looking for details on hierarchical flow

[Cronus-38]

Hello, I'm trying to find additional documentation on a hierarchical flow (i.e. bottom-up flow). I want to run a sub-block through the Openroad flow, then take the resulting GDSII and use it as-is (via manual placement) within my top-level run. I found the BLOCKS variable, and I see that if it's set then the flow will look for the sub-block files:

ifdef BLOCKS
ifeq ($(MAKELEVEL),0)
  $(info [INFO][FLOW] Invoked hierarchical flow.)
  $(foreach block,$(BLOCKS),$(info Block ${block} needs to be hardened.))
endif
  $(foreach block,$(BLOCKS),$(eval BLOCK_LEFS += ./results/$(PLATFORM)/$(DESIGN_NICKNAME)_$(block)/$(FLOW_VARIANT)/${block}.lef))
  $(foreach block,$(BLOCKS),$(eval BLOCK_LIBS += ./results/$(PLATFORM)/$(DESIGN_NICKNAME)_$(block)/$(FLOW_VARIANT)/${block}.lib))
  $(foreach block,$(BLOCKS),$(eval BLOCK_GDS += ./results/$(PLATFORM)/$(DESIGN_NICKNAME)_$(block)/$(FLOW_VARIANT)/6_final.gds))
  $(foreach block,$(BLOCKS),$(eval BLOCK_CDL += ./results/$(PLATFORM)/$(DESIGN_NICKNAME)_$(block)/$(FLOW_VARIANT)/6_final.cdl))
  $(foreach block,$(BLOCKS),$(eval BLOCK_LOG_FOLDERS += ./logs/$(PLATFORM)/$(DESIGN_NICKNAME)_$(block)/$(FLOW_VARIANT)/))

But I don't understand the function of the MAKELEVEL variable, and when I run with BLOCKS=my_sub-block it tells me that the block needs to be hardened. Clearly I'm not doing things right.

Thanks,
Cronus

[rovinski]

I'm not intimately familiar with the hierarchical flow but just as a note, MAKELEVEL is a makefile built-in variable which changes automatically when Make invokes another Make. So MAKELEVEL is 0 when the top-most block is called, then when it calls Make on the children, each one will have MAKELEVEL as 1, if any of those invocations called Make again, MAKELEVEL would be 2, and so on.

So ifeq ($(MAKELEVEL),0) executes that section only if it's the top-most Make invocation (i.e. you're calling it on the design top-level). I believe the strategy is to call it on the top-level, and then Make will automatically recurse through the child blocks and execute Make on those, exporting them, and then incorporating them into the hierarchy above them.

One of the issues you might see is that Make automatically passes its environment from the parent to the child. There's lots of cases where that's helpful, but it's not helpful here. So there are some steps taken to ensure the environment is reset when it hands it to a child.

At least, that's what I understand. I haven't run it myself.

[maliberty]

See https://github.com/The-OpenROAD-Project/OpenROAD-flow-scripts/blob/master/flow/designs/asap7/aes-block/config.mk for an example that you can also run.