am335x_evm: Add basic README
Add a README for the family of boards the am335x_evm covers, and include instructions on preparing and using falcon mode, for various media. Signed-off-by: Tom Rini <trini@ti.com> Reviewed-by: Peter Korsgaard <jacmet@sunsite.dk> Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
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Tom Rini
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board/ti/am335x/README
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board/ti/am335x/README
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Summary
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=======
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This document covers various features of the 'am335x_evm' build, and some of
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the related build targets (am335x_evm_uartN, etc).
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Hardware
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========
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The binary produced by this board supports, based on parsing of the EEPROM
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documented in TI's reference designs:
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- AM335x GP EVM
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- AM335x EVM SK
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- Beaglebone White
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- Beaglebone Black
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Falcon Mode
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===========
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The default build includes "Falcon Mode" (see doc/README.falcon) via NAND,
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eMMC (or raw SD cards) and FAT SD cards. Our default behavior currently is
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to read a 'c' on the console while in SPL at any point prior to loading the
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OS payload (so as soon as possible) to opt to booting full U-Boot. Also
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note that while one can program Falcon Mode "in place" great care needs to
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be taken by the user to not 'brick' their setup. As these are all eval
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boards with multiple boot methods, recovery should not be an issue in this
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worst-case however.
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Falcon Mode: eMMC
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=================
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The recommended layout in this case is:
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MMC BLOCKS |--------------------------------| LOCATION IN BYTES
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0x0000 - 0x007F : MBR or GPT table : 0x000000 - 0x020000
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0x0080 - 0x00FF : ARGS or FDT file : 0x010000 - 0x020000
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0x0100 - 0x01FF : SPL.backup1 (first copy used) : 0x020000 - 0x040000
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0x0200 - 0x02FF : SPL.backup2 (second copy used) : 0x040000 - 0x060000
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0x0300 - 0x06FF : U-Boot : 0x060000 - 0x0e0000
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0x0700 - 0x08FF : U-Boot Env + Redundant : 0x0e0000 - 0x120000
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0x0900 - 0x28FF : Kernel : 0x120000 - 0x520000
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Note that when we run 'spl export' it will prepare to boot the kernel.
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This includes relocation of the uImage from where we loaded it to the entry
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point defined in the header. As these locations overlap by default, it
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would leave us with an image that if written to MMC will not boot, so
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instead of using the loadaddr variable we use 0x81000000 in the following
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example. In this example we are loading from the network, for simplicity,
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and assume a valid partition table already exists and 'mmc dev' has already
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been run to select the correct device. Also note that if you previously
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had a FAT partition (such as on a Beaglebone Black) it is not enough to
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write garbage into the area, you must delete it from the partition table
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first.
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# Ensure we are able to talk with this mmc device
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U-Boot # mmc rescan
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U-Boot # tftp 81000000 am335x/MLO
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# Write to two of the backup locations ROM uses
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U-Boot # mmc write 81000000 100 100
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U-Boot # mmc write 81000000 200 100
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# Write U-Boot to the location set in the config
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U-Boot # tftp 81000000 am335x/u-boot.img
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U-Boot # mmc write 81000000 300 400
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# Load kernel and device tree into memory, perform export
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U-Boot # tftp 81000000 am335x/uImage
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U-Boot # run findfdt
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U-Boot # tftp ${fdtaddr} am335x/${fdtfile}
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U-Boot # run mmcargs
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U-Boot # spl export fdt 81000000 - ${fdtaddr}
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# Write the updated device tree to MMC
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U-Boot # mmc write ${fdtaddr} 80 80
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# Write the uImage to MMC
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U-Boot # mmc write 81000000 900 2000
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Falcon Mode: FAT SD cards
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=========================
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In this case the additional file is written to the filesystem. In this
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example we assume that the uImage and device tree to be used are already on
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the FAT filesystem (only the uImage MUST be for this to function
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afterwards) along with a Falcon Mode aware MLO and the FAT partition has
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already been created and marked bootable:
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U-Boot # mmc rescan
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# Load kernel and device tree into memory, perform export
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U-Boot # load mmc 0:1 ${loadaddr} uImage
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U-Boot # run findfdt
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U-Boot # load mmc 0:1 ${fdtaddr} ${fdtfile}
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U-Boot # run mmcargs
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U-Boot # spl export fdt ${loadaddr} - ${fdtaddr}
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This will print a number of lines and then end with something like:
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Using Device Tree in place at 80f80000, end 80f85928
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Using Device Tree in place at 80f80000, end 80f88928
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So then you:
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U-Boot # fatwrite mmc 0:1 0x80f80000 args 8928
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Falcon Mode: NAND
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=================
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In this case the additional data is written to another partition of the
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NAND. In this example we assume that the uImage and device tree to be are
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already located on the NAND somewhere (such as fileystem or mtd partition)
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along with a Falcon Mode aware MLO written to the correct locations for
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booting and mtdparts have been configured correctly for the board:
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U-Boot # nand read ${loadaddr} kernel
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U-Boot # load nand rootfs ${fdtaddr} /boot/am335x-evm.dtb
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U-Boot # run nandargs
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U-Boot # spl export fdt ${loadaddr} - ${fdtaddr}
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U-Boot # nand erase.part u-boot-spl-os
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U-Boot # nand write ${fdtaddr} u-boot-spl-os
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