Yes, I was as well. They are separate issues. This is where the reset comes in for sure. Hold off driving these pins or adding a load to the pins until after RESET goes high. This insures that they are not driven or loaded during the period in which they are being read by the processor to determine the boot mode.
On Fri, Oct 17, 2014 at 3:50 PM, Britton Kerin <[email protected]> wrote: > On Thu, Oct 16, 2014 at 12:25 PM, Robert Nelson <[email protected]> > wrote: > > On Thu, Oct 16, 2014 at 3:17 PM, Britton Kerin <[email protected]> > wrote: > >> The SRM contains the following conflicting information: > >> > >> The System Reference Manual (SRM) says you're supposed to gate all GPIO > >> (and other inputs) such that they aren't driven until either the > SYS_RESET > >> line goes high (according to SRM section 7.1, 8.0, and possibly others) > or > >> until the VDD_3V3B rail is up (according to SRM 8.6.2). Are these > conditions > >> identical in practice? If not which is the right one? > >> > >> Also, the reference manual section 8.3.1 says this: > >> > >> 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. > >> > >> while not wrong this paragraph is going to create a dangerous wrong > impression > >> for most readers: that the boot pins are special and are the ones you > have to > >> worry about driving early. I think it would be good to change this > paragraph > >> or add a pointer to the other warnings that apply to all pins or > something. > > > > Those pins control the bootrom's boot selection. If you drive them the > > wrong way after sys_reset you can change the processor to boot from an > > interface that isn't enable/setup/etc... > > Ah, I understand. They can't be driven during boot. I was stuck on > the power issue. > It might be good to change section 8.3.1 to this: > > If you plan to use any of these signals, then during boot, 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. > > "on power-up" changes to "during boot" or something. > > Britton > > -- > 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]. For more options, visit https://groups.google.com/d/optout.
