Why does SPD on DAS require high speed USB 2.0 ports?

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The Release Notes for Device Access Server (DAS) version 3.3.1. (The most recent version) state in the notes the following:...

Please note:
1. For SPD a device connection is only established if the miniWiggler is using a high speed USB 2.0 port, hub and quality cables. JTAG and DAP are not affected by this restriction.



Does anybody know why USB 2.0 is really required for SPD?
Shouldn't it be backwards compatible from USB 2.0 to USB 1.x?

I hope somebody can explain why a device connection is only established if the miniWiggler is using a high speed USB 2.0, and not under USB 1.x

Best regards, Johan.
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2 Replies
Albrecht
Employee
Employee
Hi Johan,

the technical background is that we need to emulate the SPD protocol with the FTDI chip on the miniWiggler.
This emulation requires an oversampling without gaps.
If the USB connection is slow, there will be gaps because the host is too slow providing the commands.

-- Albrecht
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Dear Albrecht,

Thanks for your reply. That indeed explains it all. Good to know.

Best regards from the Netherlands, Johan.

P.S. For your information why I wanted to know this: The Virtual Machines I use (VMware) by default generate a USB 1.x subsystem. So I need to upgrade my Virtual Machines towards USB 2.0 in order to make full use of the debug capabilities... Luckily this software upgrading is easier than upgrading real hardware USB ports... 🙂
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