From 484293ae7865bf10d8bdb9c5c70982c57acfc0c9 Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Sun, 28 Mar 2021 15:31:00 -0700
Subject: Some more interesting opcodes.

---
 hdl/top.sv | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

(limited to 'hdl')

diff --git a/hdl/top.sv b/hdl/top.sv
index 8524b63..aa5a4e2 100644
--- a/hdl/top.sv
+++ b/hdl/top.sv
@@ -43,6 +43,7 @@ bit [DATA_BITS-1:0] pc;
 bit [3:0] opcode;
 bit [7:0] operand;
 bit [DATA_BITS-1:0] acc;
+bit [DATA_BITS-1:0] idx;
 
 enum
     {   FETCH
@@ -56,6 +57,7 @@ always_ff @(posedge clk) begin
         tx_data = 0;
         pc = 0;
         acc = 0;
+        idx = 0;
         state = state.first;
     end else begin
         if (`tx_ready) tx_valid = 0;
@@ -68,18 +70,31 @@ always_ff @(posedge clk) begin
             end
 
             DECODE: begin
+                //$display("%x %x:%x (acc=%x idx=%x)", pc, opcode, operand, acc, idx);
                 state = FETCH;
                 case (opcode)
-                    'b000: acc = {{4{operand[7]}}, operand};
-                    'b001: begin
-                        if (tx_valid) begin
-                            state = DECODE;
-                        end else begin
-                            tx_valid = 1;
-                            tx_data = acc[7:0];
+                    'h0: acc = {{4{operand[7]}}, operand};
+                    'h1: acc = mem[idx + operand];
+                    'h2: mem[idx + operand] = acc;
+                    'h3: if (acc != operand) ++pc;
+                    'h4: pc = pc + {{4{operand[7]}}, operand};
+                    'hf: begin
+                        if (operand[0]) ++acc;
+                        if (operand[1]) --acc;
+                        if (operand[2]) ++idx;
+                        if (operand[3]) --idx;
+                        if (operand[4]) {idx, acc} = {acc, idx};
+                        if (operand[5]) idx = acc;
+                        if (operand[6]) begin
+                            if (tx_valid) begin
+                                state = DECODE;
+                            end else begin
+                                tx_valid = 1;
+                                tx_data = acc[7:0];
+                            end
                         end
+                        if (operand[7]) state = DECODE;
                     end
-                    'b111: state = DECODE;
                 endcase
             end
         endcase
-- 
cgit v1.2.3