David Brown <firstname.lastname@example.org> writes:
> needed, I don't think there are FPGA's big enough on the market. Had
It's possible to build build a clos style crossbar out of smaller
FPGA's, but you "waste" a lot of serdes links for switch expansion, e.g.
in the figure below each switch element could be a 4x4 FPGA which is
interconnected to form a 8x8 switch:
.sig removed by request.
Reply by GaborSzakacs●April 23, 20132013-04-23
David Brown wrote:
> On 08/04/13 17:58, email@example.com wrote:
>> You might consider to use 16 external receivers and 16 external
>> transmitters and use the FPGA to mux the databuses. There are some
>> Rx/Tx that support DDR on the databuses, so this will get you 16pins
>> per Rx/TX (12b+HD+VD+DE+Clk) x 32 = 512 Pins Total. There are at
>> least low cost Cyclone IV that have so many IOs (CE30/CE40).
>> But I have not checked if this DDR-style Rx/Tx are also available for
>> HDMI1.4 and how this solution compares to this crosspoint switches.
> Unfortunately, the numbers are bigger than that. HDMI receivers and
> transmitters that I have seen have SDR on the databus, but for HDMI1.4
> that would be 36 lines at 340 Mbps. So for 16 channels in and 16
> channels out, that would be 36*16*2 = 1152 pins, all running at 340
> Mbps. That's a lot of pins - and even if we got an FPGA big enough,
> designing such a board and getting matched lengths on all the lines
> needed would be a serious effort.
> The crosspoint switches mentioned by another poster are one likely
> choice. The other realistic architecture is to use large numbers of
> 4-to-1 HDMI multiplexers.
Probably not a good solution at 340 Mbps, but when you have a large
parallel bus and need a number of these in a crossbar, you can split
the bus into bit slices and handle them in separate smaller and
much cheaper devices. Generally, using a very high pin-count FPGA
with very little logic is a big waste of silicon. For something as
regular in structure as a parallel-bus crossbar, splitting the bus
into slices can reduce the silicon area by using a number of FPGA's
programmed identically each handling the same slice from every port
on the crossbar. The problem at very high speeds would be part to
part skew. You can control voltage and temperature among the parts,
but you're at the mercy of the manufacturer for process variation.
Reply by Morten Leikvoll●April 23, 20132013-04-23
Not a fgpa solution, but have a look at analog devices ADN4605 and its
likes.. A few of those and you got full matrix of even more ports.
Reply by ●April 23, 20132013-04-23
Arrow shows 5SGXEB6R2F40C3N in stock @ $9,092.00 ea (min/multiple = 1).
Very likely not cost effective...
Reply by David Brown●April 23, 20132013-04-23
On 23/04/13 01:36, firstname.lastname@example.org wrote:
> This is not a question of practical/economic consideration, per your
> original statement.
> Altera Stratix V GX B series has 66 full-duplex, 14.1 Gbps
> transceivers with independent Rx/Tx PLLs (e.g. 66 inputs, 66
> outputs), and 490K-952K logic elements for an x-bar.
I didn't realise the Rx and Tx sides of the transceivers could operate
independently - that's why I dismissed these as too small.
> Probably not cost effective, but technically feasible.
Well, if it is possible to buy these devices, then I agree.
Reply by ●April 22, 20132013-04-22
This is not a question of practical/economic consideration, per your original statement.
Altera Stratix V GX B series has 66 full-duplex, 14.1 Gbps transceivers with independent Rx/Tx PLLs (e.g. 66 inputs, 66 outputs), and 490K-952K logic elements for an x-bar.
Probably not cost effective, but technically feasible.
Reply by David Brown●April 22, 20132013-04-22
On 22/04/13 20:27, email@example.com wrote:
> OK, it's an economic issue, not a technical issue.
I think it's a bit of both - when looking at the numbers of I/O's
needed, I don't think there are FPGA's big enough on the market. Had it
been 8x8 rather than 16x16, it would perhaps have been an economic
issue. But with 16x16, we would need 64 inputs at 3.4 Gpbs and 64
outputs at 3.4 Gpbs - I don't think there are any FPGAs that have that
many high-speed channels. And if we use external encoder/decoder chips,
the speeds per line are lower but we would need far more of them.
Certainly in principle an FPGA can be used for an HDMI cross-point
switch, but it seems that it is not a practical solution for such a big
Reply by ●April 22, 20132013-04-22
OK, it's an economic issue, not a technical issue.
Reply by David Brown●April 21, 20132013-04-21
On 20/04/13 00:15, firstname.lastname@example.org wrote:
> There are two approaches to doing this in an FPGA. The OP is looking
> at one that would bring the TMDS and clock lines directly to the FPGA
> (assuming appropriate equalization / level shift / drivers on PCB).
> An FPGA cannot provide a simple crosspoint function internally, thus
> one would have to put 16 instances of HDMI RX and 16 instances of
> HDMI TX cores in the device and create the crosspoint in the fabric.
> My personal opinion is that the number of cores, the clocking
> resources, and logic required would make this a futile exercise.
> The second approach is mentioned by Thomas already. This at least
> keeps the HDMI PHY and RX/TX stack out of the FPGA, but will require
> quite a bit of IO depending on OP needs.
> To attempt either will require a large and costly FPGA, I think the
> OP will find the crosspoints cheaper in the end.
Yes, that's pretty much the same conclusion as we came to (after you and
another off-list poster suggested crosspoints) - and we are now using
such a crosspoint switch on the board.
Thanks to all for their suggestions.
Reply by ●April 19, 20132013-04-19
There are two approaches to doing this in an FPGA. The OP is looking at one=
that would bring the TMDS and clock lines directly to the FPGA (assuming a=
ppropriate equalization / level shift / drivers on PCB). An FPGA cannot pro=
vide a simple crosspoint function internally, thus one would have to put 16=
instances of HDMI RX and 16 instances of HDMI TX cores in the device and c=
reate the crosspoint in the fabric. My personal opinion is that the number =
of cores, the clocking resources, and logic required would make this a futi=
The second approach is mentioned by Thomas already. This at least keeps the=
HDMI PHY and RX/TX stack out of the FPGA, but will require quite a bit of =
IO depending on OP needs.=20
To attempt either will require a large and costly FPGA, I think the OP will=
find the crosspoints cheaper in the end.