From 565b76672a03e6d408463d7ede13d3f584bf5b4c Mon Sep 17 00:00:00 2001
From: Luke Wren <wren6991@gmail.com>
Date: Sun, 30 May 2021 18:42:43 +0100
Subject: [PATCH] Make MVENDORID/MARCHID/MIMPID configurable

---
 hdl/hazard3_config.vh | 14 ++++++++++++++
 hdl/hazard3_csr.v     | 15 ++++++++-------
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/hdl/hazard3_config.vh b/hdl/hazard3_config.vh
index 7518e60..fdb24eb 100644
--- a/hdl/hazard3_config.vh
+++ b/hdl/hazard3_config.vh
@@ -35,6 +35,20 @@ parameter CSR_M_TRAP      = 1,
 // CSR_COUNTER: Include performance counters and relevant M-mode CSRs
 parameter CSR_COUNTER     = 0,
 
+// ----------------------------------------------------------------------------
+// ID registers
+
+// JEDEC JEP106-compliant vendor ID, can be left at 0 if "not implemented or
+// that this is a non-commercial implementation" (RISC-V spec).
+// 31:7 is continuation code count, 6:0 is ID. Parity bit is not stored.
+parameter MVENDORID_VAL = 32'h0,
+
+// Architecture ID for Hazard3, currently 0 because unregistered. (TODO)
+parameter MARCHID_VAL = 32'h0,
+
+// Implementation ID for this specific version of Hazard3. Git hash is perfect.
+parameter MIMPID_VAL = 32'h0,
+
 // ----------------------------------------------------------------------------
 // Performance/size options
 
diff --git a/hdl/hazard3_csr.v b/hdl/hazard3_csr.v
index 4d164e2..222724e 100644
--- a/hdl/hazard3_csr.v
+++ b/hdl/hazard3_csr.v
@@ -419,7 +419,7 @@ always @ (*) begin
 		decode_match = 1'b1;
 		rdata = {
 			2'h1,              // MXL: 32-bit
-			{XLEN-28{1'b0}}, // WLRL
+			{XLEN-28{1'b0}},   // WLRL
 
 			13'd0,             // Z...N, no
 			|EXTENSION_M,
@@ -432,18 +432,15 @@ always @ (*) begin
 	end
 	MVENDORID: if (CSR_M_MANDATORY) begin
 		decode_match = !wen_soon; // MRO
-		// I don't have a JEDEC ID. It is legal to tie this to 0 if non-commercial.
-		rdata = {XLEN{1'b0}};
+		rdata = MVENDORID_VAL;
 	end
 	MARCHID: if (CSR_M_MANDATORY) begin
 		decode_match = !wen_soon; // MRO
-		// I don't have a RV foundation ID. It is legal to tie this to 0.
-		rdata = {XLEN{1'b0}};
+		rdata = MARCHID_VAL;
 	end
 	MIMPID: if (CSR_M_MANDATORY) begin
 		decode_match = !wen_soon; // MRO
-		// TODO put git SHA or something here
-		rdata = {XLEN{1'b0}};
+		rdata = MIMPID_VAL;
 	end
 	MHARTID: if (CSR_M_MANDATORY) begin
 		decode_match = !wen_soon; // MRO
@@ -473,6 +470,10 @@ always @ (*) begin
 		};
 	end
 
+	// MSTATUSH is not implemented (permitted when all fields would be tied to
+	// zero -- those fields being MBE and SBE, which are zero because we are
+	// pure little-endian.)
+
 	// MEDELEG, MIDELEG should not exist for M-only implementations. Will raise
 	// illegal instruction exception if accessed.