makefile: check that inferred memories are smaller than SYNTH_MEMORY_MAX_BITS

Dusted off some code that Tutu wrote to create a report of
memories in the design.

Before even trying synthesis optimization, it is useful to know
what memories are in the design, error out by default when there
are too big memories in the design. Adjust this threshold by
changing SYNTH_MEMORY_MAX_BITS, default 4096 bits.

If the memories are small(Tutu mentioned that 1024 bits or smaller, same
as Chipyard uses), then they are best instantiated as flip flops.

Running `make memory` prints out the report after synthesis.

Signed-off-by: Øyvind Harboe <[email protected]>
Co-author: Tutu Ajayi <[email protected]>

Author: oharboe

flow/Makefile

@@ -458,12 +458,18 @@ synth-report: synth
 do-synth-report:
 	($(TIME_CMD) $(OPENROAD_CMD) $(SCRIPTS_DIR)/synth_metrics.tcl) 2>&1 | tee -a $(LOG_DIR)/1_1_yosys.log
 
+.PHONY: memory
+memory: $(RESULTS_DIR)/mem.json
+	python3 $(SCRIPTS_DIR)/mem_dump.py $(RESULTS_DIR)/mem.json
+
 # ==============================================================================
 
 
 # Run Synthesis using yosys
 #-------------------------------------------------------------------------------
-SYNTH_SCRIPT ?= $(SCRIPTS_DIR)/synth.tcl
+
+export SYNTH_SCRIPT ?= $(SCRIPTS_DIR)/synth.tcl
+export SYNTH_MEMORY_MAX_BITS ?= 4096
 
 $(SYNTH_STOP_MODULE_SCRIPT):
 	mkdir -p $(RESULTS_DIR) $(LOG_DIR) $(REPORTS_DIR)
@@ -484,7 +490,7 @@ yosys-dependencies: $(DONT_USE_LIBS) $(WRAPPED_LIBS) $(DONT_USE_SC_LIB) $(DFF_LI
 
 .PHONY: do-yosys
 do-yosys: yosys-dependencies
-	mkdir -p $(RESULTS_DIR) $(LOG_DIR) $(REPORTS_DIR)
+	mkdir -p $(RESULTS_DIR) $(LOG_DIR) $(REPORTS_DIR) $(OBJECTS_DIR)
 	($(TIME_CMD) $(YOSYS_CMD) $(YOSYS_FLAGS) -c $(SYNTH_SCRIPT)) 2>&1 | tee $(LOG_DIR)/1_1_yosys.log
 
 $(RESULTS_DIR)/1_1_yosys.v: $(SDC_FILE_CLOCK_PERIOD)
@@ -504,7 +510,7 @@ $(RESULTS_DIR)/1_synth.v: $(RESULTS_DIR)/1_1_yosys.v
 
 .PHONY: clean_synth
 clean_synth:
-	rm -f $(RESULTS_DIR)/1_*.v $(RESULTS_DIR)/1_synth.sdc
+	rm -f $(RESULTS_DIR)/1_*.v $(RESULTS_DIR)/1_synth.sdc $(RESULTS_DIR)/mem.json
 	rm -f $(REPORTS_DIR)/synth_*
 	rm -f $(LOG_DIR)/1_*
 	rm -f $(SYNTH_STOP_MODULE_SCRIPT)

flow/designs/sky130hd/microwatt/config.mk

@@ -41,3 +41,7 @@ export SKIP_GATE_CLONING = 1
 export export SETUP_SLACK_MARGIN = 0.2
 
 export GLOBAL_ROUTE_ARGS=-congestion_iterations 100 -verbose
+
+# This is high, some SRAMs should probably be converted
+# to real SRAMs and not instantiated as flops
+export SYNTH_MEMORY_MAX_BITS ?= 42000

flow/scripts/mem_dump.py

@@ -0,0 +1,45 @@
+import argparse
+import json
+import os
+import sys
+
+
+def format_ram_table_from_json(data, max_bits=None):
+    formatting = "{:<15} | {:<15} | {:<15} | {:<50}\n"
+    table = formatting.format("Rows",
+                              "Width",
+                              "Total bits",
+                              "Name")
+    table += "-"*len(table) + "\n"
+    max_ok = True
+    for module_name, module_info in data["modules"].items():
+        cells = module_info["cells"]
+        for memory, cell in cells.items():
+            if not cell["type"].startswith("$mem"):
+                continue
+            parameters = cell["parameters"]
+            size = int(parameters["SIZE"], 2)
+            width = int(parameters["WIDTH"], 2)
+            bits = size * width
+            table += formatting.format(size,
+                                       width,
+                                       bits,
+                                       module_name + "." + memory)
+            if max_bits is not None and bits > max_bits:
+                max_ok = False
+    return table, max_ok
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument("file")
+    parser.add_argument("-m", "--max-bits", type=int, default=None)
+    args = parser.parse_args()
+
+    with open(args.file, 'r') as file:
+        json_data = json.load(file)
+    formatted_table, max_ok = format_ram_table_from_json(json_data, args.max_bits)
+    print()
+    print(formatted_table)
+    if not max_ok:
+        sys.exit("ERROR: Synthesized memory size exceeds maximum allowed bits " + str(args.max_bits))

flow/scripts/synth.tcl

@@ -12,10 +12,7 @@ if { [info exist ::env(SYNTH_GUT)] && $::env(SYNTH_GUT) == 1 } {
   delete $::env(DESIGN_NAME)/c:*
 }
 
-# Generic synthesis
-synth -top $::env(DESIGN_NAME) {*}$::env(SYNTH_ARGS)
-# Get rid of indigestibles
-chformal -remove
+synthesize_check $::env(SYNTH_ARGS)
 
 if { [info exists ::env(USE_LSORACLE)] } {
     set lso_script [open $::env(OBJECTS_DIR)/lso.script w]

flow/scripts/synth_hier_report.tcl

@@ -1,7 +1,7 @@
 source $::env(SCRIPTS_DIR)/synth_preamble.tcl
 
-# Hierarchical synthesis
-synth  -top $::env(DESIGN_NAME)
+synthesize_check {}
+
 if { [info exist ::env(ADDER_MAP_FILE)] && [file isfile $::env(ADDER_MAP_FILE)] } {
   techmap -map $::env(ADDER_MAP_FILE)
 }

flow/scripts/synth_preamble.tcl

@@ -105,3 +105,14 @@ set constr [open $::env(OBJECTS_DIR)/abc.constr w]
 puts $constr "set_driving_cell $::env(ABC_DRIVER_CELL)"
 puts $constr "set_load $::env(ABC_LOAD_IN_FF)"
 close $constr
+
+proc synthesize_check {synth_args} {
+  # Generic synthesis
+  synth -top $::env(DESIGN_NAME) -run :fine {*}$synth_args
+  json -o $::env(RESULTS_DIR)/mem.json
+  # Run report and check here so as to fail early if this synthesis run is doomed
+  exec -- python3 $::env(SCRIPTS_DIR)/mem_dump.py --max-bits $::env(SYNTH_MEMORY_MAX_BITS) $::env(RESULTS_DIR)/mem.json
+  synth -top $::env(DESIGN_NAME) -run fine: {*}$synth_args
+  # Get rid of indigestibles
+  chformal -remove
+}