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Would it be safe to say that modern FPGA, although larger, are not more complex, in terms of the bit stream that programs them? In other words, that a modern c
by angel_j 6y ago
Would it be safe to say that modern FPGA, although larger, are not more complex, in terms of the bit stream that programs them?
In other words, that a modern chip's bit stream is not more complex, only longer?
- kens 6y agoSome FPGAs such as the Xilinx 7 series support bitstream encryption, so that's a new layer of complexity. Modern FPGAs also have much more in each CLB, and have multiple types of CLBs, so the bit stream is more complex in that way. See e.g. https://www.xilinx.com/support/documentation/user_guides/ug384.pdf https://www.xilinx.com/support/documentation/user_guides/ug3... I don't know a whole lot about modern FPGA bitstreams, so I'd be interested in anyone has more details. Is the bitstream still essentially a pile of raw bits controlling things, or is there more structure inside?
- anfilt 6y agoThe bitstream is probably decrypted as it enters the chip. After that at best you might have some simple xoring at each CLB to make someone probing with needles life harder. Also making sure each data line is not on the top or bottom layer to make non-destructive access harder. At which point you going to need careful application of acid or focused ion beam ablation.
- trollied 6y agoThe encryption has been broken. You can read about it here https://news.ycombinator.com/item?id=22915831 https://news.ycombinator.com/item?id=22915831
- anfilt 6y agoI was not saying anything about that, but if you look at that paper or video you can see the bitstream is passed through an AES decryption stage before programing the logic fabric. This break found a way to read the data after that AES stage. However, I was just explaining how encryption generally works for these things. Weather or not breaks exist for some chips.
- anfilt 6y agoI would like to also add if your curious about more modern FPGA bit-streams there are these two projects which reverse-engineered bit streams for open source synthesis. https://github.com/SymbiFlow/prjxray https://github.com/SymbiFlow/prjxray https://github.com/SymbiFlow/icestorm https://github.com/SymbiFlow/icestorm
- ThrowawayR2 6y agoNot an expert but, in modern FPGAs, the CLBs are more complex, there are dedicated resources like multipliers and block RAMs scattered around, and routing resources are much more complex because of the vastly increased size.
- snvzz 6y agoYou might enjoy this document[0]. [0]: https://www.doc.ic.ac.uk/~wl/papers/survey/kuon08.pdf https://www.doc.ic.ac.uk/~wl/papers/survey/kuon08.pdf