U-Boot - Behaviour of 'go' command
I have written a minimal bare-metal Raspberry Pi-3B program (ARM64- CortexA53) to switch from EL2 (Exception Level 2) to EL1. U-Boot is used as the bootloader. The code is loaded to RAM using the "tftpboot" command. The "go" command is used to start the execution of my program. I am not expecting to return the control back to U-Boot.
When the code switches to EL1 using "ERET" instruction the RAM (the jump location) contains the random data. When I inspect (using JTAG) the RAM (again the jump location) just before the ERET I can see the valid program there.
May I know the reason for this behavior? Is there a better alternative to the "go" command?
Thanks a lot, Little
Hi Little,
On Sun, 7 May 2023 at 04:48, Little Tree littletreetrunk32@gmail.com wrote:
I have written a minimal bare-metal Raspberry Pi-3B program (ARM64- CortexA53) to switch from EL2 (Exception Level 2) to EL1. U-Boot is used as the bootloader. The code is loaded to RAM using the "tftpboot" command. The "go" command is used to start the execution of my program. I am not expecting to return the control back to U-Boot.
When the code switches to EL1 using "ERET" instruction the RAM (the jump location) contains the random data. When I inspect (using JTAG) the RAM (again the jump location) just before the ERET I can see the valid program there.
May I know the reason for this behavior? Is there a better alternative to the "go" command?
It could be that the memory becomes inaccessible, but I don't know much about this. You can look at the implementation of the 'go' command in cmd/boot.c but basically it just jumps directly to the code you give it. I am really not sure why it would suddenly vanish due to that.
Regards, SImon
participants (2)
-
Little Tree -
Simon Glass