[U-Boot] ARMv7 Execution Flow
Hi,
I'm a new U-Boot user. I'm trying to follow the flow of execution for the ARMv7 architecture, and have found myself running into confusion.
At the end of arch/arm/cpu/armv7/start.S, lowlevel_init is called. This is defined (for the ARMv7 architecture in arch/arm/cpu/armv7/low_level_init.S (not sure if there's a reason for the discrepancy in the use of underscores?), and at the end of this file, s_init is called.
As far as I can tell, s_init is only defined for some of the ARMv7 CPUs: the bcm281xx folder doesn't contain any files that define this function. In the case of the am33xx CPU it's defined in board.c, but this function seems to return without calling board_init_f.
My questions are:
1. In the case of the bcm281xx, what happens? s_init doesn't seem to be defined for this CPU. 2. In the case of the am33xx, where is board_init_f called? As far as I can tell, s_init should return to lowlevel_init without having called board_init_f , which then returns back to start.S, terminating the execution prematurely.
I presume my analysis of the assembly must be highly incorrect?
Sorry if this is the wrong place for such a question.
Yours,
James Pollard
Hi James,
On Saturday 04 June 2016 12:25 AM, James Pollard wrote:
Hi,
I'm a new U-Boot user. I'm trying to follow the flow of execution for the ARMv7 architecture, and have found myself running into confusion.
At the end of arch/arm/cpu/armv7/start.S, lowlevel_init is called. This is defined (for the ARMv7 architecture in arch/arm/cpu/armv7/low_level_init.S (not sure if there's a reason for the discrepancy in the use of underscores?), and at the end of this file, s_init is called.
So, s_init is called by cpu_init_crit and after that _main will be called. Below is the code flow for u-boot(Skipped all the #ifdefs).
- reset - save_boot_params - cpu_init_cp15: - Invalidate caches and apply erratas: - cpu_init_crit: - lowlevel_init - s_init - _main (arch/arm/lib/crt0.S) - Setup C runtime environment - board_init_f - relocate code if !SPL - board_init_r
As far as I can tell, s_init is only defined for some of the ARMv7 CPUs: the bcm281xx folder doesn't contain any files that define this function. In the case of the am33xx CPU it's defined in board.c, but this function seems to return without calling board_init_f.
s_init is not necessary to be called for all the boards. board_init_f should take care of system init. As per the above code flow board_init_f will be called for every board.
My questions are:
- In the case of the bcm281xx, what happens? s_init doesn't seem to be
defined for this CPU.
Yes, board_init_f will take care of the initialization.
- In the case of the am33xx, where is board_init_f called? As far as I
can tell, s_init should return to lowlevel_init without having called board_init_f , which then returns back to start.S, terminating the execution prematurely.
This has been answered above.
I presume my analysis of the assembly must be highly incorrect?
Sorry if this is the wrong place for such a question.
Yes, this is the right place to ask :)
Thanks and regards, Lokesh
Yours,
James Pollard _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
Hi James,
On 06/05/2016 08:48 PM, Lokesh Vutla wrote:
Hi James,
On Saturday 04 June 2016 12:25 AM, James Pollard wrote:
Hi,
I'm a new U-Boot user. I'm trying to follow the flow of execution for the ARMv7 architecture, and have found myself running into confusion.
...
I've found, in my similar explorations for other architectures, that the link map can provide clues to where a particular function is linked from.
In this case, based on the reply from Lokesh, I'd imagine the link map would show no definition. Also, perhaps there is an objdump option to display this info.
I've noticed however, since the change to Kbuild, the names of all files contributing to the final link are "build-in.o" which decreases the usefulness of the link map for this purpose.
Jim
Hi James,
On 6 June 2016 at 07:38, James Chargin jimccrown@gmail.com wrote:
Hi James,
On 06/05/2016 08:48 PM, Lokesh Vutla wrote:
Hi James,
On Saturday 04 June 2016 12:25 AM, James Pollard wrote:
Hi,
I'm a new U-Boot user. I'm trying to follow the flow of execution for the ARMv7 architecture, and have found myself running into confusion.
...
I've found, in my similar explorations for other architectures, that the link map can provide clues to where a particular function is linked from.
In this case, based on the reply from Lokesh, I'd imagine the link map would show no definition. Also, perhaps there is an objdump option to display this info.
I've noticed however, since the change to Kbuild, the names of all files contributing to the final link are "build-in.o" which decreases the usefulness of the link map for this purpose.
You can also take a look at the README under 'Board Initialisation Flow:'. Unfortunately not all boards use this new flow, but it should at least provide you with the intent. This is indeed an area that takes some time to understand.
Regards, Simon
participants (4)
-
James Chargin -
James Pollard -
Lokesh Vutla -
Simon Glass