[sdiy] Bus for digital patching of synths

[nvawter at media.mit.edu]

Ah, yes, a clever idea to exploit PCIe.

I bet for many FPGAs there is readily available code for PCIe transacations...
and it could be developed inside a standard PC until its ready for takeoff.

so, over at opencores, there are a number of them under the category  
"Prototype Board."
In particular, there is one called Audio DSP PCI Card.
http://opencores.org/project,fac2222m

I think backplanes are not terribly expensive, except for a few  
things, they're normal circuit boards.  They'll probably have many  
layers.  They sometimes have heavier copper, although I don't know if  
that's a marketing gimmick or seriously necessary.  Also, backplanes  
tend to be long, wide things, so in terms of surface area they can be  
large.  But it may be worth it since it's a long, long term  
investment.  It might be possible to start with old PC motherboards  
and "light them" with your own PC signals!??!  who knows ?

Here's a PCI board for the Spartan II:
http://opencores.org/project,pci-board

for Altera ACEX:
http://opencores.org/project,iiepci

for Spartan 6:
http://opencores.org/project,spartan6_pcie




-- 
http://diydsp.blogspot.com has wild and wonderful digital music instruments


Quoting "cheater00 ." <cheater00 at gmail.com>:

> Hi guys,
> one of the list members has pointed me to the VME Bus backplane
> format, which is apparently a popular format in industrial computers,
> and traces back to the 68000 memory interface. The bus goes up to 320
> MByte/sec which is 2.5 gigabits per sec. This is 39% faster than the
> calculated example I cite above: "on a single collision domain, there
> could be 10 monophonic modules which each have 6 inputs or outputs at
> 100 kHz at 20 bits". However, instead of monophonic, the VME 320
> caters for 16-voice polyphony, so it's obviously very powerful. Much
> older versions can be used for monophonic bus.
>
> The 16 voice polyphony example above calculates at 1831 Mb/s or 228 MB/s.
>
> VME 320 is supposed to be very expensive. VME 64 (which is 64 MB/s) is
> supposed to be much cheaper.
>
> This got me thinking. Perhaps it would be a good idea to use PCI
> express? A single "backplane" would be a computer with PCIe slots.
> Even nowadays, an older motherboard with 4 slots can be bought
> inexpensively. A slow, cheap CPU can be cooled fanlessly with a huge
> heatsink, so no issue there. Flex cable risers can be used to route to
> the modular interface, so that you can use any motherboard really. The
> CPU could do additional processing, such as automation or signal
> processing or even recording. The cost for 5 slots is:
>
> - motherboard + cpu + a niminum of ram = 100 EUR
> - heatsink = 80 EUR
> - silent PSU = 100 EUR
>
> The best thing is that it uses cheap consumer products.
>
> My worry is though whether 1. this can be used easily from a digital
> board on a synth (is there inexpensive silicon?) and 2. whether it can
> achieve latency as low as one would achieve with a per-sample TDM
> setup.
>
> If one wishes to go in that direction, though, PCIe seems to be a
> flourishing ecosystem of relatively inexpensive hardware. The
> programming model becomes very simple, and there are numerous good
> real-time operating systems.
>
> Because PCIe can be switched, there are numerous backplane products.
> Every typical PC motherboard has at least one PCIe x16 slot. This can
> be used to drive a card which then connects to a backplane with
> multiple new PCIe slots that either communicate with each other, or
> with the host board. Even a 16-voice modular needs one PCIe x1 lane
> per 10 modules. A PCIe x16 slot obviously provides 16 lanes (as the
> name suggests). So with use of some challenging electrical signalling
> we're looking at being able to use up to 160 modules with a single
> inexpensive PC "brain", or 3x more with PCIe 3.0, plus we can multiply
> by the amount of 16x slots the host motherboard provides. That is
> obviously more than enough.
>
> There are ready PCIe backplane products. One example is from Cyclone.
> It has a physical backplane with PCIe slots on it, which connects via
> a cable to a PCIe card that plugs into your motherboard:
>
> http://www.cyclone.com/images/block_diagrams/600_2703blk.gif
>
> No idea how much such backplanes cost. Given all the bitcoin rage
> nowadays, I would expect them to be used at least in some capacity.
> The thing is that a bitcoin miner setup has to have a lot of graphics
> cards crunching away at numbers, and those cards don't need any
> powerful uplinks since there's no texture and geometry data coming in,
> just a few initial algorithm parameters the first time the card is
> engaged. So they're perfectly fine with x1 slots, but want a lot of
> them. Since hardware cost is heavily at play here, the only acceptable
> solution is for this hardware to be cheap. So I reckon there must be
> someone doing something like this inexpensively.
>
> Physically, the backplanes might be pitched too tightly. They are
> built for normal PCIe cards, so right next to each other. Perhaps flex
> cable risers can be used, such as here:
> http://www.adexelec.com/pciexp.htm
>
> Cheers,
> D.
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