Remove idx, add indirect jumps, renumber opcodes so NOP=0, add absolute labels to asm.rb

3 files changed, 133 insertions, 117 deletions

diff --git a/asm.rb b/asm.rb
index c3a0125..4883edb 100755
--- a/asm.rb
+++ b/asm.rb
@@ -2,20 +2,17 @@
 
 OPCODES = {
   "i"     => 0x080,
-  "acc="  => 0x000,
-  "ladd"  => 0x100,
-  "store" => 0x200,
-  "ifeq"  => 0x300,
-  "jmp"   => 0x400,
-  "ascii" => 0x500,
-  "++acc" => 0xf01,
-  "--acc" => 0xf02,
-  "++idx" => 0xf04,
-  "--idx" => 0xf08,
-  "swap"  => 0xf10,
-  "idx"   => 0xf20,
-  "tx"    => 0xf40,
-  "halt"  => 0xf80,
+  "acc="  => 0x100,
+  "ladd"  => 0x200,
+  "store" => 0x300,
+  "ifeq"  => 0x400,
+  "jmp"   => 0x500,
+  "ascii" => 0x600,
+  "cla"   => 0x001,
+  "++acc" => 0x002,
+  "--acc" => 0x004,
+  "tx"    => 0x040,
+  "halt"  => 0x080,
   }
 
 Line = Struct.new(:opcode, :refs, :code)
@@ -56,9 +53,11 @@ end
 $code.each_with_index() do | line, i |
   op = line.opcode
   line.refs.each() do | ref |
-    if $labels.key?(ref)
+    if ref =~ /^@(.+)$/ and $labels.key?($1)
+      op |= $labels[$1]
+    elsif $labels.key?(ref)
       target = $labels[ref] - (i + 1)
-      target += 0x100 if target < 0
+      target += 0x80 if target < 0
       op |= target
     else
       throw "I don't understand #{ref.inspect()}"
diff --git a/hdl/top.sv b/hdl/top.sv
index 00d0cab..71a5a48 100644
--- a/hdl/top.sv
+++ b/hdl/top.sv
@@ -68,7 +68,6 @@ 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;
 
 bit [ADDR_BITS-1:0] address;
 bit [DATA_BITS-1:0] sign_extended_operand;
@@ -91,10 +90,9 @@ always_ff @(posedge clk) begin
         tx_data = 0;
         pc = 0;
         acc = 0;
-        idx = 0;
         state = state.first;
     end else begin
-        `ifdef DEBUG $display("s=%0d pc=%x (acc=%x idx=%x) (mem %b:%x)", state, pc, acc, idx, `mem_read_valid, `mem_read_data); `endif
+        `ifdef DEBUG $display("s=%0d pc=%x (acc=%x) (mem %b:%x)", state, pc, acc, `mem_read_valid, `mem_read_data); `endif
         if (`tx_ready) tx_valid = 0;
 
