 9:09 AM, Bit Pusher wrote: >>> I have found a reproducible boot freeze (on two boards); >>> could someone else possibly check; it's very easy to try. >>> No connections besides power plug and one (or two) wires from >>> header P8 to P9 >>> Scenario 1: connect P8-43 to P9-30, plug in power, only power >>> light comes on and BBB does not boot up >>> Scenario 2: connect P8-44 to P9-28, plug in power, only power >>> light comes on and BBB does not boot up >>> Scenario 3: connect both P8-43 to P9-30 and P8-44 to P9-28, >>> plug in power, power light and all 4 LEDs come on steady and >>> BBB does not boot up. >>> >>> Discussion: >>> 1) doing these tests numerous times on 2 BBB's did not hurt >>> either one of the boards I have, but this behavior is so >>> strange that it might be risky; please don't be upset with me >>> if it hurts your board. >>> 2) uname -a gives Linux beaglebone 3.8.13-bone70 #1 SMP Fri >>> Jan 23 02:14:42 UTC 2015 armv7l GNU/Linux. My OS version is >>> Debian wheezy 7.8 >>> 3) without wires connected, after booting and doing a >>> >sudo cat /sys/kernel/debug/pinctrl/44e10800.pinmux/pins shows >>> ... >>> pin 42 (44e108a8) 0000002f (this is P8-43 in mode 7 which >>> should be gpio2_8) >>> pin 43 (44e108ac) 0000002f (this is P8-44 in mode 7 which >>> should be gpio2_9) >>> ... >>> pin 102 (44e10998) 00000027 (this is P9-30 in mode 7 which >>> should be gpio3_17) >>> pin 103 (44e1099c) 00000027 (this is P9-28 in mode 7 which >>> should be gpio3_16) >>> >>> Therefore at boot, pins P8-43 and P8-44, without applying >>> device trees, are both configured as inputs with pull-downs; >>> pins P9-30 and P9-28, without applying device trees, are both >>> configured as inputs with pull_up/pull_down's disabled. >>> >>> 4) making the connections after boot does not have any >>> discernible effects >>> >>> 5) It seems to me that having two gpio's connected together >>> with both configured as inputs and one having a pull-down >>> should not cause the BBB to freeze at boot. >>> 6) It is also interesting that having two connections as in >>> 5) causes different behavior; that is the boot process goes >>> further to light all four LED's and then freezes. >>> >>> Could someone check to see if they are getting similar >>> behavior; I can't imagine that I am doing something real >>> stupid with only a single wire connection; but I have >>> previously done many rather stupid things so you never know >>> (without verification). >>> >>> Would someone in the expert category have some suggestions >>> how to get around this problem; if we can't find a work >>> around, months and months of work will be thrown away. For >>> example, if we configured the device tree that is loaded at >>> boot up, would it take precedence before the default pin mux >>> that causes the freeze (if this happens to be the problem, >>> currently we have no insight into what is causing this behavior). >>> >>> Has anyone else seen similar problems (we may also have >>> something funny with connections to P8-45 and P8-46 but have >>> not tracked this down yet to simple scenarios. >>> >>> I'm open to suggestions as we are currently stuck. Thanks. >>> -- >>> 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. >> >> -- >> 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. >> >> >> >> >> -- >> Gerald >> [email protected] <mailto:[email protected]> >> http://beagleboard.org/ >> http://circuitco.com/support/ >> -- >> For more options, visit http://beagleboard.org/discuss >> --- >> You received this message because you are subscribed to a topic in the >> Google Groups "BeagleBoard" group. >> To unsubscribe from this topic, visit >> https://groups.google.com/d/topic/beagleboard/kMTzEq_A_AY/unsubscribe. >> To unsubscribe from this group and all its topics, 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.
