Fix for issue #782 (#783)

Author: stnolting

CHANGELOG.md

@@ -30,6 +30,7 @@ mimpid = 0x01040312 -> Version 01.04.03.12 -> v1.4.3.12
 
 | Date | Version | Comment | Link |
 |:----:|:-------:|:--------|:----:|
+| 31.01.2024 | 1.9.3.10 | close illegal compressed instruction decoding loophole | [#783](https://github.com/stnolting/neorv32/pull/783) |
 | 29.01.2024 | 1.9.3.9 | :test_tube: extend switchable clock domain (CPU bus switch, i-cache, d-cache) | [#780](https://github.com/stnolting/neorv32/pull/780) |
 | 29.01.2024 | 1.9.3.8 | top entity input ports now have default values `'L'` or `'h'` modeling a pull-down or pull-resistor in case they are not explicitly assigned during instantiation | [#779](https://github.com/stnolting/neorv32/pull/779) |
 | 28.01.2024 | 1.9.3.7 | FIFO module _NULL assertion_ fix | [#778](https://github.com/stnolting/neorv32/pull/778) |

rtl/core/neorv32_cpu_decompressor.vhd

@@ -317,6 +317,9 @@ begin
                     decoded(instr_funct3_msb_c downto instr_funct3_lsb_c) <= funct3_and_c;
                     decoded(instr_funct7_msb_c downto instr_funct7_lsb_c) <= "0000000";
                 end case;
+                if (ci_instr16_i(12) = '1') then -- reserved instruction space.
+                  illegal <= '1';
+                end if;
             end case;
 
         end case;

rtl/core/neorv32_package.vhd

@@ -56,7 +56,7 @@ package neorv32_package is
 
   -- Architecture Constants -----------------------------------------------------------------
   -- -------------------------------------------------------------------------------------------
-  constant hw_version_c : std_ulogic_vector(31 downto 0) := x"01090309"; -- hardware version
+  constant hw_version_c : std_ulogic_vector(31 downto 0) := x"01090310"; -- hardware version
   constant archid_c     : natural := 19; -- official RISC-V architecture ID
   constant XLEN         : natural := 32; -- native data path width