How does xp determine 1394 ISO data rate to device.

[Guest]

Hello.

1394 device's capable data rates are S100, S200, S400 and S800.
Each devices has multiple layer, and each layer's capable data rate
can be different.

For example, My product(Digital Camcorder) has PHY, LINK and 61883 Layer
and each layer's capable iso data rate is following.
- PHY : 400Mbps
- LINK : 400Mbps
- 61883 : 100Mbps (It complemented on IMPR(Input Master Plug Register))

When device is connected to PC(xp), PC read the three speed register.
But, windows xp(without no servicepack) send ISO data to device at 400Mbps

I expected windows xp will determine minimum data rate what device's layerhas.

So I did same test on window xp with servicepack 1, and 2
then, PC use 100Mbps.

Finally, my question is following.

1. Why windows xp(without any servicepack) use 400Mpbs to device witch has
100Mbps setting on 61883 IMPR?

2. What is the xp's rule to determine ISO data rate to device.

3. How about win98, win me, win2000 ?

 

[Treeman]

Hello.

1394 device's capable data rates are S100, S200, S400 and S800.
Each devices has multiple layer, and each layer's capable data rate can
be different.

Hi Smartman,
The only KB article on data rates from Microsoft I could find is one
about XP.
'A digital camera that uses S400 speed is an example of such a device.'
(http://support.microsoft.com/kb/885222)
It kind of gives a before and after overview of defaults.
Maybe of some help.
Best,
Treeman