COM AM335x Bootloader U-Boot

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Q: Initialization of MAC address in the bootloader?
A: At the first start, the bootloader reads the MAC addresses (2x) from internal Control Module of the AM335x and creates env variable ethaddr and eth1addr. The env variable ethaddr or eth1addr could be changed during lifetime to any other MAC address. If you like to get back the original MAC address, please remove ethaddr, save environment and restart the system.
Q: The automatic update is not executed before the operating system boots!
A: Check if the command update auto is included in the bootloader environment variable bootcmd or in a script-variable which is called within bootcmd before bootm .
Q: The automatic update does not work with my desired update-media!
A: The command update auto can be configured with flags within the DHCOM settings.bin block. It is possible to disable a interface for the update mechanism. You can run a update from a disabled interface if you use the command update without the argument auto . Take care about the correct setup of your media.


Please have a look at the AM335x Downloads section.

Enter Bootloader Console

  1. Connect DHCOM UART1) via null modem cable to the RS232 Port of your PC
  2. Start terminal program (e.g. Tera Term) on the Host PC with the following settings:
    Baud rate: 115200
    Data: 8 bit
    Parity: none
    Stop bits: 1 bit
    Flow control: none
  3. Press "del" on the Host PC during Core Module system start to enter bootloader console

U-boot console commands

SPI Flash

SPI Flash Init
sf probe
Example: sf probe
Description: Initializes the OnBoard SPI Flash
SPI Flash Read
sf read <SDRAM address> <SPI Flash address> <Bytes>
Example: sf read 80000000 0 100
Description: Copies 256Bytes from SPI Flash address 0x0 to SDRAM address 0x1000_0000
SPI Flash Write
sf write <SDRAM address> <SPI Flash address> <Bytes>
Example: sf write 80000000 40000 10000
Description: Copies 64kByte from SDRAM address 0x8000_0000 to SPI Flash address 0x4_0000
SPI Flash Erase
sf erase <SPI Flash address> <Bytes>
Example: sf erase 100000 1000
Description: Deletes SPI Flash content from address 0x10_0000 to 0x10_0FFF
Note: The Bytes information needs to be sector size aligned!


We provide the DHCOM AM335x with NAND or eMMC. The following commands are reserved for the NAND version of DHCOM AM335x.

Read from NAND-Flash Device
nand read <SDRAM address> <NAND Flash address> <Bytes>
Example: nand read 80000000 400000 b40000
Description: Copies 11,25MByte from NAND Flash address 0x40_0000 to SDRAM address 0x8000_0000
Erase NAND-Flash blocks
nand erase <Block base address> <Bytes>
Example: nand erase 400000 40000
Description: Deletes NAND Flash content from address 0x40_0000 to 0x43_FFFF
Note: The Bytes information needs to be block size aligned!
Write to NAND-Flash Device
nand write <SDRAM address> <NAND-Flash address> <Bytes>
Example: nand write 80000000 400000 b40000
Description: Copies 11,25MByte from SDRAM address 0x8000_0000 to NAND Flash address 0x40_0000
Note: The Bytes information needs to be page size aligned!
Show bad NAND-Flash blocks
nand bad
Description: Shows the bad NAND-Flash blocks.
Show NAND-Flash content
nand dump <NAND-Flash address>
Example: nand dump 400000
Description: Shows the content of the specified NAND-Flash block

UBI Filesystem

Partition Definition
Example: mtdparts
Description: Shows the current nand flash partitions. In case of AM335x one default partition set, which includes the entire flash. For linux that partition is used to create two volumes "boot" and "rootfs".
Note: In case of UBIFS it is better to have one big partition with different volumes instead of many small partitions, because the wear leveling process is always applied to every partition.
device nand0 <gpmi-nand>, # parts = 1
#: name                size            offset          mask_flags
0: gpmc-nand           0x20000000      0x00000000      0
active partition: nand0,0 - (gpmc-nand) 0x20000000 @ 0x00000000
Set or show active partition
ubi part <partition name>
Example: ubi part gpmi-nand
Description: Show or set current partition. In AM335x default case this is shold always set to gpmc-nand.
Mount UBI volume
ubifsmount <UBI device>:<volume name>
Example: ubifsmount ubi0:boot
Description: Mount UBIFS volume. The default name of the first AM335x volume is "boot".
List files
ubifsls <directory>
Example 1: ubifsls
Description: List files in a UBIFS directory.
Load Files from UBI volume
ubifsload <SDRAM address> <directory+filename>
Example 1: ubifsload 10100000 zimage
Description: Load file from an UBIFS filesystem to memory.
Unmount UBI volume
Example: ubifsumount
Description: Unmount current volume.


