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USB Help Needed
rfdes:
I have a question regarding whether it is possible to do the following:
PC (Win 10) >>> USB 2.0 Hub >>> USB 2.0 device (operating at Full Speed - 12MHz)
The device connected is set to run at Full speed but I want to 'FORCE' the PC host to communicate with the device at Low speed (1.5 MHz) only. Is there a configuration method (driver, etc.) to make this happen? I've heard some suggest to install a USB 1.x hub between the host and device but that wouldn't guarantee a low speed connection as 1.x also supports Full Speed.
I went to the USB.org website thinking there was a true 'forum' to post this question but couldn't seem to find it.
Any help offered would be appreciated.
Jim
Largo Florida USA
oPossum:
The device configures it's USB SIE (serial inteface engine) to run at full or low speed. You would have to change the firmware in the device.
magic:
... and once configured, the device signals its speed to the host which can either accept it or disregard the device altogether. There really is no other way, no means of negotiation, no undocumented tricks.
oPossum:
Even if you can change the firmware there could also be issues of class compliance and packet size. The CDC class for example requires full speed for class compliance. Low speed is limited to 8 byte packets, while full speed is 64 bytes.
SiliconWizard:
Why would you want to do that in the first place?
Yeah, the only way would be for the device to enumerate as a low-speed device only. I dont' think any hub can somehow "translate" speeds on the fly (thus making a connected device working at FS seen as a LS one by the host). I don't think any hub can otherwise make a connected device appear as a LS one only and make it function in LS mode only.
A USB device can declare itself as a LS device only to the host, but if it supports both FS and LS, I don't think there is a means for the host to require LS only. The host usually selects the highest speed both the host and the device support AFAIK.
But again, what you want to achieve is intriguing.
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