The card would contain two partitions, a FAT32 partition and Linux ext3/4. Alternatively, if using eMMC, the bootloader can be loaded using RAW mode.Įarly BeagleBone Black images included MLO (and u-boot.img) on a FAT file-system in the root directory of the active primary partition.
#U boot for beaglebone black 32 bit
The ROM code will try to load and execute the first stage bootloader called "MLO" (U-Boot SPL) from a Fat 12/16 or 32 bit MBR based filesystem.
This allows the BeagleBone Black to bypass the onboard eMMC and boot from the removable uSD (provided no valid boot device is found on SPI0.) This can be used to recover from a corrupted onboard eMMC/U-Boot. If the boot switch (S2) is held down during power-up, the ROM will boot from the SPI0 Interface first, followed by MMC0 (external uSD), USB0 and UART0. For this reason, a cut down version of U-Boot called U-Boot SPL (Second Program Loader) is loaded first, and once it has initialised the CPU, it chain loads a fully featured version of U-Boot (u-boot.img).īy default, the ROM code in the Sitara AM3359 will boot from the MMC1 interface first (the onboard eMMC), followed by MMC0 (external uSD), UART0 and USB0. The internal RAM on the AM335X is 128KB, but due to various limitations, only 109KB is available for the initial bootloader for program memory, heap and stack.Ī fully featured version of U-Boot can be over 400KB, hence it is not possible to load this immediately. On reset, this ROM code searches for the bootloader and then copies it to the internal RAM before executing it. The AM335X contains ROM code that can load a bootloader from external memory such as the on-board eMMC.
1.2 Testing the fully featured second stage U-Boot Bootloader.1.1 Compiling U-Boot for the BeagleBone Black.
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