U-Boot features
New features introduced in Variscite U-Boot 2015.04:
Splash Screen
A splash screen is enabled by default, and is shown on the LVDS LCD.
To disable the splash screen, stop the boot at u-boot command prompt and enter:
=> run disable_splash => saveenv && reset
And to re-enable it:
=> run enable_splash => saveenv && reset
The splash image is taken from /boot/splash.bmp in the root file system.
Notes:
- The splash image will be taken from whichever rootfs that is going to be mounted later at boot.
- In case the rootfs is a UBIFS, mounting it in order to load the splash file will add ~1.8 seconds to the boot time.
Using your own LVDS LCD screen
There is support for the three different 800x480 LCD screen types that Variscite uses.
If you want to add support for a different LCD that is not currently supported, you need to edit the displays array in board/variscite/mx6var_som/mx6var_som.c in the U-Boot source code, according to your LCD parameters.
USB Mass Storage gadget
You can use the board as a USB Mass Storage device:
You will be able to access all the partitions of any block device that is on the board or connected to it, from your host PC - You will see them as /dev/sdXX, just like connecting a regular USB storage to your PC, and you'll be able to mount them, and have full read/write access to them. You can even use it to flash a new U-Boot, re-partition the storage, re-format it, etc.
This is especially useful for updating the internal eMMC.
To do this you need to connect a USB cable between the OTG/Client port of the board and a regular USB Host port on your PC, and use U-Boot's ums command.
General ums usage is:
ums <USB_controller> [<devtype>] <devnum> e.g. ums 0 mmc 0
devtype defaults to mmc
devtype can be any block device (e.g. mmc, usb)
To mount the eMMC:
On any SOM other than DART-MX6: => ums 0 mmc 1 On a DART-MX6 SOM when booting from SD card: => ums 0 mmc 1 On a DART-MX6 SOM when booting from eMMC: => ums 0 mmc 0
To mount an SD card:
On any SOM other than DART-MX6: => ums 0 mmc 0 On a DART-MX6 SOM when booting from SD card: => ums 0 mmc 0 On a DART-MX6 SOM when booting from eMMC: => ums 0 mmc 1
Depending on your host PC, it may automatically mount it or not. If not, you can use dmesg to see the names of the device and its partitions (it should be in the form of /dev/sdXX) and mount them yourself.
To exit the ums command and disconnect the USB device press ctrl+c.
Note: You should use a Linux PC host as Windows can't naturally read ext file systems.
USB Ethernet Gadget
The USB Ethernet gadget allows you to make the board act as a USB Ethernet device when connecting its USB OTG/Client port to a host PC using a USB cable.
Basically, it allows for "Ethernet over USB".
This is especially useful if you build a custom board without an Ethernet interface and you want to boot via network using TFTP.
This feature is disabled by default. To enable it, you need to un-comment the defines of the following configs in include/configs/mx6var_som.h in the U-Boot source code:
CONFIG_USB_ETHER
CONFIG_USB_ETH_CDC
Now you should have a new Ethernet interface called usb_ether.
Before actually using it you should get to know the following environment variables:
Variables specific to this gadget:
usbnet_devaddr - The virtual MAC address of the device (the board side). usbnet_hostaddr - The virtual MAC address of the host (the PC side).
General network variables:
ethprime - Sets the primary Ethernet interface. This is the interface that will be tried first. ethact - Sets the currently active Ethernet interface. Normally, it is modified by the Ethernet driver, but you can change it if you want to override. ipaddr - IP address of the device - needed for tftp command. netmask - Subnet Mask. serverip - TFTP server IP address - needed for tftp command.
So, for example:
=> setenv usbnet_devaddr f8:dc:7a:00:00:01 => setenv usbnet_hostaddr f8:dc:7a:00:00:02 => setenv ethact usb_ether => setenv ipaddr 192.168.0.100 => setenv netmask 255.255.255.0 => setenv serverip 192.168.0.101
And now your are ready to use tftpboot over the usb_ether interface.
Notes:
- Once you run a network command, e.g. tftpboot, the gadget will be connected to your host PC and a new network adapter will be added to it, for the duration of the network ineraction.
- Note that you may need to configure your host PC to use the new network adapter properly - this configuration is OS dependent.
HDMI auto-detection
If an HDMI screen is connected to the board, it will auto-detect it on boot and use it as its display.
No need to manually change anything.
What it actually does is use the hdmidet command to detect the hdmi and automatically add "video=mxcfb0:dev=hdmi,1920x1080M@60,if=RGB24;" to bootargs, accordingly.
Host/Client mode on VAR-MX6CustomBoard's micro-USB port
On VAR-MX6CustomBoard the micro-USB port is not a fully native OTG - it supports either Client or Host mode.
When using it in U-Boot, it is set to Client mode by default and you can change it to Host mode by setting the following environment variable:
=> setenv usbmode host
You can change it back and forth in real time when using this USB port in U-Boot, but pay attention that you are using the USB port correctly, according to the mode you set it to.
Note: The rest of the USB ports on VAR-MX6CustomBoard are always Hosts.
