Repartitioning 4GB Beaglebone Black eMMC flash

Creating kernel.its file

Just use the sample 'kernel_fdt.its', edit and use it. Here is my 'kernel.its' file ,

/dts-v1/;

/ {
        description = "ARM BBLK FIT (Flattened Image Tree)";
        #address-cells = <1>;

        images {
                kernel@1 {
                        description = "ARM BeagleboneBlack Linux-4.1.13";
                        data = /incbin/("zImage");
                        type = "kernel";
                        arch = "arm";
                        os = "linux";
                        compression = "none";
                        load = <0x80008000>;
                        entry = <0x80008000>;
                        hash@1 {
                        algo = "crc32";
                        };
                        hash@2 {
                                algo = "sha1";
                        };
                };

                fdt@1 {
                        description = "ARM Boneblack device tree blob";
                        data = /incbin/("am335x-boneblack.dtb");
                        type = "flat_dt";
                        arch = "arm";
                        compression = "none";

                        hash@1 {
                                algo = "crc32";
                        };
                        hash@2 {
                                algo = "sha1";
                        };
                };

        };

        configurations {
                default = "config@1";

                config@1 {
                        description = "BeagleboneBlack";
                        kernel = "kernel@1";
                        fdt = "fdt@1";
                };

        };
};

Pay attention to 'data' field. If your data file is not in the current directory where the kernel.its file resides you need to adjust their paths accordingly. This is suppposedly the simplest form of 'its' file I need to create FDT image. Next I do,

$mkimage -f kernel.its zImage.itb

The output zImage.itb (I can name it anything) is my FIT file ready to be loaded. I need to do one more thing to complete this process.

Create boot.scr

I notice that every time I boot, I see this message on the console port,

SD/MMC found on device 1
reading boot.scr
** Unable to read file boot.scr **
reading uEnv.txt

This is because there was no boot.scr so u-boot falls back to reading uEnv.txt instead. 'boot.scr' is not text file, but an image file. This is the source file for my boot.scr. Basically I can convert uEnv.txt to boot.scr, but I want a much simpler one. This is my 'boot.scr.src',

set loadaddr 82000000
set bootargs 'console=ttyS0,115200n8 rootfstype=ext4 root=/dev/mmcblk0p2 earlyprintk'
fatload mmc 1:1 $loadaddr zImage.itb
bootm $loadaddr

This is it for now. It is the minimalist approach. Next I create 'boot.scr',

$mkimage  -C none -A arm -T script -a 80000000 -e 80000000 -d boot.scr.src boot.scr

This is my default boot.scr that is copied to the boot partition (FAT) of the flash MMC1 where u-boot will read from at boot time. Here is what happens after all these things,

Scanning mmc 1:1...
Found U-Boot script /boot.scr
reading /boot.scr
234 bytes read in 3 ms (76.2 KiB/s)
## Executing script at 80000000
reading zImage.itb
3360080 bytes read in 187 ms (17.1 MiB/s)
## Loading kernel from FIT Image at 82000000 ...
   Using 'config@1' configuration
   Trying 'kernel@1' kernel subimage
     Description:  ARM BeagleboneBlack Linux-4.1.13
     Created:      2016-03-20  22:33:34 UTC
     Type:         Kernel Image
     Compression:  uncompressed
     Data Start:   0x820000e8
     Data Size:    3325704 Bytes = 3.2 MiB
     Architecture: ARM
     OS:           Linux
     Load Address: 0x80008000
     Entry Point:  0x80008000
     Hash algo:    crc32
     Hash value:   62b34510
     Hash algo:    sha1
     Hash value:   04be40f903db0deb1cd632416e82f09828f05545
   Verifying Hash Integrity ... crc32+ sha1+ OK
## Loading fdt from FIT Image at 82000000 ...
   Using 'config@1' configuration
   Trying 'fdt@1' fdt subimage
     Description:  ARM Boneblack device tree blob
     Created:      2016-03-20  22:33:34 UTC
     Type:         Flat Device Tree
     Compression:  uncompressed
     Data Start:   0x8232c11c
     Data Size:    33030 Bytes = 32.3 KiB
     Architecture: ARM
     Hash algo:    crc32
     Hash value:   a101a6b3
     Hash algo:    sha1
     Hash value:   711dfa46a5cb4c8286035d1577fb6cc6eff22370
   Verifying Hash Integrity ... crc32+ sha1+ OK
   Booting using the fdt blob at 0x8232c11c
   Loading Kernel Image ... OK
   Loading Device Tree to 8fff4000, end 8ffff105 ... OK

Starting kernel ...

