Working with USB in U-Boot

U-Boot provides various commands for working with USB devices, including scanning for USB storage, retrieving device information, and mounting file systems. This document will guide developers on how to perform these USB operations on the Mecha Comet device using U-Boot.

Prerequisites

• USB storage device (USB drive, external hard drive, etc.).
• Access to U-Boot mode on the Mecha Comet device. To do this, follow the steps outlined here:

Booting into Uboot

Enabling USB in U-Boot

Before interacting with USB devices, ensure that USB support is enabled in U-Boot. Run the following command to initialize the USB subsystem:

$ usb start

This command initializes the USB controller and detects connected USB devices. If the initialization fails, try resetting the USB subsystem with:

$ usb reset

This forces the re-enumeration of all connected USB devices.

Scanning for USB Devices

To detect and list all connected USB devices, use:

$ usb tree

Example Output:

USB device tree:
  1  Hub (480 Mb/s, 0mA)
  |  u-boot EHCI Host Controller
  |
  |+-2  Mass Storage (480 Mb/s, 500mA)
       SRT USB 3.0 JET 16G 049113121910253634000130

If devices are not detected, ensure that they are properly connected and powered.

Getting USB Device Information

To retrieve detailed information about connected USB devices, run:

$ usb info

Example Output:

1: Hub,  USB Revision 2.0
 - u-boot EHCI Host Controller
 - Class: Hub
 - PacketSize: 64  Configurations: 1
 - Vendor: 0x0000  Product 0x0000 Version 1.0
   Configuration: 1
   - Interfaces: 1 Self Powered 0mA
     Interface: 0
     - Alternate Setting 0, Endpoints: 1
     - Class Hub
     - Endpoint 1 In Interrupt MaxPacket 8 Interval 255ms

2: Mass Storage,  USB Revision 2.10
 - SRT USB 3.0 JET 16G 049113121910253634000130
 - Class: (from Interface) Mass Storage
 - PacketSize: 64  Configurations: 1
 - Vendor: 0x090c  Product 0x1000 Version 17.0
   Configuration: 1
   - Interfaces: 1 Bus Powered 500mA
     Interface: 0
     - Alternate Setting 0, Endpoints: 2
     - Class Mass Storage, Transp. SCSI, Bulk only
     - Endpoint 1 Out Bulk MaxPacket 512
     - Endpoint 2 In Bulk MaxPacket 512

If no devices are listed, check whether USB support is properly enabled in U-Boot.

Listing USB Storage Devices

If you have a USB storage device connected, list the available partitions using:

$ usb storage

To list all block devices (including USB storage), use:

$ ls usb 0

Mounting a USB Storage Device

To access files from a USB storage device, first check the filesystem type.

For FAT-formatted partitions:

$ fatls usb 0

Example Output:

   13012   boot.scr
   456789   uImage

For ext4-formatted partitions:

$ ext4ls usb 0

Example Output:

   20480   /boot/kernel.img
   10240   /boot/initrd.img

Loading a File from USB Storage

To load a specific file from the USB drive into memory:

For FAT-formatted partitions:

fatload usb 0:1 0x80000000 boot.scr

For ext4-formatted partitions:

ext4load usb 0:1 0x80000000 /boot/kernel.img

This loads the specified file into memory address 0x80000000 for further processing.

Booting from USB

To boot a kernel or script from a USB device, follow these steps:

1. Load the kernel into memory:

   fatload usb 0:1 0x80000000 zImage

   Or for ext4:

   ext4load usb 0:1 0x80000000 /boot/zImage
   

2. Load the device tree (if required):

   fatload usb 0:1 0x81000000 dtb
   

3. Boot the kernel:

   bootz 0x80000000 - 0x81000000
   

   The - signifies that no initrd is being used.

Writing to USB Storage

To write a file to a USB storage device in U-Boot, prepare the file in RAM and use the fatwrite or ext4write commands:

For FAT:

fatwrite usb 0:1 0x80000000 newfile.txt 1024

For ext4:

ext4write usb 0:1 0x80000000 /newfile.txt 1024

This writes 1024 bytes from memory address 0x80000000 to the specified file.

Unmounting and Stopping USB

After using the USB storage device, unmount and stop the USB subsystem:

usb stop

This safely stops USB operations before rebooting or removing the device.

Troubleshooting Common USB Issues

1. USB device not detected
   • Ensure usb start is executed.
   • Try usb reset.
   • Check hardware connections.
   • Verify U-Boot has USB support enabled.
2. File not found errors
   • Ensure the correct partition index is used (usb 0:1).
   • Verify the file exists with fatls or ext4ls.
3. Boot failure from USB
   • Ensure kernel and device tree are loaded correctly.
   • Use the correct memory addresses for bootz.

Conclusion

This guide covers the essential U-Boot USB commands on the Mecha Comet device, helping developers manage USB operations effectively. By following these steps, you can scan, mount, retrieve information, write to USB storage, and boot from USB devices in U-Boot.