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Re: [Discuss-gnuradio] Speaking in Favor of Firewire

From: Jeff Rush
Subject: Re: [Discuss-gnuradio] Speaking in Favor of Firewire
Date: Sat, 11 Jan 2003 01:16:52 -0600
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I'd like to speak in favor of using Firewire versus USB 2.0. My background is systems software with some digital electronics engineering -- complete novice where RF is concerned. I have not yet built a Firewire board, so my claims are based on tech lit, not experience. I plan to do so, when I am gainfully employed again... ;-(

Firewire is cool because:

[*] current speed is 400 megabits per second, with standards for up to
    3.2 gigabits per second when switching from wire to fiberoptic,

[*] supports bandwidth allocation and isochronous streaming, with a
    transmission frequency of down to 125 usec per block of 1KB.

[*] can be daisy-chained, so multiple radios could be strung together
    say for a phased-antenna setup or just protocol/freq conversion,

[*] data stream doesn't have to go thru the PC but can be picked up
    by other Firewire devices on the same cable; the PC then becomes
    a symphony conductor directing data streams among radio units,

[*] multiple listeners, so that a raw data stream from a receiver
    can be processed/filtered by multiple CPU devices, to extract
    features/frequency bands,

[*] both power (8 to 40 volts, 1.5 A max) and data go over same cable,

[*] supports fiberoptic cabling, which may be useful in noise reduction
    and placing the conversion electronics close to antenna fixtures
    (although you lose the power option when using fiberoptics),

[*] the leading chipsets are available on the web from TI in cheap
    ($5-15), small quantities for home/hobbyists via a relationship
    btw TI and Digikey,

[*] single chip solutions are available from TI; used to be you had to
    use a PHY chip and a LINK chip but not anymore,

[*] on the PC side, drivers come with Windows, MacOS and Linux, so
    everyone can play,

[*] has a simple, memory-mapped read-write register architecture (up
    to 256 terabytes per device), for controlling devices (tuning,
    filtering, etc.); no need to invent another protocol or packet

[*] self-configuring addresses, no need for switches or IP assignment,

Note: The standard firewire cable is good for 400 Mbps over 4.5 meters
      using 28 AWG wire.  Cables with 24 AWG can run up to 14 meters
      and several companies (NEC, Sony) have announced plastic optical
      fiber solutions that allow for lengths of up 100 meters.

Re protocol stacks on the -device- side; many of the chips I've seen don't require a lot of protocol work as they do much of it internally; you just shove bits thru. However some kind of CPU will be required but if chosen carefully, can be something uLinux-based, meaning the protocol stack is free and accessible, which is part of the charter of GNU Radio.

-Jeff Rush

Some References:

Ettus, Matt wrote:

-----Original Message-----
From: Daniel Rogers [mailto:address@hidden

One need only to connect this chip to an existing data bus with enough capacity (12bits * 40Msps = 480 Mbps, at least). This would mean (in my experience) pretty much either pci, gigabit ethernet, or Firewire-2.

I'm actually working on a high end syste, like this.  It is USB2 based,
instead of firewire.  It has 4 analog inputs (10 bits, 60 MS/s), 4 analog
outputs (12 bits, 120 MS/s).  We're about to get prototype boards made, and
it will eventually be sold in the $200 to $400 range, depending on
configuration.  Hopefully by late summer it will be available.

There is where I have gotten stuck. I haven't been able to find a single chip firewire-2 solution, which would be ideal. It would require less configuration that ethernet, and I believe that Firewire-2 can provide enough power to power the ADC without an external powersuppy.

IMHO, Firewire is a bad idea because you need very heavy embedded stacks,
and those don't come free.  USB2 is much simpler.


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