From c10125eb5cb91968f724cea3092252159af207d7 Mon Sep 17 00:00:00 2001
From: Clifford Wolf <clifford@clifford.at>
Date: Thu, 2 Jul 2015 12:29:06 +0200
Subject: Added TWO_STAGE_SHIFT parameter

---
 README.md  | 7 +++++++
 picorv32.v | 5 ++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 808d351..03b0903 100644
--- a/README.md
+++ b/README.md
@@ -158,6 +158,13 @@ latches the value internally.
 This parameter is only available for the `picorv32` core. In the
 `picorv32_axi` core this is implicitly set to 0.
 
+#### TWO_STAGE_SHIFT (default = 1)
+
+By default shift operations are performed in two stages: first shift in units
+of 4 bits and then shift in units of 1 bit. This speeds up shift operations,
+but adds additional hardware. Set this parameter to 0 to disable the two-stage
+shift to further reduce the size of the core.
+
 #### CATCH_MISALIGN (default = 1)
 
 Set this to 0 to disable the circuitry for catching misaligned memory
diff --git a/picorv32.v b/picorv32.v
index fbb0b37..9aba3c4 100644
--- a/picorv32.v
+++ b/picorv32.v
@@ -36,6 +36,7 @@ module picorv32 #(
 	parameter [ 0:0] ENABLE_REGS_16_31 = 1,
 	parameter [ 0:0] ENABLE_REGS_DUALPORT = 1,
 	parameter [ 0:0] LATCHED_MEM_RDATA = 0,
+	parameter [ 0:0] TWO_STAGE_SHIFT = 1,
 	parameter [ 0:0] CATCH_MISALIGN = 1,
 	parameter [ 0:0] CATCH_ILLINSN = 1,
 	parameter [ 0:0] ENABLE_PCPI = 0,
@@ -885,7 +886,7 @@ module picorv32 #(
 					reg_out <= reg_op1;
 					mem_do_rinst <= mem_do_prefetch;
 					cpu_state <= cpu_state_fetch;
-				end else if (reg_sh >= 4) begin
+				end else if (TWO_STAGE_SHIFT && reg_sh >= 4) begin
 					(* parallel_case, full_case *)
 					case (1'b1)
 						instr_slli || instr_sll: reg_op1 <= reg_op1 << 4;
@@ -1136,6 +1137,7 @@ module picorv32_axi #(
 	parameter [ 0:0] ENABLE_COUNTERS = 1,
 	parameter [ 0:0] ENABLE_REGS_16_31 = 1,
 	parameter [ 0:0] ENABLE_REGS_DUALPORT = 1,
+	parameter [ 0:0] TWO_STAGE_SHIFT = 1,
 	parameter [ 0:0] CATCH_MISALIGN = 1,
 	parameter [ 0:0] CATCH_ILLINSN = 1,
 	parameter [ 0:0] ENABLE_PCPI = 0,
@@ -1230,6 +1232,7 @@ module picorv32_axi #(
 		.ENABLE_COUNTERS     (ENABLE_COUNTERS     ),
 		.ENABLE_REGS_16_31   (ENABLE_REGS_16_31   ),
 		.ENABLE_REGS_DUALPORT(ENABLE_REGS_DUALPORT),
+		.TWO_STAGE_SHIFT     (TWO_STAGE_SHIFT     ),
 		.CATCH_MISALIGN      (CATCH_MISALIGN      ),
 		.CATCH_ILLINSN       (CATCH_ILLINSN       ),
 		.ENABLE_PCPI         (ENABLE_PCPI         ),
-- 
cgit