What is the FPGA for?

[lgerbarg]

Looking at some of the MB pictures there appears to be a Xilinix Spartan FPGA. I did not notice much obvious functionality that is not accounted for by the other chips. Sometimes FPGAs are just used to implement bus routing in this sort of design, but sometimes they are used for more interesting things. I did not see anything (that I could find a datasheet on) that had an SATA interface, so I suppose that is a possibility?

Has any checked the routing on the board yet? Is the cable PHY hooked up to the FPGA? I wonder if the IO on the FPGA would be good enough to program a QPSK encoder/DOCSIS modem. I doubt it, but it would be nice.

[megazone]

I'm no EE, so I'm not much help. The 'Large' versions of my photos are 5MP - perhaps there is enough detail to answer some questions.

[lgerbarg]

I'm no EE, so I'm not much help. The 'Large' versions of my photos are 5MP - perhaps there is enough detail to answer some questions.

Motherboards are multilayer, so unless a lot of coincidences happen and the traces were all on the top layer you really need someone to electrically trace it. I do want to thank you for the photos though, they are very informative.

In my super optimistic fantasy the cable PHY is hooked up to the FPGA, which has enough IO bandwidth and open cells to implement a DOCSIS modem, which would allow the device to be software updated to Cablecard 2.0. Yes, entirely delusional, but I can dream ;-)

[sommerfeld]

In my super optimistic fantasy the cable PHY is hooked up to the FPGA, which has enough IO bandwidth and open cells to implement a DOCSIS modem, which would allow the device to be software updated to Cablecard 2.0. Yes, entirely delusional, but I can dream ;-)
IANAEE, but I think you might have left out the bit about it being hooked up so it can actually be reprogrammed in the course of a firmware upgrade downloadable from the tivo service.

[lgerbarg]

IANAEE, but I think you might have left out the bit about it being hooked up so it can actually be reprogrammed in the course of a firmware upgrade downloadable from the tivo service.

True enough. On an interesting note, Xilinx has a DOCSIS softcore that is compatible with the Spartan FPGA line.

Again, until we have some idea of what exactly is hooked up, what the Xilinix is used for, and how much free space it has this is all pie in the sky. But the system has all the right chips to do bidirectional communication and be software updated to CC 2.0. The question is if they are configured in a way that would allow it.

Edit:Not posting a full URL because it claims I have less than 5 posts. That is what I get for not posting in 3 years. Remind me to post it later. You can search for J83Annex_BModulator at Xilinx's webpage

[lgerbarg]

Okay, it looks like the USB, Ethernet, SATA and MPEG2 decoding is on the main CPU (BCM7038). So there are no major functions that would be on the FPGA.

It is physically located under the CC slots (convenient routing?), and it has just enough logic cells for a single channel DOCSIS modem with an RRC filter. If it does not need the filter it actually has almost twice as much space as it needs. At least by my read of the datasheets, I am not an FPGA expert.

Now I really, really want to know what it is used for, and how much of it is utilized. I imagine functional routing, but it is pretty likely they could have gotten away with a simpler part if that is all they intend to do with it.

[zync]

Glue logic? CC interface? There's a bunch of things that it can be.

[lgerbarg]

Glue logic? CC interface? There's a bunch of things that it can be.

Glue logic absolutely, and most likely. I doubt the Cable Card Interface, since there is a CiMAX SP2 Cablecard interface chip on the board. The only obvious feature I do not seen an explicit chip for are the actual tuners chips, but assume they are in the large tuner packages, not off board on the MB. If they actually implemented the QAM demodulator there that is great, since the QAM demodulator has to be hooked up to basically everything a DOCSIS modem would be, and it is logically the exact right block to upgrade.

Did they use an FPGA for Glue on the HDVR250-10? This design if very similiar.