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Debugging MLO with BDI3000 ( am335x- beaglebone black)

Harsha Kiran
Intellectual 545 points

Hi ,

i am trying to understand in detail about the booting process in the beaglebone black. I have a BDI3000 through which i am debugging the MLO on the target using the eclipse IDE.

I could able to trace the Disassembly to the source code till the PLL initialization and the PC is stuck in a dead loop and i cannot progress further.. 

It would be greatfull if anyone can help me understand what exactly is going on with the following questions:

Question1:

I have my eMMC of the BBB loaded with the appropriate image. It can boot the board upon reset.

But i am trying to load the u-boot.spl binary from the SPL folder of the U-boot and load it in the 0x402F0400 address through the configuration file of the BDi3000. I could able to set a break point at 0x402F0400 and see the source code to the disassembly. i am stepping in at every instruction and learning the details of all the files it is using ( lowlevelinit.s, clock_am33xx.c..) ..i could able to set a break point at s_init ( 0x402F19a8) and when i step in the pll_init() from the board.c file ---> void pll_init()---> clocl_am335xx.c

the PC is stuck in the loop and cannot go further..is it the correct way to bebug?? since its the very low level code, is it a good idea to step into every instruction to see what is happening..and why is it getting stuck in the PLL??

Question 2:

This time i am not loading the u-boot-spl ( MLO) from the config file. when i am in debug mode and hit the run button, the PC goes to the RAM address and the board gets booted and running.. instead i put a break point again at 0X402F0400 and stried to stop it.. it stoped and i can again step through all the instructions...This time it is not going into the Board.c file but goes directly to the clock-am33xx.c and stops again at PLL initialization..and i get this error message saying the target memory cannot be accessed.

i am not clear on the exact booting process..i tried to see the u-boot-spl memory map file..i am not able to understand why it has problem with PLL when i try to stop my debugging but the board can boot if i dont stop.. am i missing anything? when does the actual loading of u-boot.img start??

Thanks for your time,

Roy