There are actually more than 3 boots options, and among them are what you covered, plus SPI, Ethernet( TFTP kernel / NFS root ), USB, and I know I am forgetting a couple more.
To keep things in context with what you're asking however. LIke John says uEnv,txt has control over how the device boots. It has a sort of round robin check it does when bringing the hardware up. In the case of the SD card boot, the uEnv.txt file is only going to know about the sd card unless specifically modified to override default behavior. Now what you're talking about seems to be a flasher image type image. Which is to say, it is meant to flash the eMMC back to factory default, or to flash a newer more modern version of Angstrom or whatever image you have. If you want to boot exclusively off of the SD card, then you're going to have to work at it a bit. A jumper switch may seem like a better idea at first ( for boot options ) but it really is not. uboot boot options are vast . . . Anyways, you're going to have to ask yourself how serious you are about getting your device booting exclusively from the SD card. Because if you truly want to understand how it all works, you're going to need to understand uboot, and Linux better than it appears how well you know it now. Also, there are other options to consider. Which Linux distro do you want to use . . . and more questions to be answered yet. In short, you have your work cut out for you if you want to learn. Weeks, and perhaps even months. On Wed, Dec 4, 2013 at 8:43 PM, John Syne <[email protected]> wrote: > > > From: Gerald Coley <[email protected]> > Reply-To: <[email protected]> > Date: Wednesday, December 4, 2013 at 4:55 PM > To: "[email protected]" <[email protected]> > Subject: Re: [beagleboard] How to make BeagleBone black boot off SD card > > Push and hold the boot button and apply power. > > http://www.elinux.org/Beagleboard:BeagleBoneBlack > > Gerald > > Let me clear something up that seems to be confusing everyone. Gerald is > correct from a hardware point of view; however this only selects which > u-boot environment is loaded. When the boot button is pressed, the u-boot > env is loaded from the SDCard and when the boot button isn’t pressed, the > eMMC u-boot env is loaded. From that point onwards the current u-boot env > checks to see if the SDCard is installed and if it is, u-boot boots from > the SDCard FAT partition. If the SDCard isn’t installed, it boots from the > eMMC FAT partition. Since the u-boot env is the same on both the SDCard and > the eMMC, it doesn’t matter if the boot button is pressed or not. It is the > uEnv.txt file that modifies u-boot env behavior by adding a “uenvcmd” line. > > I hope I haven’t confused everyone. > Regards, > John > > > > > On Wed, Dec 4, 2013 at 3:50 PM, <[email protected]> wrote: > >> Good afternoon, >> I don't understand how to determine whether the BBB is booting off the SD >> card or booting off the internal flash. >> Here's what happened, I installed a 4GB image from getting started >> section onto my SD card >> This was the first image here: >> http://beagleboard.org/latest-images >> >> >> Initially I powered on by holding the button next to SD card, It booted >> and I could tell it was not the internal image, because it did not have the >> demo applications. >> >> Next, I tried hitting the reset button to see if it will boot off the SD >> card again, nothing happened and I could not connect to the BBB any more. I >> scanned all ports and it was not available. >> >> I tried resetting and holding down the button again, but it would not >> boot off the SD card. >> >> Only when I take out the SD card the BBB boots into the original >> installation. >> >> Does anyone know what may have caused this? This is a brand new SD card, >> and I doubt I had damaged it by resetting the BBB. >> >> As far as I understand there are 3 booting options, >> >> 1. There is booting off internal NAND which only has 70mb (or is this >> only a partition >> 2. Booting off SD card >> 3. "If using BeagleBone Black and the image is meant to program your >> on-board eMMC, you'll need to wait while the programming occurs. When the >> flashing is complete, all 4 USRx LEDs will be lit solid. *This can >> take up to 45 minutes."* >> >> >> What I don't understand is how to select how the device boots. How can I >> make it boot off the SD card every time? How do I prevent it from writing >> to the NAND? I want to prevent damaging anything by overwriting the NAND >> and only work within an SD Card. >> >> Wouldn't it have been easier to install a jumper to select which memory >> the device boots from? >> >> 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/groups/opt_out. >> > > -- > 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/groups/opt_out. > > -- > 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/groups/opt_out. > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. 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