Add @let directive, start pondering interrupt control

17 files changed, 617 insertions, 158 deletions

diff --git a/asm/bootstrap.atk16 b/asm/bootstrap.atk16
new file mode 100644
index 0000000..c7ab63e
--- /dev/null
+++ b/asm/bootstrap.atk16
@@ -0,0 +1,23 @@
+@let stack_segment 0x8000
+@let vector_table  0x10
+
+@address vector_table
+  hlt_isr        ; 0x10 ISR0
+  hlt_isr        ; 0x11 ISR1
+  hlt_isr        ; 0x12 ISR2
+  hlt_isr        ; 0x13 ISR3
+  stack_segment  ; 0x14 Stack address
+
+@label hlt_isr
+  ldi 0x55 RA
+  hlt
+@label program_segment
+
+@address 0x0
+; set up stack pointer to point to beginning of stack segment
+  ldi 0x14 RA
+  ldr RA RF
+  jpi main
+
+@address program_segment
+; set up address for program code
diff --git a/asm/ext_std.py b/asm/ext_std.py
index 11da8aa..de7cd43 100644
--- a/asm/ext_std.py
+++ b/asm/ext_std.py
@@ -48,6 +48,9 @@ def expand_dec(reg: str) -> ExpandResult:
 def expand_mov(from_reg: str, to_reg: str) -> ExpandResult:
   return [["ali", "al_plus", from_reg, "0", to_reg]]
 
+def expand_nop() -> ExpandResult:
+  return [["ali", "al_plus", "RA", "0", "RA"]]
+
 def expand_spu(reg: str) -> ExpandResult:
   return [["str", reg, "__STACK_POINTER"]] + expand_inc("__STACK_POINTER")
 
@@ -89,6 +92,7 @@ expansions: OpExpansionDict = {
   "inc": expand_inc,
   "dec": expand_dec,
   "mov": expand_mov,
+  "nop": expand_nop,
   "spu": expand_spu,
   "spo": expand_spo,
   "csr": expand_csr,
diff --git a/asm/fibo.atk16 b/asm/fibo.atk16
index cae5f5d..fb375b3 100644
--- a/asm/fibo.atk16
+++ b/asm/fibo.atk16
@@ -2,17 +2,11 @@
 @opt csr_scratch RH
 @use ext_std:*
 
-; jump over data segment
-  jpi program
-
-; data segment
-@include ram_offset
-
-@label program
-; set up stack pointer to point to beginning of RAM
-  ldi ram_offset_addr RA
-  ldr RA RF
+; bootstrap code (must be called to setup mandatory data)
+; will jump to label main
+@include bootstrap
 
+@label main
 ; call fibo subroutine with parameter 10
   ldi 10 RA
   csi fibo
diff --git a/asm/ram_offset.atk16 b/asm/ram_offset.atk16
deleted file mode 100644
index e8c9255..0000000
--- a/asm/ram_offset.atk16
+++ /dev/null
@@ -1,2 +0,0 @@
-@label ram_offset_addr
-  0x8000
diff --git a/atk16-syntax/atk16-syntax-0.0.1.vsix b/atk16-syntax/atk16-syntax-0.0.1.vsix
index 342049e..253d326 100644
--- a/atk16-syntax/atk16-syntax-0.0.1.vsix
+++ b/atk16-syntax/atk16-syntax-0.0.1.vsix
diff --git a/atk16-syntax/extension.js b/atk16-syntax/extension.js
index 2c8e294..26b4d9d 100644
--- a/atk16-syntax/extension.js
+++ b/atk16-syntax/extension.js
@@ -85,9 +85,9 @@ class ATK16DefinitionProvider {
       }
     } else {
       const labelText = document.getText(range);
-      let labelLocation = await findLabelInDocument(document, labelText);
-      if (labelLocation) {
-        return labelLocation;
+      let definitionLocation = await findDefinitionInDocument(document, labelText);
+      if (definitionLocation) {
+        return definitionLocation;
       }
 
       // Search for labels in included files
@@ -104,9 +104,9 @@ class ATK16DefinitionProvider {
             const includedDocument = await vscode.workspace.openTextDocument(
               includedFilePath
             );
-            labelLocation = await findLabelInDocument(includedDocument, labelText);
-            if (labelLocation) {
-              return labelLocation;
+            definitionLocation = await findDefinitionInDocument(includedDocument, labelText);
+            if (definitionLocation) {
+              return definitionLocation;
             }
           }
         }
@@ -117,10 +117,10 @@ class ATK16DefinitionProvider {
   }
 }
 
