[U-Boot] Code Structure and API functionality of U-Boot

Hi,  I am a new member to u-boot mail list.   I have the source code of u-boot downloaded.I am aware that /boot,/board,/driver,include/config are the directory of imprtance.   I am trying to read the code.   1.I see that there are lots of other files and lots of APIs in the above direcories.Can some one  describe/explain which API,which file does what operation say for ARM boards.   Any document/book suggestion on U-BOOT will be also helpfull on understanding the API functionality.   2.Suppose I want to debug the U-Boot code.Should I use Abatron BDI2000 hardware debugger ? OR is there any other method available?(I suppose I can not use gdb/kgdb)   Regards Chandan