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List:       linux1394-user
Subject:    Re: onchip loopback test & dongle loopback test
From:       Stefan Richter <stefanr () s5r6 ! in-berlin ! de>
Date:       2011-01-29 0:11:14
Message-ID: 20110129011114.72a42ec1 () stein
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On Jan 25 Dan Dennedy wrote:
> I forwarded it to the mailing in case anyone there is interested
[...]
> http://www.via.com.tw/en/products/peripherals/1394/vt6308ps/
> in particular, see pages 40 (34) and 41 (35)
> ftp://ftp.vtbridge.org/Docs/1394/DS_VT6308PS_100_CCPL.pdf
> 
> DS_VT6308PS_100_CCPL.pdf shows the wiring connection for six wire connectors.
> This uses the XTP"BIAS" and XCPS connections, which the four wire
> (data only) system does not use.
> I am not yet conversant with the firewire protocol, but already can
> see that the four wire connectors are unable to use these other two
> wires to detect the presence of a device (which is definitely
> according to this info, what the XTPBIAS connection is used for.
> Two wires (XTPBP and XTPBM) which are also used in the 4 wire
> connection, can be used to detect a device.
> 
> So obviously problems could occur if a four wire connection is used,
> when software is expecting to be able to confirm device presence by
> using a six wire protocol. Not sure how likely this is to happen.

Hi Alasdair,

the bus power pair plays no role in detection whether a PHY port is
connected or not.  Port connection status is sensed via the TPA and TPB
pairs only.  VT6308's XCPS pin is surely only this chip's means to drive
the PS and PF bits in the PHY register 0 and 5.

IOW there is no difference between 4- and 6-wire connections WRT port
connection status ( = presence of a device) detection, neither for
hardware nor for software.
-- 
Stefan Richter
-=====-==-== ---= ===-=
http://arcgraph.de/sr/

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