-async function findLabelInDocument(document, labelText) {
+async function findDefinitionInDocument(document, labelText) {
   for (let i = 0; i < document.lineCount; i++) {
     const line = document.lineAt(i);
-    if (line.text.includes(`@label ${labelText}`)) {
+    if (line.text.includes(`@label ${labelText}`) || line.text.includes(`@let ${labelText}`)) {
       return new vscode.Location(document.uri, line.range.start);
     }
   }
diff --git a/atk16-syntax/package.json b/atk16-syntax/package.json
index 5fd48e6..6a64b6c 100644
--- a/atk16-syntax/package.json
+++ b/atk16-syntax/package.json
@@ -4,6 +4,8 @@
   "description": "Syntax highlighting and support for ATK16 assembly language",
   "version": "0.0.1",
   "publisher": "JanTuomi",
+  "license": "MIT",
+  "repository": "",
   "engines": {
     "vscode": "^1.60.0"
   },
diff --git a/atk16-syntax/syntaxes/atk16.tmLanguage.json b/atk16-syntax/syntaxes/atk16.tmLanguage.json
index b12f596..6dcf0ea 100644
--- a/atk16-syntax/syntaxes/atk16.tmLanguage.json
+++ b/atk16-syntax/syntaxes/atk16.tmLanguage.json
@@ -16,31 +16,23 @@
     },
     {
       "name": "variable.other.register.atk16",
-      "match": "R\\w+"
+      "match": "\\bR[A-H]\\b"
     },
     {
       "name": "constant.numeric.hex.atk16",
-      "match": "0x[0-9a-fA-F]+"
+      "match": "\\b0x[0-9a-fA-F]+\\b"
     },
     {
       "name": "constant.numeric.binary.atk16",
-      "match": "0b[01]+"
+      "match": "\\b0b[01]+\\b"
     },
     {
       "name": "constant.numeric.decimal.atk16",
-      "match": "[0-9]+"
+      "match": "\\b[0-9]+\\b"
     },
     {
-      "name": "entity.name.function.atk16",
-      "match": "\\w+(?=\\s*\\()"
-    },
-    {
-      "name": "entity.name.label.atk16",
-      "match": "\\w+(?=\\s*:)"
-    },
-    {
-      "name": "keyword.control.instruction.atk16",
-      "match": "^\\s+[a-zA-Z]+"
+      "name": "keyword.control.symbol.atk16",
+      "match": "^\\s+[a-zA-Z_-]+"
     },
     {
       "name": "constant.language.flag.atk16",
diff --git a/digital/atk16.dig b/digital/atk16.dig
index ca4aa6d..056fbb0 100644
--- a/digital/atk16.dig
+++ b/digital/atk16.dig
@@ -104,30 +104,6 @@
       <pos x="280" y="340"/>
     </visualElement>
     <visualElement>
-      <elementName>Driver</elementName>
-      <elementAttributes>
-        <entry>
-          <string>Bits</string>
-          <int>16</int>
-        </entry>
-      </elementAttributes>
-      <pos x="140" y="-240"/>
-    </visualElement>
-    <visualElement>
-      <elementName>Tunnel</elementName>
-      <elementAttributes>
-        <entry>
-          <string>rotation</string>
-          <rotation rotation="1"/>
-        </entry>
-        <entry>
-          <string>NetName</string>
-          <string>PC_OE</string>
-        </entry>
-      </elementAttributes>
-      <pos x="140" y="-260"/>
-    </visualElement>
-    <visualElement>
       <elementName>Tunnel</elementName>
       <elementAttributes>
         <entry>
@@ -258,7 +234,7 @@
       <elementAttributes>
         <entry>
           <string>rotation</string>
-          <rotation reference="../../../../visualElement[14]/elementAttributes/entry/rotation"/>
+          <rotation reference="../../../../visualElement[12]/elementAttributes/entry/rotation"/>
         </entry>
       </elementAttributes>
       <pos x="0" y="-180"/>
@@ -320,16 +296,6 @@
       <pos x="280" y="300"/>
     </visualElement>
     <visualElement>
-      <elementName>Probe</elementName>
-      <elementAttributes>
-        <entry>
-          <string>Label</string>
-          <string>Bus</string>
-        </entry>
-      </elementAttributes>
-      <pos x="200" y="-280"/>
-    </visualElement>
-    <visualElement>
       <elementName>atk16_mem.dig</elementName>
       <elementAttributes/>
       <pos x="580" y="-220"/>
@@ -993,7 +959,7 @@ program(0x4051, 0x40a2, 0x029b)
       <elementAttributes>
         <entry>
           <string>rotation</string>
-          <rotation reference="../../../../visualElement[77]/elementAttributes/entry/rotation"/>
+          <rotation reference="../../../../visualElement[74]/elementAttributes/entry/rotation"/>
         </entry>
       </elementAttributes>
       <pos x="740" y="740"/>
@@ -1031,6 +997,103 @@ program(0x4051, 0x40a2, 0x029b)
       <elementAttributes/>
       <pos x="680" y="-380"/>
     </visualElement>
+    <visualElement>
+      <elementName>atk16_irc.dig</elementName>
+      <elementAttributes/>
+      <pos x="160" y="-280"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Probe</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Label</string>
+          <string>Bus</string>
+        </entry>
+      </elementAttributes>
+      <pos x="320" y="-320"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Tunnel</elementName>
+      <elementAttributes>
+        <entry>
+          <string>rotation</string>
+          <rotation rotation="2"/>
+        </entry>
+        <entry>
+          <string>NetName</string>
+          <string>PC_OE</string>
+        </entry>