Switch between MicroSD, SD Slot and eMMC
mmc dev <Slot number> <Partition number>
Example: mmc dev 0
Description: Switch between SD/MMC Slots:
  • 0 --> SD/MMC or MicroSD Slot
  • 1 --> eMMC Flash
Initialize SD/MMC Card
mmc rescan
Description: Initialize new inserted SD Card
Show SD/MMC information
Description: Shows SD/MMC device information
Device: FSL_SDHC
Manufacturer ID: 45
OEM: 100
Name: SEM08
Tran Speed: 52000000
Rd Block Len: 512
MMC version 4.41
High Capacity: Yes
Capacity: 7.3 GiB
Bus Width: 8-bit
Write to MicroSD, SD Slot and eMMC
mmc write <SDRAM address> <block number> <block count>
Example: mmc write 81000000 5000 400
Description: Write 512kByte (device block size is 512Byte) to the eMMC offset 10MByte.
Read from MicroSD, SD Slot and eMMC
mmc read <SDRAM address> <block number> <block count>
Example: mmc read 81000000 5000 400
Description: Read 512kByte (device block size is 512Byte) from the eMMC offset 10MByte.

FAT - EXT2 - EXT4 - Filesystem

NOTE: All EXT2 commands must also be used for ext4
Show Filesystem information
fatinfo <interface> <device>
Example: fatinfo mmc 1
Interface: MMC
 Device 1: Vendor: Man 094150 Snr 266e068c Rev: 1.0 Prod: AF UD
           Type: Removable Hard Disk
           Capacity: 121.2 MB = 0.1 GB (248320 x 512)
 Partition 1: Filesystem: FAT16 "NO NAME    "
List files
fatls <interface> <device> <directory>
ext2ls <interface> <device> <directory>
Example 1: fatls mmc 1
Example 2: fatls mmc 1 /folder
Load Files from SD Card to SDRAM
fatload <interface> <device> <SDRAM address> <directory+filename>
ext2load <interface> <device> <SDRAM address> <directory+filename>
Example 1: fatload mmc 1 80100000 nk.gz
Example 2: fatload mmc 1 80100000 /folder/nk.gz


Load File via TFTP to SDRAM
tftp <SDRAM address> <directory+filename>
Example: tftp 80100000 nk.gz
Example TFTP Server: "Winagents TFTP Server Manager"
Note: For TFTP download it is necessary to config the ENV variables "ipaddr" and "serverip"
Load File via TFTP to SDRAM using DHCP
dhcp <SDRAM address> <directory+filename>
Example: dhcp 80100000 nk.gz
Example TFTP Server: "Winagents TFTP Server Manager"
Note: It is necessary to config the ENV variable "serverip" with the ip-address of your TFTP-Server
ping <IP address>
Example: ping
Read PHY register via MII interface
mii dump <PHY address> <PHY register>
Example: mii dump 0 0
Remark: The standard MII registers 0-5 are supported by this command.


unzip <source address> <destination address>
Example: unzip 82900000 80100000
Note: The unzip command is supporting the gzip file format.


bmp info <Bitmap address>
Image size    : 800 x 480
Bits per pixel: 8
Compression   : 0
bmp display <Bitmap SDRAM address> [x y]
Note: It is necessary to load bitmap file to memory address with an offset of an odd multiple of +2, since the use of a four-byte alignment will cause alignment exceptions at run-time.


md[.b, .w, .l] <address> [count]
Example: md.b 80100000 100
mw[.b, .w, .l] <address> <value> [count]
Example: mw.b 80100000 aa 100
Description: Writes the value 0xaa to the next 0x100 bytes from the address 0x8010_0000.
cp[.b, .w, .l] <source> <destination> <count>

Show DHCOM Settings

 DISPLAY_ID:       0x00
 LENGTH:           0x2c
 X_RESOLUTION:     800 pixel
 Y_RESOLUTION:     480 pixel
 PIXEL_CLOCK:      22200 kHz
 HSW:              64 pixel clocks
 VSW:              2 line clocks
 HFP:              42 pixel clocks
 HBP:              86 pixel clocks
 VFP:              10 line clocks
 VBP:              33 line clocks
 DATALINES:        16
 ACB:              0
 ACBI:             0
 GPIO_DIR:         0x01ff
 GPIO_STATE:       0x0000


List available devices
i2c probe
Valid devices:
0 = OnBoard I2C portDHCOM I2C port 1
1 = not connected
2 = DHCOM I2C port 1
i2c md <I2C address> <start address> <end address>
Example: i2c md 57 10 20
Description: Reads 16 Bytes from the address 0x10 to address 0x20.
i2c mw <I2C address> <I2C register> <Value> <Bytes>
Example: i2c mw 57 0 aa 5
Description: Writes 0xaa to 5 Bytes from the offset 0.


