U-Boot. Where does it all begin?

Question

Newbie question here.

I'm looking at a u-boot boardfile, and it has many functions in it.
For example; board_mmc_init(), enet_board_init(), setup_splash_img(), etc.

Most of these functions don't get called from within the boardfile. They get called from somewhere else. But I can't figure out where.

In Linux kernel boardfiles there's a machine structure. In there we might have .init_machine = myboard_init. Then myboard_init(void) will call other functions which will in turn call other functions. I find this style easy to read.

My question is; does u-boot have an equivalent of .init_machine? Where do I look to see where everything 'starts'? Who calls all those loose functions thrown together inside a u-boot boardfile?

Answer 1

First of first, uboot will start at start.S of the specify CPU, like this: http://git.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=blob;f=arch/arm/cpu/armv7/start.S;h=ef62fc83270a327bc7df970f598540f1d7ce0fe2;hb=HEAD

It will do some stuff like "exception vector" setup, cache setup, etc.

Then it will jump to http://git.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=blob;f=arch/arm/lib/crt0.S do some c runtime setup,

Then it will back to start.S, after some misc stuff, you can refer the comments, it will jump into lowlevel_init.S http://git.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=blob;f=arch/arm/cpu/armv7/lowlevel_init.S;h=82b2b86520eb2b2d63c2478145b625a49f931542;hb=HEAD

Then.. it will going to soc(very common in ARM) init, like this: http://git.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=blob;f=arch/arm/cpu/armv7/mx6/soc.c

After soc init finish , it will going to some board relate init, in the board init, it will call some periphery device/driver init.

Hope that will give your some hit on uboot process.

Answer 2

I have an raspberry pi board which comes with bcm283x broadcom architecture and arm1176 arm core. So start.S is located in arch/arm/cpu/arm1176/start.S. This will initializes critical registers and disables mmu. Next it will do lowlevel_init and then branch to _main which is defined in case of raspberry pi is in arch/arm/lib/crt0.S This initializes stack pointer and global data and calls board_init_f to initialize the system RAM(DRAM) for executing u-boot code. It should use global_data pointer to execute.

Answer 3

On u-boot-2013.04, board_mmc_init gets called from drivers/mmc/mmc.c, function mmc_initialize(...).

To find this, "grep -r" (recursive) is your friend.

"Where do I look to see where everything 'starts' ?"

Not sure, but look for ENTRY(_start) lines.