Split decoding of flexible second operand out of data instructions

3 files changed, 114 insertions, 66 deletions

diff --git a/rtl/core/decode/data.sv b/rtl/core/decode/data.sv
index a649440..e2a44df 100644
--- a/rtl/core/decode/data.sv
+++ b/rtl/core/decode/data.sv
@@ -6,45 +6,25 @@ module core_decode_data
 	input  word        insn,
 
 	output data_decode decode,
-	output logic       writeback,
+	output logic       snd_is_imm,
+	                   snd_shift_by_reg_if_reg,
+	                   writeback,
 	                   update_flags,
-	                   restore_spsr,
-	                   undefined
+	                   restore_spsr
 );
 
 	alu_op op;
-	reg_num rn, rd, r_snd, r_shift;
-	logic snd_shift_by_reg, snd_is_imm, shl, shr, ror, put_carry, sign_extend;
-	logic[7:0] imm;
-	logic[5:0] shift_imm;
+	reg_num rn, rd;
 
 	assign decode.op = op;
 	assign decode.rn = rn;
 	assign decode.rd = rd;
-	assign decode.r_snd = r_snd;
-	assign decode.r_shift = r_shift;
-	assign decode.snd_shift_by_reg = snd_shift_by_reg;
-	assign decode.snd_is_imm = snd_is_imm;
-	assign decode.shl = shl;
-	assign decode.shr = shr;
-	assign decode.ror = ror;
-	assign decode.put_carry = put_carry;
-	assign decode.sign_extend = sign_extend;
-	assign decode.imm = imm;
-	assign decode.shift_imm = shift_imm;
-
 	assign rn = insn `FIELD_DATA_RN;
 	assign rd = insn `FIELD_DATA_RD;
 	assign op = insn `FIELD_DATA_OPCODE;
-	assign r_snd = insn `FIELD_DATA_RM;
-	assign r_shift = insn `FIELD_DATA_RS;
-	assign imm = insn `FIELD_DATA_IMM8;
-	assign snd_is_imm = insn `FIELD_DATA_IMM;
-	assign snd_shift_by_reg = ~snd_is_imm & insn `FIELD_DATA_REGSHIFT;
-	assign undefined = snd_shift_by_reg & insn `FIELD_DATA_ZEROIFREG;
 
-	logic[1:0] shift_op;
-	assign shift_op = insn `FIELD_DATA_SHIFT;
+	assign snd_is_imm = insn `FIELD_DATA_IMM;
+	assign snd_shift_by_reg_if_reg = insn `FIELD_DATA_REGSHIFT;
 
 	always_comb begin
 		unique case(op)
@@ -60,41 +40,6 @@ module core_decode_data
 
 		if(restore_spsr)
 			update_flags = 0;
-
-		ror = snd_is_imm;
-		shr = ~snd_is_imm;
-		put_carry = 0;
-		sign_extend = 1'bx;
-
-		if(snd_is_imm)
-			shift_imm = {1'b0, insn `FIELD_DATA_ROR8, 1'b0};
-		else begin
-			shift_imm = {1'b0, insn `FIELD_DATA_SHIFTIMM};
-
-			case(shift_op)
-				`SHIFT_LSL: shr = 0;
-				`SHIFT_LSR: sign_extend = 0;
-				`SHIFT_ASR: sign_extend = 1;
-				`SHIFT_ROR: ;
-			endcase
-
-			if(~snd_shift_by_reg & (shift_imm == 0))
-				case(shift_op)
-					`SHIFT_LSL: ;
-
-					`SHIFT_LSR, `SHIFT_ASR:
-						shift_imm = 6'd32;
-
-					`SHIFT_ROR: begin
-						// RRX
-						shift_imm = 6'd1;
-						put_carry = 1;
-						sign_extend = 0;
-					end
-				endcase
-			else if(shift_op == `SHIFT_ROR)
-				ror = 1;
-		end
 	end
 
 endmodule
diff --git a/rtl/core/decode/decode.sv b/rtl/core/decode/decode.sv
index f7d7be8..f4de2d0 100644
--- a/rtl/core/decode/decode.sv
+++ b/rtl/core/decode/decode.sv
@@ -12,12 +12,12 @@ module core_decode
 	                   update_flags,
 	                   branch,
 	output ptr         branch_offset,
+	output snd_decode  snd_ctrl,
 	output data_decode data_ctrl
 );
 
 	logic cond_undefined;
 
-	//TODO
 	core_decode_conds conds
 	(
 		.cond(insn `FIELD_COND),
@@ -25,6 +25,18 @@ module core_decode
 		.*
 	);
 
+	logic snd_is_imm, snd_shift_by_reg_if_reg, snd_undefined;
+	snd_decode snd;
+
+	core_decode_snd snd_operand
+	(
+		.decode(snd),
+		.is_imm(snd_is_imm),
+		.shift_by_reg_if_reg(snd_shift_by_reg_if_reg),
+		.undefined(snd_undefined),
+		.*
+	);
+
 	logic branch_link;
 
 	core_decode_branch group_branch
@@ -37,7 +49,7 @@ module core_decode
 	//TODO
 	logic restore_spsr;
 
