To USB or Not to USB


USB Certification – Important, Critical and a Great Starting Point (not an Endpoint)

USB is endpoints

That’s a Pun (which unfortunately has to be explained)

When you design a USB peripheral, like a USB mouse, it will can have as few as 2 endpoints

The mouse needs a control endpoint, for configuration. That’s Endpoint 0 (zero).

It will have 1 Interrupt endpoint.

This takes in mouse clicks, right click, left click, center click, and scrolling mouse wheel.

An interrupt endpoint must get through to the PC immediately for immediate responsiveness.

This is different from an isochronous transfer, like a video or audio transfer.  If a packet or a bit of data is lost, it’s more important the video proceed (along with audio) so the viewer can continue to enjoy the video.


The starting point is Certification.

Mr. Posner wrote a great blog on how USB Certification is essential.

It surprises me because some get certification, some do not. It also surprises me because some people, really feel this is the endpoint.  There’s nothing else.  There is more before, and much more after.  USB Certification is critical. It’s only the first part.  There’s 90% of the work left to do after certification is complete to make the product reliable.


For Synopsys getting USB certification, is a critical milestone.  But it’s one of many.  After we’ve built the IP,  we certify it, and we keep testing. We never stop.


I’d say more, but that’s for our customers.

Who actually talk to us.


Read Mick’s article here:



Somewhat technical stuff:

USB defines 4 transfer types which are:

Control – for configuration – Used in every design

Interrupt – Must be serviced immediately, like mouse clicks or keyboard signals or touch screen signals

Isochronous – For video/audio transfers.   If your drop a few bits, it’s okay, because you need to keep the video and audio going. No retrys of the data because your movie or music continues on

Bulk – For data transfers that need 100% accuracy.  This is like printing to a printer.  That print job has to have all the bits in it, or the print out won’t look right.   If a bit is lost, and can’t be recovered through error correction, the system retrys.
For fun here’s a video we did with ASMedia a year ago with our USB 3.1 Device controller.  We actually had it certified earlier this year as the first certified USB in the world (universe)


Tags USB101, USB Certification



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