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| -rw-r--r-- | doc/README.ramboot-ppc85xx | 102 |
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diff --git a/doc/README.ramboot-ppc85xx b/doc/README.ramboot-ppc85xx new file mode 100644 index 0000000000..8ed45fb46d --- /dev/null +++ b/doc/README.ramboot-ppc85xx @@ -0,0 +1,102 @@ + RAMBOOT for MPC85xx Platforms + ============================== + +RAMBOOT literally means boot from DDR. But since DDR is volatile memory some +pre-mechanism is required to load the DDR with the bootloader binary. +- In case of SD and SPI boot this is done by BootROM code inside the chip + itself. +- In case of NAND boot FCM supports loading initial 4K code from NAND flash + which can initialize the DDR and get the complete bootloader copied to DDR. + +In addition to the above there could be some more methods to initialize the DDR +and load it manually. +Two of them are described below.There is also an explanation as to where these +methods could be handy. +1. Load the RAM based bootloader onto DDR via JTAG/BDI interface. And then + execute the bootloader from DDR. + This may be handy in the following cases: + - In very early stage of platform bringup where other boot options are not + functional because of various reasons. + - In case the support to program the flashes on the board is not available. + +2. Load the RAM based bootloader onto DDR using already existing bootloader on + the board.And then execute the bootloader from DDR. + Some usecases where this may be used: + - While developing some new feature of u-boot, for example USB driver or + SPI driver. + Suppose the board already has a working bootloader on it. And you would + prefer to keep it intact, at the same time want to test your bootloader. + In this case you can get your test bootloader binary into DDR via tftp + for example. Then execute the test bootloader. + - Suppose a platform already has a propreitery bootloader which does not + support for example AMP boot. In this case also RAM boot loader can be + utilized. + + So basically when the original bootloader is required to be kept intact + RAM based bootloader can offer an updated bootloader on the system. + +Both the above Bootloaders are slight variants of SDcard or SPI Flash +bootloader or for that matter even NAND bootloader. +All of them define CONFIG_SYS_RAMBOOT. +The main difference among all of them is the way the pre-environment is getting +configured and who is doing that. +- In case of SD card and SPI flash bootloader this is done by On Chip BootROM inside the Si itself. +- In case of NAND boot SPL/TPL code does it with some support from Si itself. +- In case of the pure RAM based bootloaders we have to do it by JTAG manually or already existing bootloader. + +How to use them: +1. Using JTAG + Boot up in core hold off mode or stop the core after reset using JTAG + interface. + Preconfigure DDR/L2SRAM through JTAG interface. + - setup DDR controller registers. + - setup DDR LAWs + - setup DDR TLB + Load the RAM based boot loader to the proper location in DDR/L2SRAM. + set up IAR (Instruction counter properly) + Enable the core to execute. + +2. Using already existing bootloader. + get the rambased boot loader binary into DDR/L2SRAM via tftp. + execute the RAM based bootloader. + => tftp 11000000 u-boot-ram.bin + => go 1107f000 + +Please note that L2SRAM can also be used instead of DDR if the SOC has +sufficient size of L2SRAM. + +Necessary Code changes Required: +===================================== +Please note that below mentioned changes are for 85xx platforms. +They have been tested on P1020/P2020/P1010 RDB. + +The main difference between the above two methods from technical perspective is +that in 1st case SOC is just out of reset so it is in default configuration. +(CCSRBAR is at 0xff700000). +In the 2nd case bootloader has already re-located CCSRBAR to 0xffe00000 + +1. File name-> boards.cfg + There can be added specific Make options for RAMBoot. We can keep different + options for the two cases mentioned above. + for example + P1020RDB_JTAG_RAMBOOT and P1020RDB_GO_RAMBOOT. + +2. platform config file + for example include/configs/P1_P2_RDB.h + + #ifdef CONFIG_RAMBOOT + #define CONFIG_SDCARD + #endif + + This will finally use the CONFIG_SYS_RAMBOOT. + +3. File name-> arch/powerpc/include/asm/config_mpc85xx.h + In the section of the particular SOC, for example P1020, + + #if defined(CONFIG_GO) + #define CONFIG_SYS_CCSRBAR_DEFAULT 0xffe00000 + #else + #define CONFIG_SYS_CCSRBAR_DEFAULT 0xff700000 + #endif + +For JTAG RAMBOOT this is not required because CCSRBAR is at ff700000. |