|Originally posted by imws:
Just a quick aside here, 29 Mbs read 29 Megabits per second, I'm confused, why does Rick think this will be a problem to interface with a PC?
Getting a signal with this kind of bandwidth into a computer should not be problem since there are ethernet cards out there for the PCI bus that are rated at 1Gbs read 1 Gigabit per second. Bits are bits as they say.
You do have a valid point.
Like I said, I have some but not a lot of PC experience. Although I have never seen 1Gb Ethernet. I have seen 100Mb Ethernet (EtherFAST). EtherFAST might be fast enough. Just remember that 100Mb is the flat rate. It doesn't include packet overhead that must be fit into same bandwidth. It does seem to me that there sould be plenty of room to fit 29mbs into a 100Mbs channel even with overhead.
A custom protocol would have to be devised, since Ethernet uses HDLC and MAC hardware interface protocols (FYI, if you are interested you can look up the standard ISO communications protocol stack model). This would not nearly be as difficult as Firewire would be. Still you need an intelligent controller to handle upper level protocols betwwen the 29Mbs stream and the ethernet stream.
The Ethernet controllers you plug into your PC already handle the lower level protocols so what ever you hook on the other side of the cable, has to talk the same language. You just can't shove bits down the cable and expect the controller to intelligently process it. The controllers are optimized to a set of standards that govern the data flow across the cable that has to handle a bunch of things (like collision detection and retransmision, etc. Ethernet IS a bus based protocol even if the electrical configuration is a star [hub based] based network).
All in all, it might be easier than an FPGA based system but my expertise makes me lean towards the FPGA on a PCI card.
Firewire is not a simple system even though it gives the appearance of being simple (An endearing attribute of firewire and I think points out some of it's greatest power). Yes the cable is only 6 or 4 wire, but the controllers at the end of the cable are very complex. Every time you unplug or plug in a firewire device into a Firewire network, everything on the entire bus resets itself, the bus ID's are completely re-configured, and the bus data traffic is re-started (even if it is only two devices and one cable). Theoretically you could be recording on your Firewire VCR a program from your Firewire tuner, while listening music from your Firewire digital radio reciever and if you plugged in your digital video camara, the reconfiguration would occur WITHOUT interruption of any of these other operations. That is the power of Firewire. And it is not an easy protocol to implement to achieve this. You could argue to implement a subset of the protocols, but both controllers on each end of the cable would have to know this. That would be difficult with an off the shelf firewire card you would plug into your computer.
As far as recording the RGB right off of the RGBHV output of a tuner, it is certainly possible. I'll do a quick calcualtion:
1080ix1920x60fps = 540x1920x60fps = 62,208,000bps
Not insane, but clearly more bandwidth is needed. A high quality ADC is needed (actually three), but simple compression can be implemented by taking advantage that color doesn't need the same bandwidth as luminance so I could see it being possible to get to 29Mbs pretty easily (Maybe that's what GI did?).
Of course, I have heard that it is exactly this kind of a recorder that makes the MPAA shake in their shoes. Seems to be a big reason why MPAA wants encryption through the entire HD signal chain so engineers like me can't get at the raw data (like we couldn't just hack into the projection system!).
[This message has been edited by wirehead_rick (edited 12-23-2000).]