From 8043c90a04031c1619d0be7b1aba717e4f9968ac Mon Sep 17 00:00:00 2001
From: Clifford Wolf <clifford@clifford.at>
Date: Wed, 24 Aug 2016 15:20:23 +0200
Subject: [PATCH] Added REGS_INIT_ZERO parameter

---
 README.md  |  5 +++++
 picorv32.v | 11 +++++++++++
 2 files changed, 16 insertions(+)

diff --git a/README.md b/README.md
index 6c6e060..51eb17e 100644
--- a/README.md
+++ b/README.md
@@ -256,6 +256,11 @@ Set this to 0 to disable support for the `timer` instruction.
 
 Support for the timer is always disabled when ENABLE_IRQ is set to 0.
 
+#### REGS_INIT_ZERO (default = 0)
+
+Set this to 1 to initialize all registers to zero (using a Verilog `initial` block).
+This can be useful for simulation or formal verification.
+
 #### MASKED_IRQ (default = 32'h 0000_0000)
 
 A 1 bit in this bitmask corresponds to a permanently disabled IRQ.
diff --git a/picorv32.v b/picorv32.v
index e29f23c..2d2cf94 100644
--- a/picorv32.v
+++ b/picorv32.v
@@ -58,6 +58,7 @@ module picorv32 #(
 	parameter [ 0:0] ENABLE_IRQ = 0,
 	parameter [ 0:0] ENABLE_IRQ_QREGS = 1,
 	parameter [ 0:0] ENABLE_IRQ_TIMER = 1,
+	parameter [ 0:0] REGS_INIT_ZERO = 0,
 	parameter [31:0] MASKED_IRQ = 32'h 0000_0000,
 	parameter [31:0] LATCHED_IRQ = 32'h ffff_ffff,
 	parameter [31:0] PROGADDR_RESET = 32'h 0000_0000,
@@ -135,6 +136,14 @@ module picorv32 #(
 	reg [31:0] irq_pending;
 	reg [31:0] timer;
 
+	integer i;
+	initial begin
+		if (REGS_INIT_ZERO) begin
+			for (i = 0; i < regfile_size; i = i+1)
+				cpuregs[i] = 0;
+		end
+	end
+
 `ifdef DEBUGREGS
 	wire [31:0] dbg_reg_x0  = cpuregs[0];
 	wire [31:0] dbg_reg_x1  = cpuregs[1];
@@ -1882,6 +1891,7 @@ module picorv32_axi #(
 	parameter [ 0:0] ENABLE_IRQ = 0,
 	parameter [ 0:0] ENABLE_IRQ_QREGS = 1,
 	parameter [ 0:0] ENABLE_IRQ_TIMER = 1,
+	parameter [ 0:0] REGS_INIT_ZERO = 0,
 	parameter [31:0] MASKED_IRQ = 32'h 0000_0000,
 	parameter [31:0] LATCHED_IRQ = 32'h ffff_ffff,
 	parameter [31:0] PROGADDR_RESET = 32'h 0000_0000,
@@ -1983,6 +1993,7 @@ module picorv32_axi #(
 		.ENABLE_IRQ          (ENABLE_IRQ          ),
 		.ENABLE_IRQ_QREGS    (ENABLE_IRQ_QREGS    ),
 		.ENABLE_IRQ_TIMER    (ENABLE_IRQ_TIMER    ),
+		.REGS_INIT_ZERO      (REGS_INIT_ZERO      ),
 		.MASKED_IRQ          (MASKED_IRQ          ),
 		.LATCHED_IRQ         (LATCHED_IRQ         ),
 		.PROGADDR_RESET      (PROGADDR_RESET      ),