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I have a system that booted into Linux using UBOOT. I can see that it is booting when I connect to it via serial port. How can I stop it booting UBOOT and get the UBOOT command prompt?
During boot, I can see the following messages on attached serial terminal:
Security Framework initialized
Mount-cache hash table entries: 512
CPU: Testing write buffer coherency: ok
devtmpfs: initialized
TI81XX: Map 0xb3200000 to 0xfe500000 for dram barrier
TI81XX: Map 0x40300000 to 0xfe600000 for sram barrier
omap_voltage_early_init: voltage driver support not added
regulator: core version 0.5
regulator: dummy:
NET: Registered protocol family 16
omap_voltage_domain_lookup: Voltage driver init not yet happened.Faulting!
omap_voltage_add_dev: VDD specified does not exist!
OMAP GPIO hardware version 0.1
OMAP GPIO hardware version 0.1
OMAP GPIO hardware version 0.1
OMAP GPIO hardware version 0.1
Cannot clk_get ck_32
.....
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Once you can read the output from your host machine, the U-Boot Console can be easily accessed by pressing any button before the autoboot sequence starts. By default, U-Boot waits up to 3 seconds before starting the autoboot sequence.
Running "run bootcmd" will load your kernel, dtb etc if you stop normal boot. The "=>" signalls, that you are in the U-Boot shell. It is the default prompt string. To change the prompt string, you must modify the CONFIG_SYS_PROMPT parameter and recompile.
Do you mean the command of uboot to reboot the board? If yes, you can use "reset" command in uboot to reboot system, the eventual operation of "reset" command will trigger a wdog reset which will reboot i.
Normally, u-boot can be interrupted by hitting Escape on serial console during boot.
But, it really depends on how u-boot was configured by OEM. Also, keep in mind that there is no such thing as single coherent u-boot - it has at least 40 semi-official forks and god knows how many unofficial ones. It is possible to configure u-boot such that you cannot really interrupt boot process, but it is not very common.
If that does not work, if could be that your serial terminal program is not configured to the same settings as was provisioned by OEM - speed, parity, flow control, etc. I would suggest trying to change terminal program serial speed from 115200 bps (most common) all way down to 9600 (not common, but possible), and changing flow control to None, Xon/Xoff, CTS/RTS. If nothing works, you may want to use another serial cable - some systems may require NULL-modem cable. Good luck!
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