SYS_BOOT2 is present on P8-43. I would try to place a resistor between this point and ground first. The Pull-up is pretty weak (100kOhm), so something like 10 k would probably do the job. Off course this pin is also used as LCD_DATA2, but if you can live with it, it is a lot better than moving R93-R68 on the board
On Wednesday, May 21, 2014 7:34:34 PM UTC+2, john3909 wrote: > > > From: Alberto Potenza <alberto....@gmail.com <javascript:>> > Reply-To: <beagl...@googlegroups.com <javascript:>> > Date: Wednesday, May 21, 2014 at 3:00 AM > To: <beagl...@googlegroups.com <javascript:>> > Subject: [beagleboard] Bootloader, MLO, u-boot and boot button > > Dear all, > I have some problems trying to understand how the boot procedure is in the > Beaglebone Black. > I saw several posts around but it is quite hard for me to fully understand > how it works. So, sorry if I am repeating something that most of you > already know. > What I've understood so far (I hope...) is: > 1) if I just power my BBB, the boot procedure is based on the flash placed > on the BBB. It means that the ROM Bootloader of the AM335xx loads the MLO > from the flash, the u-boot.img from the flash and then "all the rest" > starts. > 2) if I power my BBB and I push the Boot-button, the ROM Bootloader of the > AM335xx loads the MLO and the u-boot.img and "all the rest" from the SD > card. The AM335xx does not talk at all with the flash during all the boot > procedure. > 3) if I try to modify the uEnv.txt in the SD card in such a way to force > the OS to be loaded form the SD card, wich means > > mmc dev 1 > mmc rstn 1 > gpio set 52 > optargs=capemgr.disable_partno=BB-BONELT-HDMI,BB-BONELT-HDMIN,BB-BONE-EMMC-2G > etc..etc > > and I do not push the boot button, the AM335xx loads the MLO and the > u-boot.img from the flash and "only after that" it will loads the uEnv.txt > file from the SD card. It means that the bootloader will search a MLO and > u-boot.img in the flash -> they will talk for a while and after that the > AM335xx will loads the uEnv.txt from the SD. > > Now, I would like to have the point number two without to push the boot > button: I do not want the AM335xx to talk with the flash at all and I am > not pretty sure it is possible. In my opinion there are two ways: > the former is to set the resistor on the BBB in such a way to have the > same configuration as the boot-button pressed (hardware way). The latter is > to erase completely the flash in such a way to have no MLO and u-boot.img > in it. However, the second way could not work because the AM335xx will talk > with the flash trying to find MLO and the u-boot.img, while I do not want > them to talk each other. > > Is it all correct? > > Your understanding is correct. The bootloader looks for MLO with a > specific header on the eMMC and if it does not find one, it looks for an > MLO on the SDCard. If you look at sheet 6 in the BBB schematics, there is a > table which shows the boot order given the SYSBOOT settings. If you don’t > want the BBB to access the eMMC at boot time, you must move resistors on > the board as you indicated. > > Regards, > John > > > > Thanks a lot. > > Alberto > > -- > 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...@googlegroups.com <javascript:>. > 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 beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
