X-Git-Url: http://git.joshuawise.com/firearm.git/blobdiff_plain/7aa8541bb3a69361fcfe0e9b1148c693fd1043ec..1c2e57dc81bb31f2f577481bac788d279956dc39:/Issue.v

diff --git a/Issue.v b/Issue.v
index a450190..2df5bfa 100644
--- a/Issue.v
+++ b/Issue.v
@@ -2,7 +2,7 @@
 
 module Issue(
 	input clk,
-	input Nrst,
+	input Nrst,	/* XXX not used yet */
 	
 	input stall,	/* pipeline control */
 	input flush,
@@ -10,17 +10,16 @@ module Issue(
 	input inbubble,	/* stage inputs */
 	input [31:0] insn,
 	input [31:0] inpc,
+	input [31:0] cpsr,
 	
-	output reg outbubble,	/* stage outputs */
-	output reg [31:0] outpc
-	/* other */
+	output reg outstall = 0,	/* stage outputs */
+	output reg outbubble = 1,
+	output reg [31:0] outpc = 0,
+	output reg [31:0] outinsn = 0
+	/* XXX other? */
 	);
 	
-	always @(posedge clk)
-	begin
-		outbubble <= inbubble;
-		outpc <= inpc;
-	end
+
 
 `ifdef COPY_PASTA_FODDER
 	/* from page 2 of ARM7TDMIvE2.pdf */
@@ -230,4 +229,72 @@ module Issue(
 			def_regs = 16'bxxxxxxxxxxxxxxxx;
 		end
 		endcase
+	
+	/* Condition checking logic */
+	reg condition_met;
+	always @(*)
+		casez(insn[31:28])
+		`COND_EQ:	condition_met = cpsr[`CPSR_Z];
+		`COND_NE:	condition_met = !cpsr[`CPSR_Z];
+		`COND_CS:	condition_met = cpsr[`CPSR_C];
+		`COND_CC:	condition_met = !cpsr[`CPSR_C];
+		`COND_MI:	condition_met = cpsr[`CPSR_N];
+		`COND_PL:	condition_met = !cpsr[`CPSR_N];
+		`COND_VS:	condition_met = cpsr[`CPSR_V];
+		`COND_VC:	condition_met = !cpsr[`CPSR_V];
+		`COND_HI:	condition_met = cpsr[`CPSR_C] && !cpsr[`CPSR_Z];
+		`COND_LS:	condition_met = !cpsr[`CPSR_C] || cpsr[`CPSR_Z];
+		`COND_GE:	condition_met = cpsr[`CPSR_N] == cpsr[`CPSR_V];
+		`COND_LT:	condition_met = cpsr[`CPSR_N] != cpsr[`CPSR_V];
+		`COND_GT:	condition_met = !cpsr[`CPSR_Z] && (cpsr[`CPSR_N] == cpsr[`CPSR_V]);
+		`COND_LE:	condition_met = cpsr[`CPSR_Z] || (cpsr[`CPSR_N] != cpsr[`CPSR_V]);
+		`COND_AL:	condition_met = 1;
+		`COND_NV:	condition_met = 0;
+		default:	condition_met = 1'bx;
+		endcase
+	
+	/* Issue logic */
+`define STAGE_EXECUTE   0
+`define STAGE_MEMORY    1
+/* Once it's hit writeback, it's essentially hit the regfile so you're done. */
+	reg cpsr_inflight [1:0];
+	reg [15:0] regs_inflight [1:0];
+	
+	reg waiting_cpsr;
+	reg waiting_regs;
+	wire waiting = waiting_cpsr | waiting_regs;
+	
+	initial
+	begin
+		cpsr_inflight[0] = 0;
+		cpsr_inflight[1] = 0;
+		regs_inflight[0] = 0;
+		regs_inflight[1] = 0;
+	end
+		
+	always @(*)
+	begin
+		waiting_cpsr = use_cpsr & (cpsr_inflight[0] | cpsr_inflight[1]);
+		waiting_regs = |(use_regs & (regs_inflight[0] | regs_inflight[1]));
+		
+		outstall = waiting && !inbubble;	/* Happens in an always @*, because it is an exception. */
+	end
+	
+	/* Actually do the issue. */
+	always @(posedge clk)
+	begin
+		cpsr_inflight[0] <= cpsr_inflight[1];	/* I'm not sure how well selects work with arrays, and that seems like a dumb thing to get anusulated by. */
+		cpsr_inflight[1] <= (waiting || inbubble || !condition_met) ? 0 : def_cpsr;
+		regs_inflight[0] <= regs_inflight[1];
+		regs_inflight[1] <= (waiting || inbubble || !condition_met) ? 0 : def_regs;
+		
+		if (waiting)
+		begin
+			$display("ISSUE: Stalling instruction %08x because %d/%d", insn, waiting_cpsr, waiting_regs);
+		end
+
+		outbubble <= inbubble | waiting | !condition_met;
+		outpc <= inpc;
+		outinsn <= insn;
+	end
 endmodule