Implement ALU shifter

1 files changed, 85 insertions, 31 deletions

diff --git a/rtl/core/cycles.sv b/rtl/core/cycles.sv
index 84bbd32..f503188 100644
--- a/rtl/core/cycles.sv
+++ b/rtl/core/cycles.sv
@@ -2,63 +2,116 @@
 
 module core_cycles
 (
-	input  logic      clk,
-	                  dec_execute,
-	                  dec_branch,
-	                  dec_writeback,
-	                  dec_update_flags,
-	input  ptr        dec_branch_offset,
-	input  alu_decode dec_alu,
-	input  ptr        fetch_insn_pc,
+	input  logic       clk,
+	                   dec_execute,
+	                   dec_branch,
+	                   dec_writeback,
+	                   dec_update_flags,
+	input  ptr         dec_branch_offset,
+	input  alu_decode  dec_alu,
+	input  ptr         fetch_insn_pc,
+	input  word        rd_value_b,
 
 	output logic       stall,
 	                   branch,
 	                   writeback,
 	                   update_flags,
 	output reg_num     rd,
+	                   ra,
+	                   rb,
 	output ptr         branch_target,
 	                   pc,
 	                   pc_visible,
 	output psr_mode    reg_mode,
-	output alu_control alu
+	output alu_control alu,
+	output word        alu_base,
+	output logic[7:0]  alu_shift
 );
 
 	enum
 	{
-		EXECUTE
+		EXECUTE,
+		RD_SHIFT
 	} cycle, next_cycle;
 
+	logic final_writeback, data_snd_is_imm, data_snd_shift_by_reg;
+	logic[5:0] data_shift_imm;
+	logic[7:0] data_imm;
+	word saved_base;
+	reg_num r_shift;
+
 	assign stall = next_cycle != EXECUTE;
 	assign pc_visible = pc + 2;
-	assign next_cycle = EXECUTE; //TODO
 	assign reg_mode = `MODE_SVC; //TODO
 
+	always_comb begin
+		next_cycle = EXECUTE;
+		if((cycle == EXECUTE) & data_snd_shift_by_reg)
+			next_cycle = RD_SHIFT;
+
+		unique case(cycle)
+			RD_SHIFT:
+				alu_base = saved_base;
+
+			default:
+				if(data_snd_is_imm)
+					alu_base = {{24{1'b0}}, data_imm};
+				else
+					alu_base = rd_value_b;
+		endcase
+
+		unique case(cycle)
+			RD_SHIFT: alu_shift = rd_value_b[7:0];
+			default:  alu_shift = {2'b00, data_shift_imm};
+		endcase
+	end
+
 	always_ff @(posedge clk) begin
 		cycle <= next_cycle;
 
-		if(next_cycle == EXECUTE) begin
-			branch <= 0;
-			writeback <= 0;
-			update_flags <= 0;
-			branch_target <= 30'bxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx;
+		unique case(next_cycle)
+			EXECUTE: begin
+				branch <= 0;
+				writeback <= 0;
+				update_flags <= 0;
+				branch_target <= 30'bxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx;
 
-			if(dec_execute) begin
-				branch <= dec_branch;
-				writeback <= dec_writeback;
-				branch_target <= pc_visible + dec_branch_offset;
+				if(dec_execute) begin
+					branch <= dec_branch;
+					writeback <= dec_writeback & ~dec_alu.snd_shift_by_reg;
+					update_flags <= dec_update_flags;
+					branch_target <= pc_visible + dec_branch_offset;
+
+					data_snd_is_imm <= dec_alu.snd_is_imm;
+					data_snd_shift_by_reg <= dec_alu.snd_shift_by_reg;
+					data_imm <= dec_alu.imm;
+					data_shift_imm <= dec_alu.shift_imm;
+
+					alu.op <= dec_alu.op;
+					alu.shl <= dec_alu.shl;
+					alu.shr <= dec_alu.shr;
+					alu.ror <= dec_alu.ror;
+					alu.put_carry <= dec_alu.put_carry;
+					alu.sign_extend <= dec_alu.sign_extend;
+
+					rd <= dec_alu.rd;
+					ra <= dec_alu.rn;
+					rb <= dec_alu.r_snd;
+					r_shift <= dec_alu.r_shift;
+
+					final_writeback <= dec_writeback;
+				end
+
+				pc <= fetch_insn_pc;
 			end
 
-			alu.op <= dec_alu.op;
-			alu.shl <= dec_alu.shl;
-			alu.shr <= dec_alu.shr;
-			alu.ror <= dec_alu.ror;
-			alu.put_carry <= dec_alu.put_carry;
-			alu.sign_extend <= dec_alu.sign_extend;
-
-			pc <= fetch_insn_pc;
-			rd <= dec_alu.rd;
-			update_flags <= dec_update_flags;
-		end
+			RD_SHIFT: begin
+				rb <= r_shift;
+				data_snd_shift_by_reg <= 0;
+				saved_base <= rd_value_b;
+				writeback <= final_writeback;
+			end
+		endcase
 	end
 
 	initial begin
@@ -66,6 +119,7 @@ module core_cycles
 
 		branch = 1;
 		writeback = 0;
+		data_snd_shift_by_reg = 0;
 		branch_target = 30'd0;
 		pc = 0;
 	end