Re: Powered Fireware device.

On 5 Jun, F. Heitkamp wrote:
> I have a Firewire zip drive that I bought to play around with. It can be
> powered over the firewire cable. It only seems to work like that on my
> Macintosh. Does Linux 1394 support devices powered over the firewire bus?

Firewire devices like PCs (including Macs) or hubs may deliver
power to a bus at various voltages and amperages. The 1394 spec
provides a few gradations called "power classes". The PC you
tried Linux on may provide less power to the bus than your Mac.
That would be a pure hardware issue.

On the other hand, the 1394 spec also describes software related
features for power management on 1394 buses. Two different topics
are covered by these power management features:

1. A bus manager software may activate the higher functions of
   power draining devices. The bus manager checks how much power
   is provided and how much is consumed overall by all nodes. It
   may then send "link on" packets to devices that did not power
   up themselves.
   You can check with gscanbus if the zip drive has an inactive link.
   In that case, a link-on packet may help.

2. A bus manager software may suspend and resume devices, similar
   to a PC OS that suspends and resumes internal PC hardware.

The Linux ieee1394 driver does not implement bus management
(except for isochronous resource management which is unrelated to
power management).

You can send "link on" packets e.g. with Manfred Weihs'
1394commander. The packet has this format, listed from most to
least significant bit:
2 bits = 01b
6 bits = physical ID
24 bits = 000000h
32 bits = inverse of the previous 32 bits (do not enter them in
          1394commander, they are generated automatically)

For instance, if the zip disk is the node with phy ID 0, issue a
command like "echo p 0x40000000 | 1394commander". If it had the
phy ID 3, it'd be 0x43000000. Note that even if that succeeded,
gscanbus would not update the link status until a bus reset
happens.

-- 
Stefan Richter
-=====-=-=-- -==- --=-=
http://arcgraph.de/sr/
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