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.
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[email protected] <mailto:[email protected]>
http://beagleboard.org/
http://circuitco.com/support/
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