+      </elementAttributes>
+      <pos x="160" y="-200"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Tunnel</elementName>
+      <elementAttributes>
+        <entry>
+          <string>rotation</string>
+          <rotation reference="../../../../visualElement[4]/elementAttributes/entry/rotation"/>
+        </entry>
+        <entry>
+          <string>NetName</string>
+          <string>MAR_IE</string>
+        </entry>
+      </elementAttributes>
+      <pos x="160" y="-220"/>
+    </visualElement>
+    <visualElement>
+      <elementName>DipSwitch</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Label</string>
+          <string>IRQ0</string>
+        </entry>
+      </elementAttributes>
+      <pos x="-160" y="-480"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Ground</elementName>
+      <elementAttributes>
+        <entry>
+          <string>rotation</string>
+          <rotation rotation="1"/>
+        </entry>
+      </elementAttributes>
+      <pos x="-180" y="-460"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Ground</elementName>
+      <elementAttributes>
+        <entry>
+          <string>rotation</string>
+          <rotation reference="../../../../visualElement[85]/elementAttributes/entry/rotation"/>
+        </entry>
+      </elementAttributes>
+      <pos x="-180" y="-440"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Ground</elementName>
+      <elementAttributes>
+        <entry>
+          <string>rotation</string>
+          <rotation reference="../../../../visualElement[85]/elementAttributes/entry/rotation"/>
+        </entry>
+      </elementAttributes>
+      <pos x="-180" y="-420"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Splitter</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Input Splitting</string>
+          <string>1*4</string>
+        </entry>
+        <entry>
+          <string>Output Splitting</string>
+          <string>4</string>
+        </entry>
+      </elementAttributes>
+      <pos x="-140" y="-480"/>
+    </visualElement>
   </visualElements>
   <wires>
     <wire>
@@ -1070,6 +1133,10 @@ program(0x4051, 0x40a2, 0x029b)
       <p2 x="20" y="-260"/>
     </wire>
     <wire>
+      <p1 x="100" y="-260"/>
+      <p2 x="160" y="-260"/>
+    </wire>
+    <wire>
       <p1 x="40" y="260"/>
       <p2 x="60" y="260"/>
     </wire>
@@ -1111,6 +1178,10 @@ program(0x4051, 0x40a2, 0x029b)
     </wire>
     <wire>
       <p1 x="200" y="-140"/>
+      <p2 x="300" y="-140"/>
+    </wire>
+    <wire>
+      <p1 x="300" y="-140"/>
       <p2 x="480" y="-140"/>
     </wire>
     <wire>
@@ -1118,6 +1189,10 @@ program(0x4051, 0x40a2, 0x029b)
       <p2 x="200" y="-140"/>
     </wire>
     <wire>
+      <p1 x="-180" y="-460"/>
+      <p2 x="-140" y="-460"/>
+    </wire>
+    <wire>
       <p1 x="900" y="140"/>
       <p2 x="920" y="140"/>
     </wire>
@@ -1226,6 +1301,10 @@ program(0x4051, 0x40a2, 0x029b)
       <p2 x="20" y="-280"/>
     </wire>
     <wire>
+      <p1 x="120" y="-280"/>
+      <p2 x="160" y="-280"/>
+    </wire>
+    <wire>
       <p1 x="40" y="280"/>
       <p2 x="60" y="280"/>
     </wire>
@@ -1266,6 +1345,14 @@ program(0x4051, 0x40a2, 0x029b)
       <p2 x="920" y="220"/>
     </wire>
     <wire>
+      <p1 x="-160" y="-480"/>
+      <p2 x="-140" y="-480"/>
+    </wire>
+    <wire>
+      <p1 x="-120" y="-480"/>
+      <p2 x="120" y="-480"/>
+    </wire>
+    <wire>
       <p1 x="900" y="160"/>
       <p2 x="920" y="160"/>
     </wire>
@@ -1294,6 +1381,10 @@ program(0x4051, 0x40a2, 0x029b)
       <p2 x="540" y="-100"/>
     </wire>
     <wire>
+      <p1 x="-180" y="-420"/>
+      <p2 x="-140" y="-420"/>
+    </wire>
+    <wire>
       <p1 x="900" y="100"/>
       <p2 x="920" y="100"/>
     </wire>
@@ -1358,23 +1449,19 @@ program(0x4051, 0x40a2, 0x029b)
       <p2 x="780" y="300"/>
     </wire>
     <wire>
-      <p1 x="100" y="-240"/>
-      <p2 x="120" y="-240"/>
-    </wire>
-    <wire>
       <p1 x="-40" y="-240"/>
       <p2 x="20" y="-240"/>
     </wire>
     <wire>
-      <p1 x="160" y="-240"/>
-      <p2 x="200" y="-240"/>
-    </wire>
-    <wire>
       <p1 x="-280" y="-240"/>
       <p2 x="-220" y="-240"/>
     </wire>
     <wire>
-      <p1 x="200" y="-240"/>
+      <p1 x="260" y="-240"/>
+      <p2 x="300" y="-240"/>
+    </wire>
+    <wire>
+      <p1 x="300" y="-240"/>
       <p2 x="400" y="-240"/>
     </wire>
     <wire>
@@ -1410,6 +1497,10 @@ program(0x4051, 0x40a2, 0x029b)
       <p2 x="920" y="-120"/>
     </wire>
     <wire>
+      <p1 x="-180" y="-440"/>
+      <p2 x="-140" y="-440"/>
+    </wire>
+    <wire>
       <p1 x="900" y="120"/>
       <p2 x="920" y="120"/>
     </wire>
@@ -1446,18 +1537,14 @@ program(0x4051, 0x40a2, 0x029b)
       <p2 x="440" y="60"/>
     </wire>
     <wire>
-      <p1 x="200" y="-280"/>
-      <p2 x="200" y="-240"/>
+      <p1 x="300" y="-320"/>
+      <p2 x="320" y="-320"/>
     </wire>
     <wire>
       <p1 x="200" y="-40"/>
       <p2 x="200" y="80"/>
     </wire>
     <wire>
-      <p1 x="200" y="-240"/>
