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0 pointswanderingjew5mo ago0 comments

> On the technical side, somewhat more recent FPGA 'placement' algorithms used a simulated annealing algorithm, while what you didn't isn't about placement, that approach could posisbly help with 'net cross-over reduction' type of passes, and maybe help with designs where you can do port swap / pin swap.

Yeah, that was the first step in creating the netlist for the backplane. Simulated annealing on the 8196 nets. TO BE FAIR, this would be a lot easier to route if I didn't explicitly want each of the 16 cards to be identical, but I think that's the most cost-effective way to do it.

As far as an FPGA.... I don't know if I see the point. The nodes in the original CM-1 were basically _only_ ALUs. Very little processing power. The CM-5 was a little better, but this entire thing is batshit crazy. I might as well go for four thousand individually programmable cores. Like, what even is a MISD computer? I have no idea, so lets build one. See what it can actually do.

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vrinsd5mo ago

If you're open to technical feedback your last comment, I've worked on these kinds of systems, have architected and built things even far "weirder" and these products have shipped and out in the real world, in silicon, in FPGAs and things between.

The reason an FPGA is a more suitable platform is you can translate "physical effort of making PCBs" into "creating a design in an infinitely re-programmable platform" and change your design as needed to your hearts content.

In fact, the original design of RISC-V included a bus called 'TileLink' to enable 'Many core' arrays of RISC-V processors.

Translation: You can pare-down open-source RISC-V cores and use TileLink and emulate CM or build something more complex as you see fit since that was built into the original open-source RISC-V specs.

FPGAs are their own joy and pain for sure and it's not as "cool" to re-program a blackbox on a PCB as it might be to make your own thing, so all depends on your goals.

actionfromafar5mo ago

I dunno. Each of these physical processors have 8 kilobytes SRAM and 62 kilobytes of some kind of flash or something. Multiply by 4096, wouldn't that be one hell of an FPGA?

vrinsd5mo ago

If you look at modern FPGAs they have prodigous amounts of on-chip memories (BRAMs and URAM in Xilinx speak).

You can buy Xilinx FPGAs on PCIe cards that could easily handle THOUSANDS of RISC-V cores.

Almost all FPGA dev boards include DDR memory so you could also put code there if you needed to.

actionfromafar5mo ago

Interesting, thanks.

j / k navigate · click thread line to collapse

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vrinsd5mo ago

In fact, the original design of RISC-V included a bus called 'TileLink' to enable 'Many core' arrays of RISC-V processors.

Translation: You can pare-down open-source RISC-V cores and use TileLink and emulate CM or build something more complex as you see fit since that was built into the original open-source RISC-V specs.

FPGAs are their own joy and pain for sure and it's not as "cool" to re-program a blackbox on a PCB as it might be to make your own thing, so all depends on your goals.

actionfromafar5mo ago

I dunno. Each of these physical processors have 8 kilobytes SRAM and 62 kilobytes of some kind of flash or something. Multiply by 4096, wouldn't that be one hell of an FPGA?

vrinsd5mo ago

If you look at modern FPGAs they have prodigous amounts of on-chip memories (BRAMs and URAM in Xilinx speak).

You can buy Xilinx FPGAs on PCIe cards that could easily handle THOUSANDS of RISC-V cores.

Almost all FPGA dev boards include DDR memory so you could also put code there if you needed to.

actionfromafar5mo ago

Interesting, thanks.

j / k navigate · click thread line to collapse