Yocto U-Boot 4.1.15 features
This page is using the default release am62-yocto-kirkstone-6.1.46_09.01.00.08-v1.1.
To view this page for a specific Variscite SoM and software release, please follow these steps:
- Visit variwiki.com
- Select your SoM
- Select the software release
- If you manually upgrade U-Boot, and you have an old environment saved, it is a good idea to reset your environment to the new default (see Environment handling commands).
- (There is no need to do that manually if you install U-Boot using our recovery SD card image).
- If you manually upgrade U-Boot, and you have an old environment saved, it is a good idea to reset your environment to the new default (see Environment handling commands).
Notable features:
Splash Screen
A splash screen is enabled by default, and is shown on the LVDS LCD.
To disable the splash screen, enter the following in the U-Boot command line interface:
=> run splashdisable => saveenv && reset
And to re-enable it:
=> run splashenable => saveenv && reset
The splash image is taken from /boot/splash.bmp in the root file system.
Automatic Splash source selection
The splash image will be taken from whichever rootfs that is going to be mounted later at boot. To enable the automatic selection (already enabled by default):
$ setenv splashsourceauto yes $ saveenv
To disable the automatic selection:
$ setenv splashsourceauto no $ setenv splashsource YOUR_SELECTION $ saveenv
YOUR_SELECTION should be one of {sd, emmc}
Using your own LCD screen
There is support for the 800x480 LCD screen 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 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 USB 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:
=> ums 0 mmc $emmc_dev
To mount an SD card:
=> ums 0 mmc $sd_dev
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 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 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:00:00:02 => setenv usbnet_hostaddr f8:dc:7a:00:00:01 => 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 interaction.
- Note that you may need to configure your host PC to use the new network adapter properly - this configuration is OS dependent.
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 : => load mmc 0:2 /boot/splash.bmp
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
Using a USB Storage Device
Once you connected the device and stated the USB controller, you can now use the regular File System commands mentioned above with it.
The <interface> in this case is 'usb'.