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Re: Re: [f-cpu] X-Bar replacement and PoC of massiv-parallel-computing,hints?

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On Wed, 10 Oct 2001 whygee@club-internet.fr wrote:

> on top of all that,  ternary coding is not suitable for CMOS.
> read some electrical/electronical books about this subject
> (i have some courses about it currently) : it is not possible
> to have a third stable electrical level in complementary
> process.

Hmmh, If we cannot use 4b3t, because ternary logic with CMOS is
impossible, what are the args against a highspeed serial bus with 2 wires?

On every lecture about hf-technology or highspeed-data-transmissions you
find a lot of problems with wider bus-topologies and the problems with
"uebersprechen" and capacity on bus will increase if number of lines and
frequency increase, and we want use a very wide bus aka x-bar...

You know about impulses -> system -> reaction chain?

> >> 2-wired bus with +high, low and -high levels are very fast, because we
> >> have signals like this:
> >> a: +high low -high +high -high low
> >> b: -high low +high -high +high low
> >> so the sum of levels on a and b are always zero.
> so what ?

There are less interaction with noises and less iradiation.

> >> size_of_register
> >> - ---------------- * 3  => bits/1ms + overhead_of_headers
> >> 4 * (sum of EUs)
> >
> >That's 6 times the EU clock if there are 8 EUs... and if an EU runs at
> >1 GHz, your serial bus will run at 6 GHz?!

1GHz on X-Bar is more complicated than 10 GHz on a serial bus.

> we can't do that. F-CPU is meant to work at the maximum clock speed
> already. The logic behind that is : if one part of the device runs faster
> than the rest, why can't the others run faster ? Furthermore, having

There are advantages, IMHO:
- - more robustness than x-bar against noises and iradiation
- - less logiccells
- - less routing-problems
- - less floor space
- - easier to extend, if number of units wil grow or if registersize

> everything fully synchronous and with one clock only is so much easier
> to debug and understand.

The serial protocol can be used to synchronize units too.
To understand the protocol/serial bus, you need only a timing diagramm.
To debug a serial bus, you must only add a serial/parallel-converter or
use a logic-analyzer/protokoll-analyzer...

Also if there is no need to use a serial bus between units, it could be a
good way to interact with f-cpu, IMHO.

> >> Remember, a parallel bus is a capacity and frequency-sensitive and costs
> >> many of logic (see X-bar or Shifting-unit).
> >Buses are evil anyway, whether they have 2 lines or 200 ;)
> like evils, they are unfortunately necessary ...
> "il faut de tout pour faire un monde"...

Your/MRs opinion is not substantiated. Also remember serial bus in
Firewire, USB, Serial-ATA, Maple-Protokoll (Dreamcast) and so on...

Bye Andreas
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