What is the purpose of U-Boot?
U-Boot boots an operating system by reading the kernel and any other required data (e.g. device tree or ramdisk image) into memory, and then executing the kernel with the appropriate arguments. U-Boot’s commands are actually generalized commands which can be used to read or write any arbitrary data.
How do I stop U-Boot?
1 Answer. Normally, u-boot can be interrupted by hitting Escape on serial console during boot.
Why does U-Boot relocate itself?
U-Boot relocates itself for a variety of reasons – initially the SDRAM may not have been set up and U-Boot is running from SRAM or a ROM. This would also require updates to the firmware such that it copies and jumps to U-Boot at the right address.
What is Bootcmd?
bootcmd : This variable defines a command string that is automatically executed when the initial countdown is not interrupted. This command is only executed when the variable bootdelay is also defined!
What does the U mean in BIOS?
BIOS is essentially a PC concept, having appeared in CP/M personal computers and the original IBM PC. U-Boot tries to live up to its name (“Universal Boot”), and has been ported to many architectures/platforms.
How configure U-Boot?
To summarize, you need to configure U-Boot for your with the following steps:
- Add your board device tree: arch/arm/dts/.
- Create your own board support directory: board//.
- Add TARGET_ _ in Kconfig.
- Create your board defconfig: defconfig/_defconfig.
How do I get to U-Boot?
Booting into U-Boot
- Log in to your switch via the console.
- Reboot the switch: cumulus@switch~:$ sudo reboot.
- Press any key when you see the following prompt: Hit any key to stop autoboot: 0 The full output from the boot sequence is in this file: reboot.txt.
- The switch will now boot into U-Boot.
Where are U-Boot environment variables stored?
SD Card memory
The U-Boot environment is stored in the SD Card memory and is persistent across power or reset cycles. Parameters defined by the U-boot environment variables include: target IP address, target MAC address, location in RAM where a Linux bootable image will be loaded, and many others.
What is Bootargs in U-Boot?
When combined with a U-Boot variable named bootargs, this feature allows you to tell the kernel how to configure various device drivers, where to find the root filesystem and can even be used to pass information to applications on the system. …
How do I stop Autoboot U-Boot?
To stop the automatic booting (autoboot) of the pre-installed kernel, send a character to the serial port by pressing a key from the serial console connected to the target. If U-Boot is stopped, it displays a command line console (also called monitor).
Why is UEFI preferable to BIOS?
UEFI provides faster boot time. UEFI has discrete driver support, while BIOS has drive support stored in its ROM, so updating BIOS firmware is a bit difficult. UEFI offers security like “Secure Boot”, which prevents the computer from booting from unauthorized/unsigned applications.
How is U-Boot strict in its argument parsing?
U-Boot is strict in its argument parsing. It expects most values to be provided in hexadecimal form. In the case of the cp command, for example, this means that the source address, the target address, and the byte count must be provided in hexadecimal values.
Where is the U-Boot variable in FAT boot?
The bootargs U-Boot environment variable (if it exists) is passed to the kernel as boot arguments and will override the bootargs property of the chosen node in the device tree. The bootargs variable is set in the uEnv.txt file located in the FAT boot partition of the standard snickerdoodle SD card image.
What happens when you do not press a key in U-Boot?
If you do not press a key during those five seconds, U-Boot boots its default configuration. By pressing a key, you get a prompt: One of the first things you probably want to try is obtaining help from U-Boot: As you can see, U-Boot has a lot of commands. Fortunately, U-Boot also provides per-command help:
Which is an example of an U-boot environment?
Example U-Boot environment, as found in uEnv.txt from a stock android U-Boot environment partition Recent version of U-Boot are able to boot from NFS as well as TFTP, but you have to get rid of the automatic setup of FTP. Check Ethernet for more information.