[PD] Re: BlueTooth CUI : using [comport] or [hid]

[Hans-Christoph Steiner]

On Jun 23, 2006, at 2:03 PM, Mathieu Bouchard wrote:

> On Fri, 23 Jun 2006, Hans-Christoph Steiner wrote:
>
>> As for the usage of CPU, because its a fast bitrate, it will  
>> always use a noticeable amount of CPU time.  Mouse data is another  
>> example of a high-speed data stream.
>
> old mice ran at 1200 bps. PS/2 mice might run at 9600 bps, not  
> sure. In any case it doesn't get over 1 kilobyte/sec. Each packet  
> is 3 or 5 bytes depending on the protocol. I find it likely that  
> most PS/2 mice use only a small fraction of the bandwidth, but I  
> haven't measured.


>>  IIRC, a lot of mouse pointer processing is handled by the  
>> graphics card for this reason.
>
> "Just" the display of a sprite such as an arrow. If you ever use a  
> plain VGA driver, you don't have this feature, so it has to be  
> handled software.
>
> What makes you think it's high speed? Or do you mean an example of  
> something that needs to have a low latency?

PS/2 mice can run up to 200Hz, USB HID devices up to 100Hz.  With USB  
HID mice, the data is sent every 10ms, but its not just one report,  
it can be many.  Each USB HID device is allocated 64kbps of  
bandwidth, and decent mice use it.

My Logitech MX510 sends 1 byte for buttons, 2 bytes for standard XY  
reports, and 3 bytes for hi-res XY reports (12bits per axis).  That's  
6 bytes per report.  It can send up to 64 reports per poll (every 10  
ms), so it has the ability to overwhelm the USB HID allocation many  
times over.  This is something that I have measured.

.hc

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