Choosing Root File System location when booting from NAND
If you're using a SOM with both NAND flash and eMMC, and you want to manually set the rootfs location to eMMC when booting from NAND, set the following environment variable:
=> setenv chosen_rootfs emmc
Otherwise, it will try to mount the rootfs from NAND.
What it actually does is choose between running "run bootargs_ubifs" or "run bootargs_emmc" which sets bootargs accordingly:
bootargs_ubifs=setenv bootargs console=${console},${baudrate} ubi.mtd=3 root=ubi0:rootfs rootfstype=ubifs; run videoargs
bootargs_emmc=setenv bootargs console=${console},${baudrate} root=/dev/mmcblk1p1 rootwait rw; run videoargs
Note: If you use our NAND/eMMC recovery SD card ver. 50 and above to flash Yocto, the chosen rootfs will be updated automatically to the location that you install the rootfs to - no need to manually change the environment.
DART-MX6 features previously missing
- U-Boot now supports both SD card and eMMC at the same time, also on DART-MX6 SOMs, regardless of where you boot from.
- On DART-MX6 SOMs, the device you boot from is always mmc 0, and the other is mmc 1.
- U-Boot now supports USB also on DART-MX6 SOMs.
Other Variscite U-Boot features
Automatic Device Tree selection
Automatic Device Tree selection
Disable Automatic Device Tree selection
General U-Boot commands
List all supported commands and their description/usage (help command)
List all supported commands with a brief description for each one:
=> help
Print the description and usage of 'command':
=> help command
Environment handling commands
Print the values of all environment variables:
=> printenv
Print value of environment variable 'name':
=> printenv name
Set environment variable 'name' to 'value ...':
=> setenv name value ...
Delete environment variable 'name':
=> setenv name
Reset default environment:
=> env default -a
Save environment variables to persistent storage:
=> saveenv
File System access
List files in a directory (default /):
=> ls <interface> [<dev[:part]>] [directory]
For example:
List files in the BOOT partition of our NAND/eMMC Recovery SD card (after booting from it): => ls mmc 0:1 List files in directory /opt/images/Yocto in the rootfs partition of our NAND/eMMC Recovery SD card (after booting from it): => ls mmc 0:2 /opt/images/Yocto
Load binary file 'filename' from a partition to RAM address 'addr':
=> load <interface> [<dev[:part]> [<addr> [<filename> [bytes [pos]]]]]
For example:
Load /boot/splash.bmp from the rootfs partition of our NAND/eMMC Recovery SD card (after booting from it) to RAM address 0x18100000: => load mmc 0:2 0x18100000 /boot/splash.bmp
UBI File System
This is the FS we use on our NAND flash.
UBIFS is very different to any traditional file system - it does not work on top of block devices (like hard drives, MMC/SD cards, USB flash drives, SSDs, etc).
UBIFS was designed to work on top of raw flash.
The usage is a little different than using FAT/ext.
Before you can access the UBIFS you need to mount it first:
=> ubi part rootfs => ubifsmount ubi0:rootfs
Now you can access the UBIFS with the regular commands above.
The <interface> in this case is ubi, <dev> can be anything (the value is ignored) and part is not necessary.
For example:
List files in directory /home/root on the mounted UBI file system: => ls ubi 0 /home/root
When finished accessing it, unmount the FS:
=> ubifsumount
USB sub-system
To use the USB as host (connect a USB Storage or Ethernet Device to the board), you need to use the usb command.
Usage:
usb start - start (scan) USB controller
usb reset - reset (rescan) USB controller
usb stop [f] - stop USB [f]=force stop
usb tree - show USB device tree
usb info [dev] - show available USB devices
usb test [dev] [port] [mode] - set USB 2.0 test mode
(specify port 0 to indicate the device's upstream port)
Available modes: J, K, S[E0_NAK], P[acket], F[orce_Enable]
usb storage - show details of USB storage devices
usb dev [dev] - show or set current USB storage device
usb part [dev] - print partition table of one or all USB storage devices
usb read addr blk# cnt - read `cnt' blocks starting at block `blk#'
to memory address `addr'
usb write addr blk# cnt - write `cnt' blocks starting at block `blk#'
from memory address `addr'
First, connect your device to a USB port on the board.
After the device is connected, start the USB controller:
=> usb start
If you connect/disconnect devices after that, before you can access them you need to rescan the USB controller:
=> usb reset
Flashing UBIFS to NAND using U-Boot
The best way to flash a UBI image is by using ubiformat (which is a part of mtd-utils) under Linux, as it preserves erase counters.
But if you flash the UBIFS only once, then it doesn't matter because there are no erase counters to preserve.
Assuming you are reading the UBI image from our Recovery SD card:
load mmc 0:2 0x18100000 /opt/images/Yocto/rootfs.ubi.img nand erase.part rootfs nand write.trimffs 0x18100000 rootfs $filesize
Note: There is another method to do this using U-Boot that preserves erase counters, using the higher level ubi command, but you need a UBIFS image for it:
load mmc 0:2 0x18100000 /opt/images/Yocto/rootfs.ubifs ubi part rootfs ubi remove rootfs ubi create rootfs ubi write 0x18100000 rootfs $filesize