-	logic data_writeback, data_update_flags, data_undefined;
+	logic data_writeback, data_update_flags, data_is_imm, data_shift_by_reg_if_reg;
 	data_decode data;
 
 	core_decode_data group_data
@@ -45,7 +57,8 @@ module core_decode
 		.decode(data),
 		.writeback(data_writeback),
 		.update_flags(data_update_flags),
-		.undefined(data_undefined),
+		.snd_is_imm(data_is_imm),
+		.snd_shift_by_reg_if_reg(data_shift_by_reg_if_reg),
 		.*
 	);
 
@@ -57,6 +70,13 @@ module core_decode
 		update_flags = 0;
 		data_ctrl = {($bits(data_ctrl)){1'bx}};
 
+		snd_ctrl = {($bits(snd_ctrl)){1'bx}};
+		snd_ctrl.shl = 0;
+		snd_ctrl.shr = 0;
+		snd_ctrl.ror = 0;
+		snd_is_imm = 1'bx;
+		snd_shift_by_reg_if_reg = 1'bx;
+
 		priority casez(insn `FIELD_OP)
 			`GROUP_B: begin
 				branch = 1;
@@ -68,10 +88,15 @@ module core_decode
 			end
 
 			`GROUP_ALU: begin
+				snd_is_imm = data_is_imm;
+				snd_shift_by_reg_if_reg = data_shift_by_reg_if_reg;
+
+				snd_ctrl = snd;
 				data_ctrl = data;
+
 				writeback = data_writeback;
 				update_flags = data_update_flags;
-				undefined = undefined | data_undefined;
+				undefined = undefined | snd_undefined;
 			end
 
 			`INSN_MUL: ;
@@ -88,6 +113,7 @@ module core_decode
 				undefined = 1;
 				branch = 1'bx;
 				writeback = 1'bx;
+				snd_ctrl = {($bits(snd_ctrl)){1'bx}};
 			end
 		endcase
 	end
diff --git a/rtl/core/decode/snd.sv b/rtl/core/decode/snd.sv
new file mode 100644
index 0000000..5110d57
--- /dev/null
+++ b/rtl/core/decode/snd.sv
@@ -0,0 +1,77 @@
+`include "core/isa.sv"
+`include "core/uarch.sv"
+
+module core_decode_snd
+(
+	input  word       insn,
+	input  logic      is_imm,
+	                  shift_by_reg_if_reg,
+
+	output snd_decode decode,
+	output logic      undefined
+);
+
+	reg_num r, r_shift;
+	logic shift_by_reg, shl, shr, ror, put_carry, sign_extend;
+	logic[7:0] imm;
+	logic[5:0] shift_imm;
+
+	assign decode.r = r;
+	assign decode.r_shift = r_shift;
+	assign decode.shift_by_reg = shift_by_reg;
+	assign decode.is_imm = is_imm;
+	assign decode.shl = shl;
+	assign decode.shr = shr;
+	assign decode.ror = ror;
+	assign decode.put_carry = put_carry;
+	assign decode.sign_extend = sign_extend;
+	assign decode.imm = imm;
+	assign decode.shift_imm = shift_imm;
+
+	assign r = insn `FIELD_SND_RM;
+	assign r_shift = insn `FIELD_SND_RS;
+	assign imm = insn `FIELD_SND_IMM8;
+	assign shift_by_reg = ~is_imm & shift_by_reg_if_reg;
+	assign undefined = shift_by_reg & insn `FIELD_SND_ZEROIFREG;
+
+	logic[1:0] shift_op;
+	assign shift_op = insn `FIELD_SND_SHIFT;
+
+	always_comb begin
+		ror = is_imm;
+		shr = ~is_imm;
+		put_carry = 0;
+		sign_extend = 1'bx;
+
+		if(is_imm)
+			shift_imm = {1'b0, insn `FIELD_SND_ROR8, 1'b0};
+		else begin
+			shift_imm = {1'b0, insn `FIELD_SND_SHIFTIMM};
+
+			case(shift_op)
+				`SHIFT_LSL: shr = 0;
+				`SHIFT_LSR: sign_extend = 0;
+				`SHIFT_ASR: sign_extend = 1;
+				`SHIFT_ROR: ;
+			endcase
+
+			if(~shift_by_reg & (shift_imm == 0))
+				case(shift_op)
+					`SHIFT_LSL: ;
+
+					`SHIFT_LSR, `SHIFT_ASR:
+						shift_imm = 6'd32;
+
+					`SHIFT_ROR: begin
+						// RRX
+						shift_imm = 6'd1;
+						put_carry = 1;
+						sign_extend = 0;
+					end
+				endcase
+			else if(shift_op == `SHIFT_ROR)
+				ror = 1;
+		end
+	end
+
+endmodule