[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Initializing cgroup subsys cpuset
[    0.000000] Initializing cgroup subsys cpu

As I can see, u-boot detects the presence of boot.scr, follows the instruction given such as set the bootargs and 'fatload' the zImage.itb then boot Linux kernel. The part dealing with creating partitions and booting the image is done.

So far the method shown above is pretty much done at high level, booting up, deleting and recreating the partitions. Specifically, it is done at the OS level (Linux) while another alternative of creating/recreating eMMC partitions for this platform existed where it can be done at U-Boot level. The Boneblack can boot straight off the raw eMMC partition at fixed LBA offset if it is properly configured. To do this, I need to make sure the following flags, CONFIG_SYS_MMSD_RAW_MODE_xxx_SECTOR are set when building its SPL (MLO). The MLO and u-boot.img can then be copied to the eMMC raw partition at the fixed LBA offsets 0x100 and 0x300 respectively.

Boot from eMMC raw partition

. Follow doc/README.gpt on creating the GPT partition on the eMMC. This is what I have after creating four GPT partitions. Hint: Use host's tool uuidgen to generate the UUID needed.

Partition Map for MMC device 1  --   Partition Type: EFI

Part    Start LBA       End LBA         Name
        Attributes
        Type GUID
        Partition GUID
  1     0x00000022      0x00001021      "u-boot"
        attrs:  0x0000000000000000
        type:   ebd0a0a2-b9e5-4433-87c0-68b6b72699c7
        guid:   1377cef2-31f4-2341-bf92-706fe6b86817
  2     0x00001022      0x00002021      "env"
        attrs:  0x0000000000000000
        type:   ebd0a0a2-b9e5-4433-87c0-68b6b72699c7
        guid:   e54754d6-363e-8249-b30d-1f705412c6ba
  3     0x00002022      0x00007021      "kernel"
        attrs:  0x0000000000000000
        type:   ebd0a0a2-b9e5-4433-87c0-68b6b72699c7
        guid:   0d74cff8-8691-654a-b56c-468983a435b4
  4     0x00007022      0x00733fde      "rootfs"
        attrs:  0x0000000000000000
        type:   ebd0a0a2-b9e5-4433-87c0-68b6b72699c7
        guid:   3c6a05e6-e730-6e45-9fa5-a6e37b9283b6
U-Boot#

. Download MLO and u-boot.img and write to the eMMC raw partition. The fixed locations 0x100 and 0x300 fall into the u-boot partition (0x22..0x1021). Line 12,24 are mmc write to the fixed LBA offsets of the eMMC for 0x90 and 0x269 blocks where each block is 512 bytes.

. Download kernel image and write to the kernel partition. Having the named partition for it is not necessary , but it is easier to keep track of it later.

tftpboot $loadaddr zImage.itb
link up on port 0, speed 100, full duplex
Using cpsw device
TFTP from server 192.168.10.14; our IP address is 192.168.10.20
Filename 'zImage.itb'.
Load address: 0x82000000
Loading: *################################################################
         #################################################################
         ..

U-Boot# mmc write $loadaddr 2022 1b00

. Download root FS and write it to rootfs partition and set the u-boot's bootargs to specify the rootfs.

U-Boot# tftpboot $loadaddr rootfs.ext4
link up on port 0, speed 100, full duplex
Using cpsw device
TFTP from server 192.168.10.14; our IP address is 192.168.10.20
Filename 'rootfs.ext4'.
Load address: 0x82000000
Loading: *################################################################
         #################################################################
         ..
done
Bytes transferred = 130077696 (7c0d400 hex)
U-Boot# mmc write $loadaddr 7022 3e070

. Set/verify bootcmd to read kernel image from the correct LBA offset of the kernel partition as well as set/verify the bootargs to have the correct partition for the rootFS. The LBA offset for kernel partition above is at 0x2022.

U-Boot# pr bootcmd
bootcmd=mmc dev 1 && mmc read $loadaddr 2022 8200 && bootm $loadaddr
U-Boot# pr bootargs
bootargs=console=ttyS0,115200n8 root=/dev/mmcblk0p4 rw rootwait

The system should be able to boot and mount the rootfs correctly. The setting of bootcmd above is to read the kernel from LBA 0x2022 for 8200 blocks and boot from it. The bootargs is set to make sure that the rootfs is pointed to the 4th partition of the eMMC.

Of all the four GPT partitions created, the only partition that has FS is the rootfs while all others are raw partitions. This is almost similar to booting from NAND device.

Citations

1

https://buildroot.org

2

uImage.FIT directory of u-boot/doc

3

BBB_SRM.pdf, user reference manual of beagle bone black.