Billboard- A Must-Know for Type-C Device Holders

With the widespread of the USB Type-C interface and its innovative features such as image transmission, charging, sound effect, and internet, Type-C is getting increasingly popular. Despite its various functions, Type-C faces issues when connected to a non-supporting device. This is where Billboard plays the key role as it instantly informs users the issues.

• Who defined Billboard?
• USB-IF announced the specifications of Power Delivery v2.0 in 2014 and simultaneously defined the new Billboard Device Class v1.0 in the original USB Class
• What is Billboard?
• First we need to understand the Type-C connection mode:
  Alternate Mode: For example, PD, DisplayPort Alternate Mode (DP Alt Mode)
• Billboard Device Class
  When a device which supports Alternate Mode is connected to a non-supporting host device, a pop-up window, or the Billboard, will show information of the device status. Billboard notifies users the status of use when the device does not support Alternate Mode.
• When does Billboard show up?
  When the device can correctly communicate and is recognized as an Alternate Mode device, i.e., when a monitor that supports Type-C interface is connecting via Type-C and the device manager is accurately recognized as a monitor, the communication is then conducted in Alternate Mode with images being displayed normally.

On the other hand, if a monitor that supports Type-C interface connects via Type-C but is not recognized as Alternate Mode, the OS will recognize the device as USB Billboard device, as shown in Figure 1.

Figure 1

A Billboard message will pop up in the lower-right corner of the desktop to alert users of the current device status, as shown in Figure 2.

Figure 2

• How to enter Billboard mode?
  The first condition for triggering Billboard pop-up is if a device is unable to enter Alternate Mode. When Alternate Mode completes communication and is deemed to be not executable, Billboard device will appear.
• tAMEtimeout: A timer; if communication is not completed within 1.5-second, it will directly enter Billboard mode.
• If a device uses its self-defined static functions list, Billboard device will appear and recognize it as unspecified error before entering Alternate Mode.
• If the device has successfully entered Alternate Mode, but subsequent errors are detected under Alternate mode, a Billboard message pop-up will be displayed to alert the user.
• If a malfunction occurs while two Type-C ports are communicating and leads to the exit of Alternate Mode, a Billboard message pop-up will be displayed to alert the user.
• How is Billboard message presented?
  Billboard message is stored in BOS descriptor, a user-defined character string. When unable to enter Alternate Mode, the system will call up the character string defined by the vendor in BOS descriptor and display it in Billboard message, as shown in figures below:

Figure 3

Figure 4

Figure 5

• Likely Occurrences of Billboard in Daily Lives
  Based on Allion’s tests results, the following two scenarios are most likely to occur: Use of Type-C to Type-A USB cable, as shown in figure below:

Figure 6

Due to the use of the lower-speed Type-A interface, it is unable to enter Alternate Mode, which is only supported by Type-C to Type-C. Therefore, a Billboard message pop-up will be displayed.

• Type-C port system used does not support Alternate Mode, as shown in figure below:

Figure 7

As the system itself could be an older version , it cannot support Alternate Mode. Therefore, a Billboard message pop-up will be displayed to alert users.

Since the Type-C interface is very likely to dominate the PC and home appliance markets in the future, for devices that are unable to enter Alternate Mode, it is necessary to make it known to consumers  that the transmission is currently not in high-speed mode, enabling  consumersto use the device after being well-informed.