u-boot/doc/README.ramboot-ppc85xx

5 pre-mechanism is required to load the DDR with the bootloader binary.
6 - In case of SD and SPI boot this is done by BootROM code inside the chip
8 - In case of NAND boot FCM supports loading initial 4K code from NAND flash
9   which can initialize the DDR and get the complete bootloader copied to DDR.
15 1. Load the RAM based bootloader onto DDR via JTAG/BDI interface. And then
16    execute the bootloader from DDR.
18      - In very early stage of platform bringup where other boot options are not
20      - In case the support to program the flashes on the board is not available.
22 2. Load the RAM based bootloader onto DDR using already existing bootloader on
23    the board.And then execute the bootloader from DDR.
25       - While developing some new feature of u-boot, for example USB driver or
27 	Suppose the board already has a working bootloader on it. And you would
28 	prefer to keep it intact, at the same time want to test your bootloader.
29 	In this case you can get your test bootloader binary into DDR via tftp
30 	for example. Then execute the test bootloader.
31      - Suppose a platform already has a propreitery bootloader which does not
35    So basically when the original bootloader is required to be kept intact
36    RAM based bootloader can offer an updated bootloader on the system.
39 bootloader or for that matter even NAND bootloader.
41 The main difference among all of them is the way the pre-environment is getting
43 - In case of SD card and SPI flash bootloader this is done by On Chip BootROM inside the Si itself.
44 - In case of NAND boot SPL/TPL code does it with some support from Si itself.
45 - In case of the pure RAM based bootloaders we have to do it by JTAG manually or already existing b…
49    Boot up in core hold off mode or stop the core after reset using JTAG
52 	- setup DDR controller registers.
53 	- setup DDR LAWs
54 	- setup DDR TLB
59 2. Using already existing bootloader.
61    execute the RAM based bootloader.
62       => tftp 11000000 u-boot-ram.bin
76 In the 2nd case bootloader has already re-located CCSRBAR to 0xffe00000
78 1. File name-> boards.cfg