1 RAMBOOT for MPC85xx Platforms 2 ============================== 3 4RAMBOOT literally means boot from DDR. But since DDR is volatile memory some 5pre-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 7 itself. 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. 10 11In addition to the above there could be some more methods to initialize the DDR 12and load it manually. 13Two of them are described below.There is also an explanation as to where these 14methods could be handy. 151. Load the RAM based bootloader onto DDR via JTAG/BDI interface. And then 16 execute the bootloader from DDR. 17 This may be handy in the following cases: 18 - In very early stage of platform bringup where other boot options are not 19 functional because of various reasons. 20 - In case the support to program the flashes on the board is not available. 21 222. Load the RAM based bootloader onto DDR using already existing bootloader on 23 the board.And then execute the bootloader from DDR. 24 Some usecases where this may be used: 25 - While developing some new feature of u-boot, for example USB driver or 26 SPI driver. 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 32 support for example AMP boot. In this case also RAM boot loader can be 33 utilized. 34 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. 37 38Both the above Bootloaders are slight variants of SDcard or SPI Flash 39bootloader or for that matter even NAND bootloader. 40All of them define CONFIG_SYS_RAMBOOT. 41The main difference among all of them is the way the pre-environment is getting 42configured and who is doing that. 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 bootloader. 46 47How to use them: 481. Using JTAG 49 Boot up in core hold off mode or stop the core after reset using JTAG 50 interface. 51 Preconfigure DDR/L2SRAM through JTAG interface. 52 - setup DDR controller registers. 53 - setup DDR LAWs 54 - setup DDR TLB 55 Load the RAM based boot loader to the proper location in DDR/L2SRAM. 56 set up IAR (Instruction counter properly) 57 Enable the core to execute. 58 592. Using already existing bootloader. 60 get the rambased boot loader binary into DDR/L2SRAM via tftp. 61 execute the RAM based bootloader. 62 => tftp 11000000 u-boot-ram.bin 63 => go 1107f000 64 65Please note that L2SRAM can also be used instead of DDR if the SOC has 66sufficient size of L2SRAM. 67 68Necessary Code changes Required: 69===================================== 70Please note that below mentioned changes are for 85xx platforms. 71They have been tested on P1020/P2020/P1010 RDB. 72 73The main difference between the above two methods from technical perspective is 74that in 1st case SOC is just out of reset so it is in default configuration. 75(CCSRBAR is at 0xff700000). 76In the 2nd case bootloader has already re-located CCSRBAR to 0xffe00000 77 781. File name-> boards.cfg 79 There can be added specific Make options for RAMBoot. We can keep different 80 options for the two cases mentioned above. 81 for example 82 P1020RDB_JTAG_RAMBOOT and P1020RDB_GO_RAMBOOT. 83 842. platform config file 85 for example include/configs/P1_P2_RDB.h 86 87 #ifdef CONFIG_RAMBOOT 88 #define CONFIG_SDCARD 89 #endif 90 91 This will finally use the CONFIG_SYS_RAMBOOT. 92 933. File name-> arch/powerpc/include/asm/config_mpc85xx.h 94 In the section of the particular SOC, for example P1020, 95 96 #if defined(CONFIG_GO) 97 #define CONFIG_SYS_CCSRBAR_DEFAULT 0xffe00000 98 #else 99 #define CONFIG_SYS_CCSRBAR_DEFAULT 0xff700000 100 #endif 101 102For JTAG RAMBOOT this is not required because CCSRBAR is at ff700000. 103