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Basys 3 speed?


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I'm brand new to this so forgive me if this is a super basic question. I'm trying to follow the abacus example video, but I get stuck right away when choosing the part for the project. I have a Basys 3, looks like rev D, and I need to pick a speed. It looks like that should be part of the fourth number on the main chip, but I don't have one. There's just a big blank space where it should be. Just for completeness, what I see is:






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I don't think that you should have to apologize for not being able to figure out what speed grade the particular part is on your board... it should be more obvious. Especially since this information is required to create a design for the board.

The (partial) answer to your question lies in Figure 6-4 on ug475_7Series_Pkg_Pinout.pdf available in the Xilinx Documentation Navigator installed with Vivado.

The top number is the Device Type: XC7A35T
The second row are the Package/Data code: CPG236 though frankly, I'm not sure how to separate the Date Code and Package
The 3rd row is the Lot Code

and below that is a line with the Speed Grade and Operating Temperature Code. Likely, this is a 1C for the slowest speed grade and Commercial temperature operating range. If that information is missing then it raises suspicions about whether the part is legitimate.

Vendors charge a premium for faster speed graded parts and these are unlikely to found on inexpensive products.

Ideally, this information is provided in the master constraints file.

I believe that Digilent does provide all of the necessary part information in its vivado-boards-master repository that you can point Vivado to when picking a board instead of a part. Of course there's the matter of identifying your board version and the Digilent keeping its repositories up to date with product runs.

I'm sure that the past months have been very difficult for board vendors finding parts to do a run and it is conceivable, not if unlikely, that a different FPGA speed grade than 1 is on your board. But sometimes you take what you can get if you want to manufacture product. Hopefully no one is buying parts on the black or grey markets, but customers have no control over where distributors get product from. Chip vendors have a big incentive to protect the 'chain of custody' for their devices as it flows down board product vendors through various intermediaries. I can't think of a valid reason for anyone removing any of the package markings except for shady interlopers.

If in doubt you can always select the lowest speed grade for FPGA tools as there's no lesser option. Few people want to pay for the higher speed grade unless they have a particular requirement to do so.

Edited by zygot
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The product store page has a Features tab that is always worth checking out, the first line should always tell exactly which FPGA part is loaded on the board. Something along the lines of "Features the Xilinx Artix-7 FPGA: XC7A35T-1CPG236C" where XC7A35T is the part number, -1 is the speed grade and CPG236 is the package, the last at the end probably tells you that it's a commercial grade fpga.

The Basys 3 Reference Manual should provide even more info than the store page. Seeing that you claim to be new to all this make sure to at least skim through it and consult parts of it later when needed. The schematic files can also be really useful in understanding what board you're working with.

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