E extension (#440)

coreblocks/frontend/decoder.py

@@ -357,6 +357,11 @@ def elaborate(self, platform):
         m = Module()
 
         extensions = self.gen.isa.extensions
+
+        # We need to support all I instructions in E extension, but this is not extension implication
+        if Extension.E in extensions:
+            extensions |= Extension.I
+
         supported_encodings: set[Encoding] = set()
         encoding_to_optype: dict[Encoding, OpType] = dict()
         for ext, optypes in optypes_by_extensions.items():
@@ -397,10 +402,20 @@ def elaborate(self, platform):
             self._extract(20, self.funct12),
         ]
 
+        rd_field = Signal(self.gen.isa.reg_field_bits)
+        rs1_field = Signal(self.gen.isa.reg_field_bits)
+        rs2_field = Signal(self.gen.isa.reg_field_bits)
+
+        m.d.comb += [
+            self._extract(7, rd_field),
+            self._extract(15, rs1_field),
+            self._extract(20, rs2_field),
+        ]
+
         m.d.comb += [
-            self._extract(7, self.rd),
-            self._extract(15, self.rs1),
-            self._extract(20, self.rs2),
+            self.rd.eq(rd_field),
+            self.rs1.eq(rs1_field),
+            self.rs2.eq(rs2_field),
         ]
 
         rd_invalid = Signal()
@@ -480,6 +495,15 @@ def elaborate(self, platform):
             self._extract(28, self.fm),
         ]
 
+        # Check if register field bits outside of logical register space are zeroed
+
+        register_space_invalid = Signal()
+        m.d.comb += register_space_invalid.eq(
+            (self.rd_v & (rd_field[len(self.rd) :]).any())
+            | (self.rs1_v & (rs1_field[len(self.rs1) :]).any())
+            | (self.rs2_v & (rs2_field[len(self.rs2) :]).any())
+        )
+
         # CSR address
 
         m.d.comb += self._extract(20, self.csr)
@@ -510,6 +534,6 @@ def elaborate(self, platform):
         # 0b11 at field [0:2] of instruction specify standard 32-bit instruction encoding space (not checked by opcode)
         encoding_space = Signal(2)
         m.d.comb += self._extract(0, encoding_space)
-        m.d.comb += self.illegal.eq((self.optype == OpType.UNKNOWN) | (encoding_space != 0b11))
+        m.d.comb += self.illegal.eq((self.optype == OpType.UNKNOWN) | (encoding_space != 0b11) | register_space_invalid)
 
         return m

coreblocks/params/configurations.py

@@ -89,11 +89,13 @@ def replace(self, **kwargs):
 
 # Minimal core configuration
 tiny_core_config = CoreConfiguration(
+    embedded=True,
     func_units_config=(
         RSBlockComponent([ALUComponent(), ShiftUnitComponent(), JumpComponent()], rs_entries=2),
         LSUBlockComponent(),
     ),
-    rob_entries_bits=6,
+    phys_regs_bits=basic_core_config.phys_regs_bits - 1,
+    rob_entries_bits=basic_core_config.rob_entries_bits - 1,
     allow_partial_extensions=True,  # No exception unit
 )
 

coreblocks/params/genparams.py

@@ -65,9 +65,6 @@ def __init__(self, cfg: CoreConfiguration):
         if not cfg.allow_partial_extensions and ext_partial != ext_full:
             raise RuntimeError(f"Extensions {ext_partial&~ext_full!r} are only partially supported")
 
-        if cfg.embedded:
-            raise RuntimeError("E extension is not supported yet")  # TODO: Remove after implementing E in decode
-
         extensions |= cfg._implied_extensions
         self.isa_str = gen_isa_string(extensions, cfg.xlen)
 

coreblocks/params/isa.py

@@ -237,11 +237,6 @@ class Extension(enum.IntFlag):
     G = I | M | A | F | D | ZICSR | ZIFENCEI
 
