Mandate: Required
Effective Date: April, 2005
The success of USB has been achieved by ensuring a consistent, reliable and enjoyable consumer experience. Translated, this means USB devices "just work." Consumers have come to expect a USB device to become quickly available and usable when attached to the bus. Now, with USB expanding into an ever widening array of applications and industries, it is important to continue to meet the consumer's expectations regarding USB in these new applications.
The USB-IF enforces a "no silent failure" rule. This means that an implementation of USB must not appear broken to the consumer. In configurations where the consumer's expectations are not met, either the peripheral or host must provide appropriate and useful feedback to the consumer regarding the problem.
Example 1:
Embedded hosts are, by definition, limited in capabilities. Should a consumer attach, to an embedded USB host, a USB peripheral that is not supported, nothing will happen. Without appropriate messaging, frustration and negative experience can occur as the consumer attempts to troubleshoot why the peripheral does not work. In this example, the embedded host would be the device to display an appropriate message informing the user that the device is not supported. Thus, embedded hosts are required to communicate a message to the consumer when an attached peripheral is not supported. The message should be specific and helpful for the consumer.
Example 2:
High-speed devices are required to enumerate and operate when attached to a full-speed port. However, there are some devices that require bandwidth far greater than 12Mbps making them useless at full-speed. Examples include high-speed video cameras that stream uncompressed, high resolution content. Without appropriate messaging, the consumer would either see garbled video or no video at all with such a camera attached at full-speed. In this example, the camera would be the device responsible for displaying an appropriate message to the consumer.
Different messages for hubs and non-hubs are required. If the attached peripheral is a hub, the embedded host must be able to display a message indicating that the attached hub is not supported. Care should be taken to distinguish between standalone hubs and compound peripherals. If an unsupported hub is attached, the embedded host should read bit D2 the wHubCharacteristics field of the hub descriptor and display the appropriate message in case the attached hub is part of a compound peripheral.
Top Mandate: Optional
Effective Date: n/a
Top Mandate: Required
Effective Date: October, 2007
The automotive USB embedded host cannot be certified without the cable harness because it does not offer the appropriate receptacle. The USB-IF has agreed with the automotive manufacturers to allow certification of the USB embedded host along with the actual cable harness with which it would be installed. Automotive embedded hosts may be submitted for certification along with the cable (harness) that will be used in the final installation and the certification will apply to the device and cable together.
In-dash automotive embedded hosts are still subject to the requirements defined in the "Embedded Host Compliance Plan" with the exceptions outlined in this update.
Since an automotive manufacturer will typically implement the USB embedded host in several different vehicle models, and since it is likely that those different vehicles will each require a different cabling layout, the USB-IF has further agreed to allow manufacturers to submit the USB device with the longest and shortest cable harnesses from the same manufacturer to be used, and that would qualify a passing product to be eligible to use the logo with both of those cables and with any intermediate length cables of a similar style and manufacturer.
Manufacturers are highly encouraged to limit cable lengths to a meter or less in order to obtain the best signal quality. The use of hub electronics at the location where the Standard-A receptacle is presented to the user is encouraged to provide the highest reliability.
Top Mandate: Required
Effective Date: June, 2013
The USB-IF started the certification program for embedded hosts in 2006. Since then embedded hosts can be found in most televisions, set-top boxes and many printers.
In 2012, the USB-IF published a new specification for embedded hosts which is part of the OTG specification. The Embedded Host v2.0 Supplement and compliance procedure can be downloaded from the USB-IF OTG webpage at http://www.usb.org/developers/onthego/ .
This is a notice that in June, 2013, the USB-IF will begin requiring all embedded hosts to comply with the v2.0 Emedded Host Supplement.
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Engineering and Technical Services Group