diff --git a/docs/helios64/img/usb/otb_cable_usb_c.jpg b/docs/helios64/img/usb/otb_cable_usb_c.jpg
new file mode 100644
index 0000000..21c4b75
Binary files /dev/null and b/docs/helios64/img/usb/otb_cable_usb_c.jpg differ
diff --git a/docs/helios64/img/usb/usb_diagram.png b/docs/helios64/img/usb/usb_diagram.png
new file mode 100644
index 0000000..5ece80d
Binary files /dev/null and b/docs/helios64/img/usb/usb_diagram.png differ
diff --git a/docs/helios64/img/usb/usb_mux.png b/docs/helios64/img/usb/usb_mux.png
new file mode 100644
index 0000000..69c182d
Binary files /dev/null and b/docs/helios64/img/usb/usb_mux.png differ
diff --git a/docs/helios64/usb.md b/docs/helios64/usb.md
new file mode 100644
index 0000000..8b7a165
--- /dev/null
+++ b/docs/helios64/usb.md
@@ -0,0 +1,161 @@
+
+
+## USB on RK3399
+There are two types of USB controller available on RK3399. Each type has two controller so total USB controllers is 4.
+
+### Generic EHCI USB 2.0 Controller
+There are two controller of this type. This controller is Host only controller that is compatible with USB 2.0 and backward compatible with USB 1.1.
+Supported speed:
+
+- High Speed (480 Mbps)
+
+- Full Speed (12 Mbps)
+
+- Low Speed (1.5 Mbps)
+
+
+### Synopsys DesignWare USB 3.0 Dual-Role Device Controller
+There are two controller of this type. This controller support On-The-Go /Dual Role which mean it can be configured as Host and also Device.
+Supported speed:
+
+- Super Speed (5 Gbps)
+
+- High Speed (480 Mbps)
+
+- Full Speed (12 Mbps)
+
+- Low Speed (1.5 Mbps)
+
+The controller is connected to Rockchip Type-C PHY.
+
+## USB on Helios64
+
+![!USB Connection](/helios64/img/usb/usb_diagram.png)
+
+One of EHCI Controller is connected to M.2 socket.
+
+The first Synopsys DesignWare USB 3.0 Dual-Role Device Controller is connected to USB Type-C connector and configured as OTG with help of FUSB302.
+
+The second Synopsys DesignWare USB 3.0 Dual-Role Device Controller is connected to USB Hub 3.1 Gen 1 and configured as Host only.
+
+### Power Budget
+
+Each of external USB port is protected by Power Distribution switch with following current limit.
+
+| Port | Voltage | Maximum Current | Remarks |
+|------------|-------|------------------|---------|
+| USB 3.0 Upper Back Panel | 5V | 900 mA | |
+| USB 3.0 Lower Back Panel | 5V | 900 mA | |
+| USB 3.0 Front Panel | 5V | 900 mA | |
+| Type-C | 5V | 1200 mA | PDO source only |
+
+
+## USB Type-C Functionality on Helios64
+
+To simplify the cabling, Helios64 is designed to have 
+
+![!USB Mux](/helios64/img/usb/usb_mux.png)
+
+### Serial Console
+
+Serial Console of Helios64 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.
+Refer to ***JUMPER PAGE***
+
+
+### DisplayPort Alternate Mode
+
+Using USB Type-C to DisplayPort cable or USB Type-C to HDMI dongle, Helios64 can be connected to monitor to display Linux Desktop or other GUI application.
+
+*** Put USB Type-C to DisplayPort cable photo here ***
+
+*** Put USB Type-C to HDMI dongle photo here ***
+
+!!! note
+    DisplayPort Alternate Mode is NOT supported on U-Boot.
+
+
+### USB Host
+
+Using OTG cable such as,
+
+![!USB-C OTG Cable](/helios64/img/usb/otb_cable_usb_c.jpg)
+
+Helios64 can act as USB host and can be connected to various USB device.
+
+### USB Device
+
+Helios64 can be used as Direct Attached Storage (DAS) with proper configuration and kernel module. Refer to [Helios64 as Direct Attached Storage (DAS) device](#helios64-as-direct-attached-storage-das-device)
+
+Helios64 can also used as "USB eMMC reader/writer" for OS recovery purpose. Refer to [USB OTG Port (USB Type-C)](#usb-otg-port-usb-type-c)
+
+
+## USB under U-Boot
+
+### USB Host Port
+
+USB Host support in U-Boot is quite minimal, it only support USB storage and USB ethernet.
+
+### USB OTG Port (USB Type-C)
+
+USB Type C port is configured as USB device mode as USB Mass Storage connected to eMMC.
+This function can be activated by pressing Recovery Button.
+This is to serve as a way to (re)install OS to eMMC.
+
+
+## USB under Linux
+
+### USB Bus Mapping
+
+| USB Controller | Bus number | Remarks |
+|----------------|------------|---------|
+| EHCI Host0 | 0 | |
+| EHCI Host1 | 1 | |
+| DWC3 Typec0 USB 3.0 | 2 |  |
+| DWC3 Typec0 USB 2.0 | 3 |  |
+| DWC3 Typec1 USB 3.0 | 4 |  |
+| DWC3 Typec1 USB 2.0 | 5 |  |
+
+-----  ***TBC***  ------
+
+### Helios64 as Direct Attached Storage (DAS) device
+
+Helios64 can be used as Direct Attached Storage (DAS) device with help of Linux USB Gadget kernel module.
+
+The kernel moodule only export 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 readable by computer that has Helios64 connected to.
+
+For example, 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.
+
+
+!!! warning
+    Do NOT access Helios64 simultanouesly as DAS and NAS, as the filesystem is not managed by system and can lead to data corruption.
+
+
+#### Individual Disk Exported as Separate Disk
+
+----- ***more info soon*** -----
+
+```
+modprobe g_mass_storage file=/dev/sda,/dev/sdb,/dev/sdc,/dev/sdd,/dev/sde
+```
+
+----- *** Put Windows Explorer & Disk management screenshot here *** ----- 
+
+----- *** Put lsusb & lsblk here *** ----- 
+
+
+#### RAID device exported as One Disk
+
+----- ***more info soon*** -----
+
+```
+modprobe g_mass_storage file=/dev/md/md-raid6
+```
+
+----- *** Put Windows Explorer & Disk management screenshot here *** ----- 
+
+----- *** Put lsusb & lsblk here *** ----- 
+
+
+
diff --git a/mkdocs.yml b/mkdocs.yml
index e5ee27d..7f43e10 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -79,6 +79,7 @@ nav:
     - GPIO : 'helios64/gpio.md'
     - I2C : 'helios64/i2c.md'
     - LED : 'helios64/led.md'
+    - USB : 'helios64/usb.md'
 - Helios4:
   - Introduction: 'helios4/intro.md'
   - Kit Assembly: 'helios4/kit.md'