Electronics > FPGA

Reverse engineering Anlogic AL3_10 FPGA

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pcprogrammer:
A quick look at the settings bits and the block connections showed me that the global clocks are not used for some reason. That certainly explains the missing 3000 settings bits |O

So more testing of the gate level verilog generation is needed to see if I can solve this. No need to test the bit stream I have now in the actual scope, because without clocks it will not work.

Edit: It was a case of case :palm: I used "GCLK" in my manually assigned names and the rest used "gclk". The bit count went up with >2000, so still a bit of a difference and also the net list is longer. More work to be done 8)

Edit2: Tried the generated bit stream on the scope but somewhat expected, it did not work. When I upload the original the scope stops working during upload and needs a reset to come back up again, but it does work. With the new bit stream it does not come back after the reset. Definitely more work to be done. But I do have some ideas based on new knowledge gained.

pcprogrammer:
"What a mistaka to maka"  :o

I found out today that I forgot to cater for the bidirectional pins. I'm handling input and output pins but am not making the needed connections for the bidirectional pins, and these are needed for the interface with the MCU :palm:

As another experiment I changed the code to just use the SLICE macros because these can represent all the logic made with one block and is easier then creating the LUT macros, and the resulting output did compile in the IDE, but still no dice on the scope. It was also ~2500 setting bits less then the original. So I started looking at the net list, block list and setup list again and noticed that the bidirectional pins had changed into output pins. |O

So another change of the code is needed and hopefully it will then bring success.

pcprogrammer:
Aaaaaaaargh so close, but still no dice on the scope.

The net list of the newly generated bit stream now has one net more then the original, and the same goes for the block list. It has one extra block :o

Due to different routing and placing it still has less bits set, but not sure if that can cause it to not work. Routing makes up for a fair number of the used bits. But maybe some timing constraints that are not met makes it fail?

Or I made an error in the clock connections. The design uses 6 global clocks and it is still not completely clear how these clocks are connected to the global routes.

Ah well, more digging to be done.

cedric!:
I have no knowledge of Anlogic FPGA's, but there are other projects [1] that are reverse engineering FPGA bitstreams. They have projects for Lattice iCE40[2], Lattice ECP5[3], Xilinx 7[4], Xilinx Ultrascale, Ultrascale+ and UltraScale MPSoC [5]

The selling point of those projects is that they have documented the process of reverse engineering. Maybe you can (ask to) create a reverse engineering project for Anlogic FPGA's?

[1] https://f4pga.org/
[2] https://github.com/F4PGA/icestorm
[3] https://github.com/F4PGA/prjtrellis
[4] https://github.com/F4PGA/prjxray
[5] https://github.com/f4pga/prjuray




pcprogrammer:
Hi cediric!, thanks for the input, but I'm aware of these kind of projects, which are targeted to reverse engineering of the process of generating a bit stream with open source place and route software.

There is a project for the Anlogic FPGA's based on prjtrellis. (See my first post at the start of this topic) I have used that to get the listings of what a setting bit means and it was certainly helpful, but I still had to figure out a hell of a lot myself. The same applies to Gowin. It was actually the Gowin project that provided some needed information to be able to continue with my project.

A bit of a problem with these somewhat experimental projects is that they are never finished, like only fit for a single type of the manufacturers FPGA line, or not supporting specific IP like embedded ram, etc. The same is true for what I'm doing. It is just targeted at the FNIRSI 1013D FPGA bit stream.

What I'm trying to do is to reverse engineer an existing bit stream to verilog, which is a whole other ballgame. As you can read in this thread, all the data I found from the mentioned open source project for the Anlogic FPGA's is for going from verilog to a bit stream and not the other way round.

I'm actually quite close to a working result now.


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