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.

---
 Makefile    |  2 +-
 hdl/top.sv  | 31 +++++++++++++++++++++++--------
 mem/mem.hex | 55 +++++++++++++++++++++++++++++++++++++++----------------
 3 files changed, 63 insertions(+), 25 deletions(-)

diff --git a/Makefile b/Makefile
index f4a0da8..24e2692 100644
--- a/Makefile
+++ b/Makefile
@@ -9,7 +9,7 @@ sim: build/Vtop
 
 build/Vtop: $(SOURCES) $(COLLATERAL)
 	@mkdir -p build
-	verilator +1800-2017ext+sv -Wall -Wno-BLKSEQ -Wno-UNUSED -O3 -Ihdl $(OPTS) --Mdir build --trace --cc --build -j --exe --top-module top $(SOURCES)
+	verilator +1800-2017ext+sv -Wall -Wno-BLKSEQ -Wno-UNUSED -Wno-WIDTH -O3 -Ihdl $(OPTS) --Mdir build --trace --cc --build -j --exe --top-module top $(SOURCES)
 
 clean:
 	rm -rf build
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
diff --git a/mem/mem.hex b/mem/mem.hex
index 6d096bb..7923fb7 100644
--- a/mem/mem.hex
+++ b/mem/mem.hex
@@ -1,18 +1,41 @@
 @0
 
-048 100 // H
-065 100 // e
-06c 100 // l
-06c 100 // l
-06f 100 // o
-02c 100 // ,
-020 100 // ' '
-077 100 // w
-06f 100 // o
-072 100 // r
-06c 100 // l
-064 100 // d
-021 100 // !
-00a 100 // \n
-
-700
+040 // %acc = 0x40
+f20 // %idx = %acc
+
+// loop: (addr 2)
+100     // %acc = [%idx]
+300 402 // if (%acc == 0) { %pc = exit }
+f44     // ++%idx; tx %acc
+4fb     // jmp loop
+// exit: (addr 7)
+
+f80 // hcf
+
+@40
+
+048 // H
+065 // e
+06c // l
+06c // l
+06f // o
+02c // ,
+020 // ' '
+077 // w
+06f // o
+072 // r
+06c // l
+064 // d
+021 // !
+00a // \n
+
+000
+
+04f // O
+06f // o
+070 // p
+073 // s
+021 // !
+00a // \n
+
+000
-- 
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