-      <p2 x="200" y="-140"/>
-    </wire>
-    <wire>
       <p1 x="200" y="-140"/>
       <p2 x="200" y="-80"/>
     </wire>
@@ -1543,7 +1630,7 @@ program(0x4051, 0x40a2, 0x029b)
     </wire>
     <wire>
       <p1 x="100" y="-280"/>
-      <p2 x="100" y="-240"/>
+      <p2 x="100" y="-260"/>
     </wire>
     <wire>
       <p1 x="40" y="280"/>
@@ -1558,6 +1645,14 @@ program(0x4051, 0x40a2, 0x029b)
       <p2 x="620" y="-100"/>
     </wire>
     <wire>
+      <p1 x="300" y="-320"/>
+      <p2 x="300" y="-240"/>
+    </wire>
+    <wire>
+      <p1 x="300" y="-240"/>
+      <p2 x="300" y="-140"/>
+    </wire>
+    <wire>
       <p1 x="-240" y="-340"/>
       <p2 x="-240" y="-220"/>
     </wire>
@@ -1582,6 +1677,10 @@ program(0x4051, 0x40a2, 0x029b)
       <p2 x="440" y="60"/>
     </wire>
     <wire>
+      <p1 x="120" y="-480"/>
+      <p2 x="120" y="-280"/>
+    </wire>
+    <wire>
       <p1 x="-60" y="-140"/>
       <p2 x="-60" y="-80"/>
     </wire>
diff --git a/digital/atk16_irc.dig b/digital/atk16_irc.dig
new file mode 100644
index 0000000..0037fa0
--- /dev/null
+++ b/digital/atk16_irc.dig
@@ -0,0 +1,341 @@
+<?xml version="1.0" encoding="utf-8"?>
+<circuit>
+  <version>2</version>
+  <attributes>
+    <entry>
+      <string>romContent</string>
+      <romList>
+        <roms/>
+      </romList>
+    </entry>
+    <entry>
+      <string>Width</string>
+      <int>5</int>
+    </entry>
+  </attributes>
+  <visualElements>
+    <visualElement>
+      <elementName>In</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Description</string>
+          <string>IRQ lines</string>
+        </entry>
+        <entry>
+          <string>Label</string>
+          <string>IRQ</string>
+        </entry>
+        <entry>
+          <string>Bits</string>
+          <int>4</int>
+        </entry>
+      </elementAttributes>
+      <pos x="140" y="480"/>
+    </visualElement>
+    <visualElement>
+      <elementName>In</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Description</string>
+          <string>PC value</string>
+        </entry>
+        <entry>
+          <string>Label</string>
+          <string>PC</string>
+        </entry>
+        <entry>
+          <string>Bits</string>
+          <int>16</int>
+        </entry>
+      </elementAttributes>
+      <pos x="140" y="400"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Splitter</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Input Splitting</string>
+          <string>4</string>
+        </entry>
+        <entry>
+          <string>Output Splitting</string>
+          <string>1*4</string>
+        </entry>
+      </elementAttributes>
+      <pos x="160" y="480"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Text</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Description</string>
+          <string>Some IRQ active?</string>
+        </entry>
+      </elementAttributes>
+      <pos x="140" y="440"/>
+    </visualElement>
+    <visualElement>
+      <elementName>In</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Label</string>
+          <string>MAR_IE</string>
+        </entry>
+      </elementAttributes>
+      <pos x="280" y="620"/>
+    </visualElement>
+    <visualElement>
+      <elementName>And</elementName>
+      <elementAttributes/>
+      <pos x="360" y="580"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Multiplexer</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Bits</string>
+          <int>16</int>
+        </entry>
+      </elementAttributes>
+      <pos x="460" y="400"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Out</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Label</string>
+          <string>DBUS</string>
+        </entry>
+        <entry>
+          <string>Bits</string>
+          <int>16</int>
+        </entry>
+      </elementAttributes>
+      <pos x="680" y="420"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Driver</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Bits</string>
+          <int>16</int>
+        </entry>
+        <entry>
+          <string>flipSelPos</string>
+          <boolean>true</boolean>
+        </entry>
+      </elementAttributes>
+      <pos x="600" y="420"/>
+    </visualElement>
+    <visualElement>
+      <elementName>In</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Label</string>
+          <string>PC_OE</string>
+        </entry>
+      </elementAttributes>
+      <pos x="580" y="540"/>
+    </visualElement>
+    <visualElement>
+      <elementName>PriorityEncoder</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Selector Bits</string>
+          <int>2</int>
+        </entry>
+      </elementAttributes>
+      <pos x="240" y="480"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Const</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Value</string>
+          <long>17</long>
+        </entry>
+        <entry>
+          <string>Bits</string>
+          <int>16</int>
+        </entry>
+      </elementAttributes>
