Honored ContributorHello
I want to establish communication between two fpgas over gxb transcievers. I will use two cyclone iv gx devices. My question is can I send signals from gxb banks (pins) through lvds cable, or does it really need to be a PCIe connector? Regards
Honored ContributorDoes not have to be PCIe (or any specific connector). What is important is your signal quality across the transmission medium. For example, you can use the HSMC (Samtec) connectors like the ones on the demo boards to connect the two FPGAs. If you need cables, Samtec make flex cables that you can use. There are a number of ways to to achieve this successfully depending on your requirements.
Honored Contributorthank you very much for the reply. Board-to-board connectors are definitely out of the question. I will have two boards separated, so cable is a must .. at least 3 feet.
Do you think that with some buffer/repeaters i could guarantee the signal quality? My other question is regarding the communication protocol. Is it possible for two fpgas to exchange data over gxb ports ... in my logic i dont plan to use Nios. Thats what is bugging me. With altera megawizard i can create altgx and altgx_reconfig ... but, can i use external logic to write and read to those or does it have to be through Nios? regardsHonored ContributorWhat is your data rate? There are any number of off-the-shelf cables and connectors that might meet your needs. They range from fairly cheap to quite pricey depending on the required speed.
Honored ContributorHi
data rate i am expecting is above 1.6Gbs ...Honored ContributorWell, that narrows it down a bit, but what is the exact data rate? It sounds like GigE or USB 3.0 cables and connectors might do the job cheaply. GigE is technically not fast enough but 3 feet is pretty short and if your data rate is close to 1.6Gbps it might be OK.
Honored ContributorHi
o just googeled achievable bandwith over hdmi cables off the shelve. For 10$ i can get speeds of 10Gbs check it out http://hdmi-cables-review.toptenreviews.com/ Since this will be my first design with gxb blocks my question is, can signals coming from GXB pins (on phy level not just logic) be considered as "lvds" and i just push them through hdmi cable? regardsHonored ContributorOK, HDMI has 3 data lanes + clock and can utilize either SDR or DDR signalling. Better take all this into account when comparing the 10Gbps number to the data rate of your gx design.
As for whether buffering the gx outputs is recommended, I can't say.Honored ContributorDefenetly ... 10Gbps is too much for my design ... but is it good to know that cable will support at least 1.6Gbps
My follow up question is ... can altera components, altgx and altgx_reconfig, be controlled by external logic other then Nios? My application needs speed ... and Nios would be a bottle-neck that i would like to avoid. regardsHonored ContributorHi mirza,
You do not have to use NIOS II processors with the ALTGX component. You can configure the devices into BASIC mode and use whatever protocol you like over the cables. You will however have to be careful about the data you send over the cables. For example, the receiver CDR PLLs start in lock-to-reference mode, and then need to transition to lock-to-data mode to capture the data correctly over all process, voltage, and temperature (PVT) variations. 1.6Gbps is fairly slow though, so you will have good timing margin. Have you purchased a development kit or two? Samtec sell PCIe edge connector to SMA adapter boards. You could use those adapters to connect transceivers on a single Cyclone IV GX Development board or on a couple of boards. If you're interested in the part number, ask, and I'll post the data sheet. As far as 'standard' cables go. There is a PCIe standard for external cabling. You can use x1, x4 or x8 cables. There are also SFP+ and QSFP+ cables used for 10GbE and 40GbE. The 'direct attach' versions of these cables are copper, are under $100, and are rated to 10Gbps per lane, hence, more than fast enough for your application. Cheers, Dave