         case (state)
@@ -118,29 +116,33 @@ always_ff @(posedge clk) begin
                     sign_extended_operand = {{(DATA_BITS-8){operand[7]}}, operand};
                     `ifdef DEBUG $display("\tdecode %x:%x", opcode, operand); `endif
                     case (opcode)
-                        'h0: acc = sign_extended_operand;
-                        'h1, 'h2: begin
+                        'h0: begin
+                            if (operand[0]) acc = 0;
+                            if (operand[1]) ++acc;
+                            if (operand[2]) --acc;
+                            if (operand[6]) state = MEMORY;
+                            if (operand[7]) state = HALT;
+                        end
+                        'h1: acc = sign_extended_operand;
+                        'h2, 'h3: begin
                             address = {7'b0, operand[6:0]};
                             state = operand[7] ? INDIRECT : AGEN;
                         end
-                        'h3: if (acc != sign_extended_operand) ++pc;
-                        'h4: pc = pc + sign_extended_operand;
+                        'h4: if (acc != sign_extended_operand) ++pc;
                         'h5: begin
+                            if (operand[7]) begin
+                                address = {7'b0, operand[6:0]};
+                                state = INDIRECT;
+                            end else begin
+                                pc = pc + {{(ADDR_BITS-7){operand[6]}}, operand[6:0]};
+                            end
+                        end
+                        'h6: begin
                             mem_write_data = acc % 10 + 'h30;
                             acc = acc / 10;
                             address = {7'b0, operand[6:0]};
                             state = operand[7] ? INDIRECT : AGEN;
                         end
-                        '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]) state = MEMORY;
-                            if (operand[7]) state = HALT;
-                        end
                     endcase
                 end
             end
@@ -169,21 +171,22 @@ always_ff @(posedge clk) begin
                 state = FETCH;
                 `ifdef DEBUG $display("\tagen"); `endif
                 case (opcode)
-                    'h1: begin
+                    'h2: begin
                         mem_valid = 1;
-                        mem_address = address + idx;
+                        mem_address = address;
                         state = `mem_ready ? MEMORY : AGEN;
                     end
-                    'h2: begin
+                    'h3: begin
                         mem_valid = 1;
-                        mem_address = address + idx;
+                        mem_address = address;
                         mem_write = 1;
                         mem_write_data = acc;
                         state = `mem_ready ? FETCH : AGEN;
                     end
-                    'h5: begin
+                    'h5: pc = address;
+                    'h6: begin
                         mem_valid = 1;
-                        mem_address = address + idx;
+                        mem_address = address;
                         mem_write = 1;
                         state = `mem_ready ? FETCH : AGEN;
                     end
@@ -198,14 +201,7 @@ always_ff @(posedge clk) begin
                 state = FETCH;
                 `ifdef DEBUG $display("\tstall"); `endif
                 case (opcode)
-                    'h1: begin
-                        if (`mem_read_valid) begin
-                            acc = acc + `mem_read_data;
-                        end else begin
-                            state = MEMORY;
-                        end
-                    end
-                    'hf: begin
+                    'h0: begin
                         if (operand[6]) begin
                             if (tx_valid) begin
                                 state = MEMORY;
@@ -215,6 +211,13 @@ always_ff @(posedge clk) begin
                             end
                         end
                     end
+                    'h2: begin
+                        if (`mem_read_valid) begin
+                            acc = acc + `mem_read_data;
+                        end else begin
+                            state = MEMORY;
+                        end
+                    end
                 endcase
             end
 
diff --git a/mem/mem.hex b/mem/mem.hex
index 07023a8..4d5700f 100644
--- a/mem/mem.hex
+++ b/mem/mem.hex
@@ -1,76 +1,90 @@
 @0
 
-// Reset state is acc=0 idx=0
+10d // acc= @fib       # for the toy indirect jump to fib
+369 // store 0x69
+170 // acc= 0x70
+36a // store 0x6a
+001 // loop: cla
+2ea // ladd i 0x6a
+400 // ifeq 0
+5e9 // jmp i 0x69       # toy indirect jump to fib
+040 // tx
+003 // cla ++acc
+26a // ladd 0x6a
+36a // store 0x6a
+577 // jmp loop
+36a // fib: store 0x6a  # zero, it is known
+370 // store 0x70       # 0x70 is now beginning of Fibonacci sequence (0)
+003 // cla ++acc
+371 // store 0x71       # 0x71 is 1
+170 // fibloop: acc= 0x70
+26a // ladd 0x6a
+369 // store 0x69
+001 // cla
+2e9 // ladd i 0x69      # next fib number to print
+66b // ascii 0x6b       # LSB of ASCII rep
+66c // ascii 0x6c
+66d // ascii 0x6d
+66e // ascii 0x6e       # MSB of ASCII rep
+104 // acc= 4
+369 // store 0x69
+005 // scan: cla --acc
+269 // ladd 0x69
+4ff // ifeq -1
+508 // jmp print
+369 // store 0x69
+16b // acc= 0x6b
+269 // ladd 0x69
+368 // store 0x68
+001 // cla
+2e8 // ladd i 0x68
+430 // ifeq 0x30
+574 // jmp scan
+16b // print: acc= 0x6b
+269 // ladd 0x69
+368 // store 0x68
+001 // cla
+2e8 // ladd i 0x68
+040 // tx
+005 // cla --acc
+269 // ladd 0x69
+4ff // ifeq -1
+502 // jmp space
+369 // store 0x69
+574 // jmp print
+120 // space: acc= 0x20
+040 // tx
+170 // acc= 0x70
+26a // ladd 0x6a
+369 // store 0x69
+003 // cla ++acc
+269 // ladd 0x69        # compute &fib[i+1]
+368 // store 0x68
+003 // cla ++acc
+268 // ladd 0x68        # compute &fib[i+2]
+367 // store 0x67
+001 // cla
+2e9 // ladd i 0x69
+2e8 // ladd i 0x68      # compute fib[i+2]
+3e7 // store i 0x67     # store it
+003 // cla ++acc
+26a // ladd 0x6a
+432 // ifeq 50
+502 // jmp fullydone
+36a // store 0x6a
+548 // jmp fibloop
+121 // fullydone: acc= 0x21
+040 // tx
+080 // halt
 