+      <pos x="340" y="280"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Multiplexer</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Selector Bits</string>
+          <int>2</int>
+        </entry>
+        <entry>
+          <string>Bits</string>
+          <int>16</int>
+        </entry>
+      </elementAttributes>
+      <pos x="360" y="260"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Const</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Value</string>
+          <long>16</long>
+        </entry>
+        <entry>
+          <string>Bits</string>
+          <int>16</int>
+        </entry>
+      </elementAttributes>
+      <pos x="340" y="260"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Const</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Value</string>
+          <long>18</long>
+        </entry>
+        <entry>
+          <string>Bits</string>
+          <int>16</int>
+        </entry>
+      </elementAttributes>
+      <pos x="340" y="300"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Const</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Value</string>
+          <long>19</long>
+        </entry>
+        <entry>
+          <string>Bits</string>
+          <int>16</int>
+        </entry>
+      </elementAttributes>
+      <pos x="340" y="320"/>
+    </visualElement>
+    <visualElement>
+      <elementName>Testcase</elementName>
+      <elementAttributes>
+        <entry>
+          <string>Testdata</string>
+          <testData>
+            <dataString>IRQ    PC  MAR_IE PC_OE DBUS
+0b0000 0x5 0      0     Z
+0b0000 0x5 0      1     0x5
+0b0001 0x5 0	  1	0x5
+0b0001 0x5 1	  1     0x10
+0b0101 0x5 1      1     0x12</dataString>
+          </testData>
+        </entry>
+      </elementAttributes>
+      <pos x="640" y="240"/>
+    </visualElement>
+  </visualElements>
+  <wires>
+    <wire>
+      <p1 x="140" y="480"/>
+      <p2 x="160" y="480"/>
+    </wire>
+    <wire>
+      <p1 x="180" y="480"/>
+      <p2 x="240" y="480"/>
+    </wire>
+    <wire>
+      <p1 x="320" y="480"/>
+      <p2 x="380" y="480"/>
+    </wire>
+    <wire>
+      <p1 x="340" y="320"/>
+      <p2 x="360" y="320"/>
+    </wire>
+    <wire>
+      <p1 x="620" y="420"/>
+      <p2 x="680" y="420"/>
+    </wire>
+    <wire>
+      <p1 x="500" y="420"/>
+      <p2 x="580" y="420"/>
+    </wire>
+    <wire>
+      <p1 x="340" y="580"/>
+      <p2 x="360" y="580"/>
+    </wire>
+    <wire>
+      <p1 x="340" y="260"/>
+      <p2 x="360" y="260"/>
+    </wire>
+    <wire>
+      <p1 x="180" y="520"/>
+      <p2 x="240" y="520"/>
+    </wire>
+    <wire>
+      <p1 x="280" y="620"/>
+      <p2 x="360" y="620"/>
+    </wire>
+    <wire>
+      <p1 x="340" y="300"/>
+      <p2 x="360" y="300"/>
+    </wire>
+    <wire>
+      <p1 x="400" y="300"/>
+      <p2 x="440" y="300"/>
+    </wire>
+    <wire>
+      <p1 x="140" y="400"/>
+      <p2 x="460" y="400"/>
+    </wire>
+    <wire>
+      <p1 x="180" y="500"/>
+      <p2 x="240" y="500"/>
+    </wire>
+    <wire>
+      <p1 x="320" y="500"/>
+      <p2 x="340" y="500"/>
+    </wire>
+    <wire>
+      <p1 x="420" y="600"/>
+      <p2 x="480" y="600"/>
+    </wire>
+    <wire>
+      <p1 x="340" y="280"/>
+      <p2 x="360" y="280"/>
+    </wire>
+    <wire>
+      <p1 x="440" y="440"/>
+      <p2 x="460" y="440"/>
+    </wire>
+    <wire>
+      <p1 x="180" y="540"/>
+      <p2 x="240" y="540"/>
+    </wire>
+    <wire>
+      <p1 x="580" y="540"/>
+      <p2 x="600" y="540"/>
+    </wire>
+    <wire>
+      <p1 x="480" y="440"/>
+      <p2 x="480" y="600"/>
+    </wire>
+    <wire>
+      <p1 x="340" y="500"/>
+      <p2 x="340" y="580"/>
+    </wire>
+    <wire>
+      <p1 x="600" y="440"/>
+      <p2 x="600" y="540"/>
+    </wire>
+    <wire>
+      <p1 x="440" y="300"/>
+      <p2 x="440" y="440"/>
+    </wire>
+    <wire>
+      <p1 x="380" y="340"/>
+      <p2 x="380" y="480"/>
+    </wire>
+  </wires>
+  <measurementOrdering/>
+</circuit>
\ No newline at end of file
diff --git a/digital/atk16_mem.dig b/digital/atk16_mem.dig
index 15f080d..5c56552 100644
--- a/digital/atk16_mem.dig
+++ b/digital/atk16_mem.dig
@@ -67,10 +67,10 @@
         </entry>
         <entry>
           <string>Data</string>
-          <data>6001,8000,4001,2a00,400a,9e00,1fe0,3178,1b48,6001,f000,3148,1b48
-,3150,1b48,1011,860a,3158,1b48,4200,4401,650,1280,14c0,1009,8408
-,61fa,1b49,2540,1b49,2340,1b49,2f40,51c0,10c0,1b49,2740,1b49,2540
-,1b49,2340,1b49,2f40,51c0</data>
+          <data>4014,2a00,6014,13*8000,4*15,8000,4055,f000,400a,9e00,1fe0,3178
+,1b48,6001,f000,3148,1b48,3150,1b48,1011,860a,3158,1b48,4200,4401
+,650,1280,14c0,1009,8408,61fa,1b49,2540,1b49,2340,1b49,2f40,51c0
+,10c0,1b49,2740,1b49,2540,1b49,2340,1b49,2f40,51c0</data>
         </entry>
       </elementAttributes>
       <pos x="740" y="100"/>
diff --git a/src/asm_eval.py b/src/asm_eval.py
index 691e4eb..c05fc03 100644
--- a/src/asm_eval.py
+++ b/src/asm_eval.py
@@ -24,24 +24,24 @@ constants: dict[str, str] = {
   "sign": "3",
 }
 
