Fix address bit ordering in sky130 1rw characterization

compiler/characterizer/delay.py

@@ -1388,11 +1388,15 @@ class delay(simulation):
     def calculate_inverse_address(self):
         """Determine dummy test address based on probe address and column mux size."""
 
-        # The inverse address needs to share the same bitlines as the probe address as the trimming will remove all other bitlines
+        # The inverse address needs to share the same bitlines as the probe address as the trimming will remove all other bitlines.
         # This is only an issue when there is a column mux and the address maps to different bitlines.
         column_addr = self.get_column_addr() # do not invert this part
         inverse_address = ""
-        for c in self.probe_address[self.sram.col_addr_size:]: # invert everything else
+        if self.sram.col_addr_size > 0:
+            row_address = self.probe_address[:-self.sram.col_addr_size]
+        else:
+            row_address = self.probe_address
+        for c in row_address: # invert row bits only
             if c=="0":
                 inverse_address += "1"
             elif c=="1":

compiler/characterizer/simulation.py

@@ -126,8 +126,10 @@ class simulation():
     def get_data_bit_column_number(self, probe_address, probe_data):
         """Calculates bitline column number of data bit under test using bit position and mux size"""
 
-        if self.sram.col_addr_size>0:
-            col_address = int(probe_address[0:self.sram.col_addr_size], 2)
+        # Address pins are ordered a*_0 ... a*_N, where a*_0 is the LSB.
+        # So the column mux select bits are the rightmost bits in the binary address string.
+        if self.sram.col_addr_size > 0:
+            col_address = int(probe_address[-self.sram.col_addr_size:], 2)
         else:
             col_address = 0
         bl_column = int(self.sram.words_per_row * probe_data + col_address)
@@ -136,7 +138,11 @@ class simulation():
     def get_address_row_number(self, probe_address):
         """Calculates wordline row number of data bit under test using address and column mux size"""
 
-        return int(probe_address[self.sram.col_addr_size:], 2)
+        if self.sram.col_addr_size > 0:
+            row_address = probe_address[:-self.sram.col_addr_size]
+        else:
+            row_address = probe_address
+        return int(row_address, 2) if row_address else 0
 
     def add_control_one_port(self, port, op):
         """Appends control signals for operation to a given port"""
@@ -484,7 +490,9 @@ class simulation():
 
     def get_column_addr(self):
         """Returns column address of probe bit"""
-        return self.probe_address[:self.sram.col_addr_size]
+        if self.sram.col_addr_size == 0:
+            return ""
+        return self.probe_address[-self.sram.col_addr_size:]
 
     def add_graph_exclusions(self):
         """

compiler/characterizer/trim_spice.py

@@ -56,12 +56,15 @@ class trim_spice():
         # Always start fresh if we do multiple reductions
         self.sp_buffer = self.spice
 
-        # Split up the address and convert to an int
-        wl_address = int(address[self.col_addr_size:], 2)
+        # Address pins are ordered with bit 0 as LSB, so mux column bits
+        # are the rightmost bits in the binary address string.
         if self.col_addr_size > 0:
-            col_address = int(address[0:self.col_addr_size], 2)
+            row_address = address[:-self.col_addr_size]
+            col_address = int(address[-self.col_addr_size:], 2)
         else:
+            row_address = address
             col_address = 0
+        wl_address = int(row_address, 2) if row_address else 0
 
         # 1. Keep cells in the bitcell array based on WL and BL
         wl_name = "wl_{}".format(wl_address)