 
-# Extensions which are mutually exclusive
-_extension_exclusive = [
-    [Extension.I, Extension.E],
-]
-
 # Extensions which explicitly require another extension in order to be valid (can be joined using | operator)
 _extension_requirements = {
     Extension.D: Extension.F,
@@ -344,14 +339,6 @@ def parse_extension(e):
             if ext in self.extensions:
                 self.extensions |= imply
 
-        for exclusive in _extension_exclusive:
-            for i in range(len(exclusive)):
-                for j in range(i + 1, len(exclusive)):
-                    if exclusive[i] | exclusive[j] in self.extensions:
-                        raise RuntimeError(
-                            f"ISA extensions {exclusive[i].name} and {exclusive[j].name} are mutually exclusive"
-                        )
-
         for ext, requirements in _extension_requirements.items():
             if ext in self.extensions and requirements not in self.extensions:
                 for req in Extension:
@@ -360,7 +347,8 @@ def parse_extension(e):
                             f"ISA extension {ext.name} requires the {req.name} extension to be supported"
                         )
 
-        if self.extensions & Extension.E:
+        # I & E extensions can coexist if I extenstion can be disableable at runtime
+        if self.extensions & Extension.E and not self.extensions & Extension.I:
             self.reg_cnt = 16
         else:
             self.reg_cnt = 32
@@ -370,6 +358,8 @@ def parse_extension(e):
         self.ilen_bytes = self.ilen // 8
         self.ilen_log = self.ilen.bit_length() - 1
 
+        self.reg_field_bits = 5
+
         self.csr_alen = 12
 
 

test/frontend/test_decoder.py

@@ -267,6 +267,31 @@ def test_zbb(self):
             self.do_test(test)
 
 
+class TestDecoderEExtLegal(TestCaseWithSimulator):
+    E_TEST = [
+        (0x00000033, False),  # add x0, x0, x0
+        (0x00F787B3, False),  # add x15, x15, x15
+        (0x00F807B3, True),  # add x15, x16, x15
+        (0xFFF78793, False),  # addi x15, x15, -1
+        (0xFFF78813, True),  # addi x16, x15, -1
+        (0xFFFFF06F, False),  # jal x0, -2
+        (0xFFFFFF6F, True),  # jal x30, -2
+    ]
+
+    def test_e(self):
+        gen = GenParams(test_core_config.replace(embedded=True, _implied_extensions=Extension.E))
+        self.decoder = InstrDecoder(gen)
+
+        def process():
+            for encoding, illegal in self.E_TEST:
+                yield self.decoder.instr.eq(encoding)
+                yield Settle()
+                self.assertEqual((yield self.decoder.illegal), illegal)
+
+        with self.run_simulation(self.decoder) as sim:
+            sim.add_process(process)
+
+
 class TestEncodingUniqueness(TestCase):
     def test_encoding_uniqueness(self):
         code_type = tuple[Optional[int], Optional[int], Optional[int], Optional[int]]

test/params/test_configurations.py

@@ -18,7 +18,7 @@ class ISAStrTest:
     TEST_CASES = [
         ISAStrTest(basic_core_config, "rv32i", "rv32i", "rv32i"),
         ISAStrTest(full_core_config, "rv32imcbzicsr", "rv32imcbzicsr", "rv32imcbzicsr"),
-        ISAStrTest(tiny_core_config, "rv32i", "rv32", "rv32i"),
+        ISAStrTest(tiny_core_config, "rv32e", "rv32", "rv32e"),
         ISAStrTest(test_core_config, "rv32", "rv32", "rv32i"),
     ]
 

test/params/test_isa.py

@@ -119,8 +119,8 @@ def __init__(self, isa_str, valid, xlen=None, reg_cnt=None, extensions=None):
             | Extension.ZIFENCEI
             | Extension.ZICSR,
         ),
+        ISATestEntry("rv32ie", True, 32, 32, Extension.I | Extension.E),
         ISATestEntry("rv32", False),
-        ISATestEntry("rv32ie", False),
         ISATestEntry("rv64e", False),
         ISATestEntry("rv32fdc", False),
         ISATestEntry("rv32izicsrzmmul", False),