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A High-Performance Open Source Oscilloscope: development log & future ideas

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asmi:

--- Quote from: nctnico on November 19, 2020, 03:01:06 pm ---For a moment assume the $4k for the Cyclone 10 license drops to 0. Are there any technical problems with the Cyclone 10 FPGAs? The Kintex device you are proposing is about 3 times more expensive (up to 10 times when comparing Digikey prices).
--- End quote ---
I'm not interested in discussing spherical horses in the vacuum. I prefer practical approach. And it tells me for 4k$ a year I can buy quite a bit of Kintex devices, which can be used with free tools. Besides even top of the line GX device fall short of what 325T offers, while being priced similarly to 325T from China, with it's relatively obtainable license. If we stick to free versions of tools, 160T offers quite a bit of resources - up to 8 12.5 Gbps MGTs, same 64/72bit 933 DDR3 interface, up to x8 PCIE-express 2 link (PCIE Gen 3 is possible, but you have to roll your own, or buy commercial IP) and all other goodies of 7 series family.


--- Quote from: nctnico on November 19, 2020, 03:01:06 pm ---Even with the $4k subscription it doesn't take selling a lot of boards to break even.

--- End quote ---
Did you forget the part that it's an open source project? That means tools must be free.

Fungus:

--- Quote from: tom66 on November 19, 2020, 08:20:25 am ---I did consider this when I first embarked on the project, but the reverse-engineering exercise would be very significant.

--- End quote ---

And the manufacturer could decide to stop production of that model at any moment and you'll be back to square one.

nctnico:

--- Quote from: asmi on November 19, 2020, 03:18:44 pm ---Did you forget the part that it's an open source project? That means tools must be free.

--- End quote ---
Some tradeoff needs to be made here. If requiring free tools increases the price of each unit with several hundreds of US dollars then that will be an issue for adoption of the platform in general. For example: one of my customers has invested nearly 20k euro in tooling to be able to work on an open source project. Something else to consider is risk versus free tools. For example: the commercial PCB package I use can do impedance and cross-talk simulation of a PCB and has extensive DRC checks for high speed designs. Free tools like Kicad are not that advanced so they need more time for manual checking and/or pose a higher risk of an error in the board design which needs an expensive re-spin. At some point software which costs several $k is well worth it just from a risk management point of view. Developing hardware is expensive. IIRC I have sunk about 3k euro in my own USB oscilloscope project (which wasn't a waste even though I stopped the project).

Anyway,  I think your suggestion for the Kintex 70T (XC7K70T) is a very good one. I have overlooked that one. Price wise it seems to be on par with the Cyclone 10CX085 and it can do the job as well.

tom66:
The Zynq 7014S has 40k LUTs + ARM processor + hard DDR controller fabric.  1 unit starting from $89 USD.

IMO that wins over the 65k LUTs + no hardcore CPU + no DDR3 controller in the Kintex 70T -- and in my experience the MIG eats up easily 20% of the logic area for just a single channel DDR3 controller, I'm not convinced that would be a worthwhile trade off here. By the time you've implemented everything that the Zynq gives you "for free" (including 256KB of fast on-chip RAM) you're stepping up several grades of 'pure FPGA' to get there.
 

tom66:
The present oscilloscope fits in ~20% of the logic area of the 7014S.  That's including a System ILA which uses about 10% of logic area. I imagine the 'render engine' would use about 10-15% of logic area if implemented on the FPGA fabric.  We're not constrained by the fabric capacity right now - but more by the speed of the logic.  And a lot of that is down to experience in timing optimisation which is an area I have a lot to learn about.

Moving up a speed grade may be more beneficial than moving to a bigger device.

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