Memory size exceeds maximum allowed bits 4096

[mihelog]

Hello everyone!

Using OpenRoad-flow-scripts I am trying to synthesize a module that contains memory inside it:

reg loaded_data_mem [0:TOTAL_BITS-1]; // Memory array indexed by bit position

The size of the above is 12471936 bits.

Both for asap7 and nangate45 I get the same error on the OPT_CLEAN pass:

Memories found in the design:
Rows | Width | Bits | Module | Instances

12471936 | 1 | 0 | hdc_classifier |

ERROR: Synthesized memory size exceeds maximum allowed bits 4096

Is there a way to remove this memory size limit? Does it come from the technology files?

Apologies if this has been asked before. I searched and could not find the answer. Thank you in advance.

[QuantamHD]

I don't see that error anywhere in the Yosys codebase can you check what version of ORFS you are using?

Also what version of Yosys is checked out.
cd tools/yosys && git rev-parse HEAD

[mihelog]

For sure. This is the output:

aaa5347494801e9e3870b31387da59da24233f76

[maliberty]

See scripts/mem_dump.py SYNTH_MEMORY_MAX_BITS. You really should use a memory compiler for a ram that large

[mihelog]

Thank you so much. I have used some proprietary memory compilers. Is there an easy way to do in OpenRoad flow scripts or is it about using an external one and integrating a black box?

[mihelog]

Btw I'm not sure if it matters, but I couldn't find that definition in script/mem_dump.py but I did find it in config.mk in some designs so I added it there for mine:
export SYNTH_MEMORY_MAX_BITS ?=

[maliberty]

Generally they are provided by the foundry. What PDK are you using?

[mihelog]

I was using the embedded asap7 library just for estimations. Not ready to fabricate by any means. I haven't found an SRAM generator for asap7.

[maliberty]

For placeholders you can use https://github.com/The-OpenROAD-Project/FakeRAM2.0 or @oharboe can tell you about his methodology.

[mihelog]

Thanks for the pointer. Quite interesting.

[maliberty]

They are generally integrated as a black box with a LEF and Liberty

[mihelog]

Got it! Makes sense.