sram: fakeram vs. mock SRAM

[oharboe]

No description provided.

[oharboe]

@jeffng-or FYI, will add fake sram tomorrow and write some docs. There are some snags to be fixed in bazel-orfs as well...

[oharboe]

@maliberty @jeffng-or There's no clock and "all_registers" returns 0 with fakeram. Is there something wrong with the fakeram .lib file?

Either use the standalone .tar below, or with this PR run:

bazel run //sram:top_fakeram_floorplan `pwd`/build
build/make gui_floorplan

untar no-clock-or-registers.tar.gz

./run-me-top-asap7-fakeram.sh

>>> llength [all_registers]
0
[WARNING GUI-0097] All pins are unconstrained. Cannot plot histogram. Check if timing data is loaded!
>>> report_clock_properties
Clock                   Period          Waveform
----------------------------------------------------

[hovind]

Nit: s/pruend/pruned

[jeffng-or]

The fact that there are no clocks make sense. The sram/fakeram/constraints-sram.sdc defines the clock variables, but the call to source $PLATFORM_DIR/constraints.sdc is being gated by the all_registers check. Since all_registers is returning an empty list, we never get to create the clocks.

In terms of all_registers, the liberty only has pin definitions, so not sure what we expect all_registers to report.

[oharboe]

If the .lib does not have any registers how can it store state? The symptom is no clock, the cause is that all_registers returns empty...