-Labels = dict[str, int]
+Symbols = dict[str, int]
 
 def check_size(bits: int, val: int) -> None:
   if val >= 2 ** bits:
-    raise Exception(f"Value does not fit in {bits} bits: {val}")
+    raise Exception(f"Value does not fit in {bits} bits: 0x{val:>04x}")
 
-def eval_symbol(labels: Labels, c: str) -> str:
-  if c in labels:
-    return str(labels[c])
+def eval_symbol(symbols: Symbols, c: str) -> str:
+  if c in symbols:
+    return str(symbols[c])
 
   if c in constants:
     return constants[c]
 
   return c
 
-def eval_expr(labels: Labels, expr: str, bits: int = 16) -> int:
+def eval_expr(symbols: Symbols, expr: str, bits: int = 16) -> int:
   expr = expr.lower()
-  expr = eval_symbol(labels, expr)
-  ret = eval(expr, labels.copy()) # eval as Python expr
+  expr = eval_symbol(symbols, expr)
+  ret = eval(expr, symbols.copy()) # eval as Python expr
   check_size(bits, ret)
   return ret
diff --git a/src/asm_ops.py b/src/asm_ops.py
index 74e7930..61e2caa 100644
--- a/src/asm_ops.py
+++ b/src/asm_ops.py
@@ -11,12 +11,12 @@ class Options:
 class Meta:
   address: int
 
-def make_alr(meta: Meta, labels: Labels, alu_op: str, left: str, right: str, target: str) -> int:
+def make_alr(meta: Meta, symbols: Symbols, alu_op: str, left: str, right: str, target: str) -> int:
   """ALR 0000 TTTL LLRR RSSS"""
-  target_e = eval_expr(labels, target, bits=3)
-  left_e = eval_expr(labels, left, bits=3)
-  right_e = eval_expr(labels, right, bits=3)
-  alu_op_e = eval_expr(labels, alu_op, bits=3)
+  target_e = eval_expr(symbols, target, bits=3)
+  left_e = eval_expr(symbols, left, bits=3)
+  right_e = eval_expr(symbols, right, bits=3)
+  alu_op_e = eval_expr(symbols, alu_op, bits=3)
   word = (0b0000 << 12) + \
               (target_e << 9) + \
               (left_e << 6) + \
@@ -24,12 +24,12 @@ def make_alr(meta: Meta, labels: Labels, alu_op: str, left: str, right: str, tar
               alu_op_e
   return word
 
-def make_ali(meta: Meta, labels: Labels, alu_op: str, left: str, imm: str, target: str) -> int:
+def make_ali(meta: Meta, symbols: Symbols, alu_op: str, left: str, imm: str, target: str) -> int:
   """ALI 0001 TTTL LLII ISSS"""
-  target_e = eval_expr(labels, target, bits=3)
-  left_e = eval_expr(labels, left, bits=3)
-  imm_e = eval_expr(labels, imm, bits=3)
-  alu_op_e = eval_expr(labels, alu_op, bits=3)
+  target_e = eval_expr(symbols, target, bits=3)
+  left_e = eval_expr(symbols, left, bits=3)
+  imm_e = eval_expr(symbols, imm, bits=3)
+  alu_op_e = eval_expr(symbols, alu_op, bits=3)
   word = (0b0001 << 12) + \
               (target_e << 9) + \
               (left_e << 6) + \
@@ -37,62 +37,64 @@ def make_ali(meta: Meta, labels: Labels, alu_op: str, left: str, imm: str, targe
               alu_op_e
   return word
 
-def make_ldr(meta: Meta, labels: Labels, addr_reg: str, to_reg: str) -> int:
+def make_ldr(meta: Meta, symbols: Symbols, addr_reg: str, to_reg: str) -> int:
   """LDR 0010 TTTR RRXX XXXX"""
-  to_reg_e = eval_expr(labels, to_reg, bits=3)
-  addr_reg_e = eval_expr(labels, addr_reg, bits=3)
+  to_reg_e = eval_expr(symbols, to_reg, bits=3)
+  addr_reg_e = eval_expr(symbols, addr_reg, bits=3)
   word = (0b0010 << 12) + \
               (to_reg_e << 9) + \
               (addr_reg_e << 6)
   return word
 
