docs: add some tips on large designs, review followup

Signed-off-by: Øyvind Harboe <[email protected]>

Author: oharboe

docs/user/FlowVariables.md

@@ -242,7 +242,7 @@ configuration file.
 | <a name="SYNTH_HDL_FRONTEND"></a>SYNTH_HDL_FRONTEND| Select an alternative language frontend to ingest the design. Available option is "slang". If the variable is empty, design is read with the Yosys read_verilog command.| |
 | <a name="SYNTH_HIERARCHICAL"></a>SYNTH_HIERARCHICAL| Enable to Synthesis hierarchically, otherwise considered flat synthesis.| 0|
 | <a name="SYNTH_HIER_SEPARATOR"></a>SYNTH_HIER_SEPARATOR| Separator used for the synthesis flatten stage.| .|
-| <a name="SYNTH_KEEP_MOCKED_MEMORIES"></a>SYNTH_KEEP_MOCKED_MEMORIES| Keeping the mocked memories(not flattening them), preserves some of the access logic complexity and avoids optimizations outside of the mocked memory.| 1|
+| <a name="SYNTH_KEEP_MOCKED_MEMORIES"></a>SYNTH_KEEP_MOCKED_MEMORIES| When `SYNTH_MOCK_LARGE_MEMORIES=1`, setting this to 1, will keep mocked memories (not flattening them). This preserves some of the access logic complexity and avoids optimizations outside of the mocked memory.| 1|
 | <a name="SYNTH_KEEP_MODULES"></a>SYNTH_KEEP_MODULES| Mark modules to keep from getting removed in flattening.| |
 | <a name="SYNTH_MEMORY_MAX_BITS"></a>SYNTH_MEMORY_MAX_BITS| Maximum number of bits for memory synthesis. Ideally, real RAM or realistic fakeram should be used for RAMs much larger than 1024 bits. To temporarily ignore the RAM concerns and investigate other aspects of the design, consider setting `SYNTH_MOCK_LARGE_MEMORIES=1`, or adjusting `SYNTH_MEMORY_MAX_BITS`.| 4096|
 | <a name="SYNTH_MINIMUM_KEEP_SIZE"></a>SYNTH_MINIMUM_KEEP_SIZE| For hierarchical synthesis, we keep modules of larger area than given by this variable and flatten smaller modules. The area unit used is the size of a basic nand2 gate from the platform's standard cell library. The default value is platform specific.| 0|

flow/scripts/variables.yaml

@@ -230,9 +230,11 @@ SYNTH_MOCK_LARGE_MEMORIES:
     - synth
 SYNTH_KEEP_MOCKED_MEMORIES:
   description: >
-    Keeping the mocked memories(not flattening them), preserves some of
-    the access logic complexity and avoids optimizations outside
-    of the mocked memory.
+    When `SYNTH_MOCK_LARGE_MEMORIES=1`, setting this to 1,
+    will keep mocked memories (not flattening them).
+
+    This preserves some of the access logic complexity and
+    avoids optimizations outside of the mocked memory.
   default: 1
   stages:
     - synth