-000 // loop: acc= 0     # Print from 0x70 until we find a 0x00 byte
-170 // ladd i 0x6a
-300 // ifeq 0
-402 // jmp fib
-f44 // ++idx tx
-4fa // jmp loop
-f20 // fib: idx         # N.B. acc is 0 at this point (we got here from ifeq 0)
-270 // store 0x70       # 0x70 is now beginning of Fibonacci sequence (0)
-001 // acc= 1
-271 // store 0x71       # 0x71 is 1
-000 // fibloop: acc= 0
-f10 // swap
-332 // ifeq 50
-42b // jmp fullydone
-26f // store 0x6f       # 0x6f is current index into Fibonacci sequence
-f10 // swap
-170 // ladd 0x70        # Load next unprinted number in Fibonacci sequence
-f10 // swap
-000 // acc= 0
-f10 // swap
-56b // ascii 0x6b       # LSB of ASCII rep
-56c // ascii 0x6c
-56d // ascii 0x6d
-56e // ascii 0x6e       # MSB of ASCII rep
-004 // acc= 4
-f10 // swap
-f08 // scan: --idx
-000 // acc= 0
-16b // ladd 0x6b
-f10 // swap
-300 // ifeq 0
-412 // jmp allzeroes
-f10 // swap
-330 // ifeq 0x30
-4f7 // jmp scan
-f40 // done: tx
-f10 // swap
-300 // ifeq 0
-404 // jmp space
-f12 // --acc swap
-000 // acc= 0
-16b // ladd 0x6b
-4f8 // jmp done
-020 // space: acc= 0x20
-f40 // tx
-000 // acc= 0
-f20 // idx
-16f // ladd 0x6f
-f10 // swap
-402 // jmp nextfib
-f10 // allzeroes: swap
-4ef // jmp done
-170 // nextfib: ladd 0x70   # Load just-printed Fibonacci number
-171 // ladd 0x71            # Add about-to-print Fibonacci number
-272 // store 0x72           # Store n+2 Fibonacci number
-f04 // ++idx
-4d1 // jmp fibloop
-021 // fullydone: acc= 0x21
-f40 // tx
-f80 // halt
-
-@6a
-
-070 // 6a: constant 0x070
-000 // 6b: LSB of ASCII rep
-000 // 6c: USB of ASCII rep
-000 // 6d: USB of ASCII rep
-000 // 6e: MSB of ASCII rep
-000 // 6f: next index to store in memory image of Fibonacci sequence
+// 67: scratch (pointer to fib[i+2])
+// 68: scratch (pointer to fib[i+1])
+// 69: scratch (pointer to fib[i]) (j)
+// 6a: i
+// 6b: LSB of ASCII rep
+// 6c: USB of ASCII rep
+// 6d: USB of ASCII rep
+// 6e: MSB of ASCII rep
 
 @70