There are 3 types of USB controller available on RK3399 SoC. Each type has 2 controllers, so in total there are 6 USB controllers. Below a description of each controller type.
### Generic OHCI USB 1.1 Controller
This controller is Host only controller that is compatible with USB 1.1.
Supported speeds:
- Full Speed (12 Mbps)
- Low Speed (1.5 Mbps)
### Generic EHCI USB 2.0 Controller
This controller is Host only controller that is compatible with USB 2.0. The controller shared port with
*Generic OHCI USB 1.1 Controller* therefore any USB 1.1 device connected to the port, will be automatically routed to *Generic OHCI USB 1.1 Controller*.
Supported speed:
- High Speed (480 Mbps)
### Synopsys DesignWare USB 3.0 Dual-Role Device Controller
This controller support On-The-Go / Dual Role which means it can be configured as Host or as Device.
Supported speeds:
- Super Speed (5 Gbps)
- High Speed (480 Mbps)
- Full Speed (12 Mbps)
- Low Speed (1.5 Mbps)
This controller is connected to RK3399 Type-C PHY.
* The first USB 3.0 Dual-Role Device Controller is connected to USB Type-C connector (J15) and configured as OTG with help of [FUSB302](https://www.onsemi.com/products/interfaces/usb-type-c/fusb302).
* The second USB 3.0 Dual-Role Device Controller is connected to USB Hub 3.1 Gen 1 and configured as Host only.
* One of EHCI Controller (and OHCI Controller) is connected to M.2 socket.
### Power Budget
Each external USB port is protected by a Power Distribution switch with following current limit.
Serial Console (UART2 Debug) of RK3399 SoC is connected to FT232 USB Serial converter and the USB 2.0 signal of the FT232 is connected to USB 2.0 signals of USB Type-C Port.
In case you are using the USB-C for one of the others functionalities but you still need to access SoC serial console for debug purpose, UART2 Debug is also exposed on P14 header.
Using USB Type-C to DisplayPort cable, Helios64 can be connected to monitor to display Linux Desktop or others GUI applications.
Using USB Type-C to HDMI cable/dongle, Helios64 can be connected to a TV and used as a media center.
*USB Type-C to HDMI dongle*
*USB Type-C to HDMI cable*
!!! note
- DisplayPort Alternate Mode is NOT supported on U-Boot.
- USB Type-C to HDMI cable might not work if it used DisplayPort dual mode (DP++).
### Host Mode
Using OTG cable (Type-C to Type A female) such as,
Helios64 can act as USB host and can be connected to various USB devices.
### Device Mode
Using Type-C to Type A male cable such as,
Helios64 can be used as Direct Attached Storage (DAS) with the required software configuration. It can also be used as "USB eMMC reader/writer" during system recovery mode.
USB Type C port is configured as USB Mass Storage connected to eMMC. This function, called UMS mode, can be activated by pressing [Recovery Button](/helios64/button/#ums-mode). This is to serve as a way to (re)install OS to eMMC.
The kernel module only exports the underlying block device NOT the filesystem layer. Therefore if the block device is formatted with filesystem unique to Linux, the exported disk may not be readable by the computer connected to Helios64 connected.
For example, if the block device is formatted with EXT4 filesystem and Helios64 connected to Windows PC as DAS, the Windows PC will not be able to read the disk content unless 3rd party software/driver installed.
Do NOT export block device(s) that you are also accessing via network (unless in read-only mode), as the filesystem of the exported block device cannot be managed concurrently and can lead to data corruption. Refer to kernel Mass Storage Gadget (MSG) [page](https://www.kernel.org/doc/html/latest/usb/mass-storage.html) to understand better the limitation.
Assuming the RAID array is already created and identified as /dev/md0, run the following command on Helios64 to export the RAID block device as USB Mass Storage
The following screenshots show Helios64 connected with 5x 120GB SATA disks and configured as RAID 6 so total space of the block device is ~360GB (3x 120GB). The block device is then formatted with NTFS.