-def make_str(meta: Meta, labels: Labels, from_reg: str, addr_reg: str) -> int:
+def make_str(meta: Meta, symbols: Symbols, from_reg: str, addr_reg: str) -> int:
   """STR 0011 XXXL LLRR RXXX"""
-  from_reg_e = eval_expr(labels, from_reg, bits=3)
-  addr_reg_e = eval_expr(labels, addr_reg, bits=3)
+  from_reg_e = eval_expr(symbols, from_reg, bits=3)
+  addr_reg_e = eval_expr(symbols, addr_reg, bits=3)
   word = (0b0011 << 12) + \
               (addr_reg_e << 6) + \
               (from_reg_e << 3)
   return word
 
-def make_ldi(meta: Meta, labels: Labels, imm: str, to_reg: str) -> int:
+def make_ldi(meta: Meta, symbols: Symbols, imm: str, to_reg: str) -> int:
   """LDI 0100 TTTI IIII IIII"""
-  to_reg_e = eval_expr(labels, to_reg, bits=3)
-  imm_e = eval_expr(labels, imm, bits=9)
+  to_reg_e = eval_expr(symbols, to_reg, bits=3)
+  imm_e = eval_expr(symbols, imm, bits=9)
   word = (0b0100 << 12) + \
               (to_reg_e << 9) + \
               imm_e
   return word
 
-def make_jpr(meta: Meta, labels: Labels, addr_reg: str) -> int:
+def make_jpr(meta: Meta, symbols: Symbols, addr_reg: str) -> int:
   """JPR 0101 XXXR RRXX XXXX"""
-  addr_reg_e = eval_expr(labels, addr_reg, bits=3)
+  addr_reg_e = eval_expr(symbols, addr_reg, bits=3)
   word = (0b0101 << 12) + \
               (addr_reg_e << 6)
   return word
 
-def make_jpi(meta: Meta, labels: Labels, imm: str) -> int:
+def make_jpi(meta: Meta, symbols: Symbols, imm: str) -> int:
   """JPI 0110 XXXI IIII IIII"""
-  imm_e = eval_expr(labels, imm, bits=9)
+  imm_e = eval_expr(symbols, imm, bits=9)
   imm_e = imm_e - meta.address - 1
   imm_e = imm_e & (0b111111111)
+  print("symbols:", symbols)
+  print(meta, imm, f"0x{imm_e:>0x}")
   word = (0b0110 << 12) + \
               imm_e
   return word
 
-def make_brr(meta: Meta, labels: Labels, flag_s: str, addr_reg: str) -> int:
+def make_brr(meta: Meta, symbols: Symbols, flag_s: str, addr_reg: str) -> int:
   """brr  0111 XFFR RRXX XXXX"""
-  flag_s_e = eval_expr(labels, flag_s, bits=2)
-  addr_reg_e = eval_expr(labels, addr_reg, bits=3)
+  flag_s_e = eval_expr(symbols, flag_s, bits=2)
+  addr_reg_e = eval_expr(symbols, addr_reg, bits=3)
   word = (0b0111 << 12) + \
               (flag_s_e << 9) + \
               (addr_reg_e << 6)
   return word
 
-def make_bri(meta: Meta, labels: Labels, flag_s: str, imm: str) -> int:
+def make_bri(meta: Meta, symbols: Symbols, flag_s: str, imm: str) -> int:
   """BRI 1000 XFFI IIII IIII"""
-  flag_s_e = eval_expr(labels, flag_s, bits=2)
-  imm_e = eval_expr(labels, imm, bits=9)
+  flag_s_e = eval_expr(symbols, flag_s, bits=2)
+  imm_e = eval_expr(symbols, imm, bits=9)
   imm_e = imm_e - meta.address - 1
   imm_e = imm_e & (0b111111111)
   word = (0b1000 << 12) + \
@@ -100,14 +102,14 @@ def make_bri(meta: Meta, labels: Labels, flag_s: str, imm: str) -> int:
               imm_e
   return word
 
-def make_lpc(meta: Meta, labels: Labels, target: str) -> int:
+def make_lpc(meta: Meta, symbols: Symbols, target: str) -> int:
   """LPC 1001 TTTX XXXX XXXX"""
-  target_e = eval_expr(labels, target, bits=3)
+  target_e = eval_expr(symbols, target, bits=3)
   word = (0b1001 << 12) + \
               (target_e << 9)
   return word
 
