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0 pointsaappleby5mo ago0 comments

"there's no publicly available documentation of the signal routing configuration or the bitstream format"

Both of things either have already been reverse-engineered, or are in the process of being reverse-engineered.

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The reverse engineering efforts are impressive (though as I understand it, limited to Xilinx series 7 and Cyclone V) but without robust and reliable timing data to go with the rest of the chip data, they can't give you the same level of confidence that a design will work across a range of a devices and operating conditions.

amirhirsch5mo ago

For the curious: the process of discovering the logic and route timings for an FPGA device is to use ring oscillators (three series inverters) and compare counters against a known clock. Place the inverters all over to test every LUT, and use every routing path to test each path's timing.

adwn5mo ago

> Both of things either have already been reverse-engineered, or are in the process of being reverse-engineered.

Please provide a source for this claim. Yosys, for example, can't route [1] designs even for Xilinx 7-series devices, and that architecture has been introduced 15 years ago.

[1] Not to be confused with synthesis, mapping, or placing, all of which come earlier in the flow, and for all of which sufficient information is public available.

robinsonb55mo ago

Yosys doesn't do place-and-route - typically that part would be handled by nextpnr, and there's an experimental fork of that for Xilinx series 7 devices: https://github.com/openXC7/ (full toolchain)

It works well enough to build a working litex RISC-V SOC capable of running Linux, for the QMTech Kintex-7 325T board.

I don't think the Cyclone V project has got as far, but I could be wrong. (It kind of slipped off my radar after I realised I was spending way too much time on Discord and purged all but a very few servers to reduce my distractions.)

j / k navigate · click thread line to collapse

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robinsonb55mo ago

amirhirsch5mo ago

adwn5mo ago

> Both of things either have already been reverse-engineered, or are in the process of being reverse-engineered.

Please provide a source for this claim. Yosys, for example, can't route [1] designs even for Xilinx 7-series devices, and that architecture has been introduced 15 years ago.

[1] Not to be confused with synthesis, mapping, or placing, all of which come earlier in the flow, and for all of which sufficient information is public available.

robinsonb55mo ago

Yosys doesn't do place-and-route - typically that part would be handled by nextpnr, and there's an experimental fork of that for Xilinx series 7 devices: https://github.com/openXC7/ (full toolchain)

It works well enough to build a working litex RISC-V SOC capable of running Linux, for the QMTech Kintex-7 325T board.

j / k navigate · click thread line to collapse