Technology Porting Instructions about dffram HOT 3 OPEN

Hey Leo,

With the merging of #104, we've enabled this.

The general idea is, you'd want to replicate the file structure in platforms/sky130A for your PDK.

We only have two hard requirements:

• There must be a 1:1 mapping for the cells
• The instance names for the cells must be the same as in https://github.com/Cloud-V/DFFRAM/blob/main/platforms/sky130A/sky130_fd_sc_hd/_building_blocks/ram/model.v .

Everything else is either configurable or of no consequence: we don't care about the ports of the cells, for example, and the names of the modules can be defined in https://github.com/Cloud-V/DFFRAM/blob/main/platforms/sky130A/sky130_fd_sc_hd/_building_blocks/ram/config.yml.

If you want to use dffram.py, your PDK must be supported by Open_PDKs, otherwise, you'd have to do some steps manually.

This info should be enough to start but we're planning to provide more thorough documentation in the very near future, god-willing.

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Thanks I will look into these instructions and give it a try.

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I was wondering if you have any experience with porting to a technology without 1:1 logic mapping. I'm in the process of doing so, and it's mostly just things like not having a particular AND gate with the exact amount of inverted inputs. It's simple enough to manually add in an inverter and write extra code for placeram, but I'm encountering a bigger issue in that yosys is deciding to optimize logic away, resulting in things like entire decoders going away.

For my case, I'm running the 32x32 regfile_2R1W and am only seeing a single DEC5x32 in my synthesized netlist:

UDBLVT20_BUF_S_2 \DEC2.D1.ABUF[0]  (
UDBLVT20_BUF_S_2 \DEC2.D1.ABUF[1]  (
UDBLVT20_BUF_S_2 \DEC2.D1.ABUF[2]  (
UDBLVT20_NR4B_2 \DEC2.D1.AND0  (

So no DEC1 or DEC0 instances. This causes problems later with the d2a function and also placeram accesses the returned array with hardcoded index elements since it expects an array of [2:0].

Do you have any experience with Yosys optimizing logic out? I've tried expanding out the synth command in the yosys script as shown in the documentation:

http://www.clifford.at/yosys/cmd_synth.html

and removing all the opt_* steps, but am running into an issue when it tries to use proc because that's a namespace collision with a tcl command.

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