Doc support for overriding enum/string parameters at the top level

Signed-off-by: Pirmin Vogel <vogelpi@lowrisc.org>

doc/integration.rst

@@ -125,6 +125,16 @@ Parameters
 
 Any parameter marked *EXPERIMENTAL* when enabled is not verified to the same standard as the rest of the Ibex core.
 
+Note that Ibex uses SystemVerilog enum parameters e.g. for ``RV32M`` and ``RV32B``.
+This is well supported by most tools but some care is needed when overriding these parameters at the top level:
+
+* Synopsys VCS does not support overriding enum and string parameters at the top level via command line.
+  As a workaround, SystemVerilog defines are used in Ibex top level files simulated with VCS.
+  These defines can be set via command line.
+
+* Yosys does not support overriding enum parameters at the top level by setting enum names.
+  Instead, the enum values need to be used.
+
 Interfaces
 ----------
 

dv/uvm/core_ibex/tb/core_ibex_tb_top.sv

@@ -29,8 +29,10 @@ module core_ibex_tb_top;
   // CSR access interface
   core_ibex_csr_if csr_if(.clk(clk));
 
-  // You cannot override string parameters in VCS via the command line so a `define is used instead
-  // that can be set from the command line. If no value has been specified this gives a default.
+  // VCS does not support overriding enum and string parameters via command line. Instead, a
+  // `define is used that can be set from the command line. If no value has been specified, this
+  // gives a default. Other simulators don't take the detour via `define and can override the
+  // corresponding parameters directly.
   `ifndef IBEX_CFG_RV32M
     `define IBEX_CFG_RV32M ibex_pkg::RV32MFast
   `endif

examples/simple_system/rtl/ibex_simple_system.sv

@@ -2,6 +2,10 @@
 // Licensed under the Apache License, Version 2.0, see LICENSE for details.
 // SPDX-License-Identifier: Apache-2.0
 
+// VCS does not support overriding enum and string parameters via command line. Instead, a `define
+// is used that can be set from the command line. If no value has been specified, this gives a
+// default. Other simulators don't take the detour via `define and can override the corresponding
+// parameters directly.
 `ifndef RV32M
   `define RV32M ibex_pkg::RV32MFast
 `endif