pfv: add configurable memory alignment constraints.

Before this commit, the `mem_aligned` parameter assumed a 64-bit data
bus when set to True.

cores/microwatt/microwatt_cli/core.py

@@ -138,7 +138,7 @@ class MicrowattWrapper(Elaboratable):
     """)
 
     def __init__(self, *, bus_fairness=False, **kwargs):
-        self.pfv     = pfv.Interface(mem_aligned=False, illegal_insn_heai=False, muldiv_altops=True)
+        self.pfv     = pfv.Interface(mem_alignment=0, illegal_insn_heai=False, muldiv_altops=True)
         self.wb_insn = wishbone.Interface(addr_width=29, data_width=64, granularity=8,
                                           features=("stall",))
         self.wb_data = wishbone.Interface(addr_width=29, data_width=64, granularity=8,

power_fv/check/insn/__init__.py

@@ -31,7 +31,7 @@ class InsnCheck(PowerFVCheck, metaclass=InsnCheckMeta):
         self.spec = self.spec_cls(
             insn              = self.insn,
             gpr_width         = self.dut.pfv.gpr_width,
-            mem_aligned       = self.dut.pfv.mem_aligned,
+            mem_alignment     = self.dut.pfv.mem_alignment,
             illegal_insn_heai = self.dut.pfv.illegal_insn_heai,
             muldiv_altops     = self.dut.pfv.muldiv_altops,
         )

power_fv/insn/spec/loadstore.py

@@ -118,33 +118,27 @@ class LoadStoreSpec(InsnSpec, Elaboratable):
 
             m.d.comb += ea.eq(iea(ea_base + ea_offset, self.pfv.msr.r_data.sf))
 
-            byte_offset = Signal(3)
-            half_offset = Signal(2)
-            word_offset = Signal(1)
-
-            # If `pfv.mem_aligned` is set, `pfv.mem.addr` points to the dword containing EA.
-            # If `pfv.mem_aligned` is unset, `pfv.mem.addr` is equal to EA.
+            # The value of `pfv.mem.addr` must be equal to EA, rounded down to a multiple of
+            # ``2 ** pfv.mem_alignment``.
 
-            m.d.comb += self.pfv.mem.addr[3:].eq(ea[3:])
-
-            if self.pfv.mem_aligned:
-                m.d.comb += [
-                    self.pfv.mem.addr[:3].eq(0),
-                    byte_offset.eq(ea[:3]),
-                ]
-            else:
             m.d.comb += [
-                    self.pfv.mem.addr[:3].eq(ea[:3]),
-                    byte_offset.eq(0),
+                self.pfv.mem.addr[self.pfv.mem_alignment:].eq(ea[self.pfv.mem_alignment:]),
+                self.pfv.mem.addr[:self.pfv.mem_alignment].eq(0),
             ]
 
+            # Raise an Alignment Interrupt if EA is misaligned to the size of the storage operand
+            # and to ``2 ** pfv.mem_alignment``.
+
+            byte_offset = Signal(3)
+            half_offset = Signal(2)
+            word_offset = Signal(1)
+
             m.d.comb += [
+                byte_offset.eq(ea[:self.pfv.mem_alignment]),
                 half_offset.eq(byte_offset[1:]),
                 word_offset.eq(byte_offset[2:]),
             ]
 
-            # Raise an Alignment Interrupt if EA is misaligned wrt. `pfv.mem`
-
             ea_misaligned = Signal()
 
             if isinstance(self.insn, (

power_fv/pfv.py

@@ -109,11 +109,12 @@ class Interface(Record):
     gpr_width : int
         General-purpose register width. Either 32 or 64. Compliance with Power ISA versions above
         v2.7B requires 64-bit wide GPRs.
-    mem_aligned : bool
-        If ``True``, an Alignment interrupt is expected if the effective address of a Load/Store
-        operation is not aligned to its operand; ``mem.addr`` is also expected to be aligned to
-        8 bytes. If ``False``, ``mem.addr`` is expected to point to the least- or most-significant
-        byte of the storage operand, depending on the current endian mode.
+    mem_alignment : log2 of int
+        Memory alignment. This parameter restricts the alignment of Load/Store accesses to either
+        ``2 ** pfv.mem_alignment`` bytes, or to the size of their operand. Otherwise, an Alignment
+        interrupt is triggered. A core that can transparently handle misaligned accesses may set
+        this value to 0, whereas one that requires software intervention may set it to the width
+        of its data bus (as a log2).
     illegal_insn_heai : bool
         If ``True``, an illegal instruction triggers an Hypervisor Emulation Assistance interrupt.
         Otherwise, it triggers an Illegal Instruction type Program interrupt (which was removed in
@@ -218,13 +219,16 @@ class Interface(Record):
     srr1 : Record(:func:`reg_port_layout`)
         Save/Restore Register 1 access.
     """
-    def __init__(self, *, gpr_width=64, mem_aligned=False, illegal_insn_heai=False,
+    def __init__(self, *, gpr_width=64, mem_alignment=0, illegal_insn_heai=False,
                  muldiv_altops=False, name=None, src_loc_at=0):
         if gpr_width not in (32, 64):
             raise ValueError("GPR width must be 32 or 64, not {!r}".format(gpr_width))
+        if mem_alignment not in (0, 1, 2, 3):
+            raise ValueError("Memory alignment must be an integer between 0 and 3, not {!r}"
+                             .format(mem_alignment))
 
         self.gpr_width         = gpr_width
-        self.mem_aligned       = bool(mem_aligned)
+        self.mem_alignment     = mem_alignment
         self.illegal_insn_heai = bool(illegal_insn_heai)
         self.muldiv_altops     = bool(muldiv_altops)