Print Variables

env print

Set Variables

env set [-f] name [arg ...]

Example: env set ipaddr

Note: If you need to edit "bootcmd" it is necessary to insert ";" between the unique commands. You can enter ";" at the command line with "\;".

Save Variables

env save

Delete Variable

env delete <ENV name>

Revert Complete Environment to Default

env default -a

Import from Textfile

env import -t <SDRAM address> $filesize


fatload mmc 0 0x10000000 uEnv.txt
env import -t 0x10000000 $filesize

Important: The uEnv.txt file should be in unix format. Also make sure that there is an empty line at the end of the file.

How to do Updates

Display and Hardware settings

DHCOM settings and Splash bitmap

The DHCOM settings are used to setup display and special hardware parameters. For detailed description please have a look at How to create a settings.bin file.
The DHCOM settings file and the splash bitmap are loaded via the env variables "load_settings_bin" and "load_splash" during startup from boot partition. The default content of these env variables is:
load_settings_bin=load mmc ${mmcdev}:${mmcpart} ${loadaddr} ${settings_bin_file}
load_splash=load mmc ${mmcdev}:${mmcpart} ${splashimage} ${splash_file}
Note: The DHCOM display settings can also be stored in external eeprom (address 0x50 / 7bit I2C address) which is connected to DHCOM I2C1 port. If eeprom is available and DISP_ADPT_EEPRM flag is set to 1, the settings from eeprom override the settings from boot partition!
Next you can see the settings load order:
DISP ADPT EE check.png

Displaying a splash screen with u-boot


  • This is possible with u-boot version v0.1.0.0 or newer.
  • Only RGB interface is supported.

The process to set it up is the following:

  • Configure your display parameters with DHCOM settings generator (How to create a settings.bin file)
  • Generate settings bin file with settings generator.
  • Copy settings bin file to boot partition on boot media (eMMC, NAND or microSD card).
  • Generate your splash bitmap (bitmap with 8 bit color depth).
  • Copy also bmp file to boot partition.
  • Start DHCOM module and enter u-boot console.
  • Set env variable “settings_bin_file” with settings bin filename:
    Example: env set settings_bin_file 10_LG_7inch_LB070WV8.bin
  • Set env variable “splash_file” with bitmap filename:
    Example: env set splash_file 800x480_splash_DHCOM_iMX6.bmp
Remark: This can be done in the uLinuxEnv.txt, too.
  • Save u-boot environment to flash: saveenv
  • Restart the system --> Splash bitmap should now be displayed from the bootloader.

Display disabled by default

With default u-boot configuration u-boot doesn't initialize the Display interface. This feature can be activated by deleting the "panel" environment variable. But also with deactivated display interface, the bootlaoder reads the display settings and pass the settings to the linux kernel.
panel="no_panel": Display interface is deactiveted in u-boot and backlight is powered off.
panel="RGB": Default DH 4,3" display is selected.
panel=deleted: u-boot initialize display by DH settings file.

Backlight enable GPIO

If ENV variable "panel" is set to "no_panel" the backlight enable GPIO (defined via DHCOM settings file or eeprom settings) will be disabled from the bootloader during startup.
If ENV variable "panel" is deleted, the backlight enable GPIO is activated or deactivated in relation to BL_ON flag of DHCOM settings file.
Note: Supported by U-Boot DH VERSION v0.4.2.5 or higher for iMX6

Building U-Boot (and MLO)

Prepare Build Environment

Get Sources

1. Start a terminal on Linux
2. # git clone
3. # cd u-boot-am33x
4. # git checkout release/v0.4.0.1 # checkout latest/required branch or tag

Start Build

6. # ./uboot_make [nand] # add argument 'nand' to include nand support, not suitable for eMMC devices

  • Your new u-boot.img file is available in u-boot-am33x/
  • If your build does fail please check content of uboot_make and adjust PATH.
  • Use MLO.byteswap if you need to replace the MLO.

Attention: Risk of bricking the Device!!