-def make_hlt(meta: Meta, labels: Labels) -> int:
+def make_hlt(meta: Meta, symbols: Symbols) -> int:
   """HLT 1111 XXXX XXXX XXXX"""
   word = (0b1111 << 12)
   return word
diff --git a/src/asm_pass0.py b/src/asm_pass0.py
index a0ae56d..4913e4b 100644
--- a/src/asm_pass0.py
+++ b/src/asm_pass0.py
@@ -12,13 +12,9 @@ class Result0Line:
 @dataclass
 class Result0:
   lines: list[Result0Line]
-  options: Options
-  operations: OpExpansionDict
 
 def pass_0(lines: list[str], file_name: str) -> Result0:
-  options = Options()
   result_lines: list[Result0Line] = []
-  operations: OpExpansionDict = default_expansions.copy()
 
   for (line_num, line) in enumerate(lines):
     line = line.split(";")[0].strip()
@@ -29,12 +25,15 @@ def pass_0(lines: list[str], file_name: str) -> Result0:
         asm_file_name = args[0]
         path = os.path.join(os.path.dirname(file_name), asm_file_name + ".atk16")
         with open(path, "r") as f:
-          for incl_line in f.readlines():
-            result_lines.append(Result0Line(
-              src_file=asm_file_name,
-              line_num=line_num,
-              line=incl_line
-            ))
+          incl_lines = f.readlines()
+
+        incl_result0 = pass_0(incl_lines, asm_file_name)
+        for incl_line in incl_result0.lines:
+          result_lines.append(Result0Line(
+            src_file=incl_line.src_file,
+            line_num=incl_line.line_num,
+            line=incl_line.line
+          ))
 
       case _:
         result_lines.append(Result0Line(
@@ -44,7 +43,5 @@ def pass_0(lines: list[str], file_name: str) -> Result0:
         ))
 
   return Result0(
-    operations=operations,
-    options=options,
     lines=result_lines
   )
diff --git a/src/asm_pass3.py b/src/asm_pass3.py
index 76e7b84..5221f6d 100644
--- a/src/asm_pass3.py
+++ b/src/asm_pass3.py
@@ -16,21 +16,24 @@ class Result3:
   lines: list[Result3Line]
   options: Options
   operations: OpExpansionDict
-  labels: dict[str, int]
+  symbols: dict[str, int]
 
 def pass_3(result2: Result2) -> Result3:
   result_lines: list[Result3Line] = []
-  labels: dict[str, int] = {}
+  symbols: dict[str, int] = {}
   address = 0
 
   for line in result2.lines:
     keyword, *args = line.parts
     match keyword:
       case "@address":
-        address = eval(args[0])
+        address = eval_expr(symbols, args[0])
         continue
       case "@label":
-        labels[args[0]] = address
+        symbols[args[0]] = address
+        continue
+      case "@let":
+        symbols[args[0]] = eval_expr(symbols, args[1])
         continue
       case _:
         result_lines.append(Result3Line(
@@ -42,9 +45,16 @@ def pass_3(result2: Result2) -> Result3:
         ))
         address += 1
 
+  result_lines.sort(key=lambda l: l.address)
+  for result_line in result_lines:
+    rows_with_same_addr = list(filter(lambda l: l.address == result_line.address, result_lines))
+    n = len(rows_with_same_addr)
+    if n > 1:
+      formatted = "\n".join(map(lambda l: " ".join(l.parts), rows_with_same_addr))
+      raise Exception(f"Overlapping segments: address 0x{result_line.address:>04x} has conflicting definitions:\n{formatted}")
   return Result3(
     operations=result2.operations,
     options=result2.options,
     lines=result_lines,
-    labels=labels,
+    symbols=symbols,
   )
diff --git a/src/asm_pass4.py b/src/asm_pass4.py
index dc65b65..462707a 100644
--- a/src/asm_pass4.py
+++ b/src/asm_pass4.py
@@ -17,7 +17,7 @@ class Result4:
   lines: list[Result4Line]
   options: Options
   operations: OpExpansionDict
-  labels: dict[str, int]
+  symbols: dict[str, int]
 
 def translate_opt(arg: str, options: Options) -> str:
   match arg:
@@ -27,12 +27,11 @@ def translate_opt(arg: str, options: Options) -> str:
 
 def pass_4(result3: Result3) -> Result4:
   result_lines: list[Result4Line] = []
-  address = 0
 
   for line in result3.lines:
     keyword, *args = line.parts
     meta = Meta(
-      address=address,
+      address=line.address,
     )
 
     args = list(map(lambda a: translate_opt(a, result3.options), args))
@@ -41,7 +40,7 @@ def pass_4(result3: Result3) -> Result4:
 
     if keyword in operations:
       fn = operations[keyword]
-      word = fn(meta, result3.labels, *args)
+      word = fn(meta, result3.symbols, *args)
       result_lines.append(Result4Line(
         line_num=line.line_num,
         src_file=line.src_file,
@@ -56,18 +55,16 @@ def pass_4(result3: Result3) -> Result4:
           line_num=line.line_num,
           src_file=line.src_file,
           address=line.address,
-          word=eval_expr(result3.labels, keyword),
+          word=eval_expr(result3.symbols, keyword),
           text=text,
           original_text=original_text,
         ))
       except:
         raise Exception(f"Invalid assembly at {line.src_file}:{line.line_num + 1}\n\n{line}")
 
-    address += 1
-
   return Result4(
     operations=result3.operations,
-    labels=result3.labels,
+    symbols=result3.symbols,
     options=result3.options,
     lines=result_lines,
   )
diff --git a/src/assembler.py b/src/assembler.py
index 8f84288..c678ba0 100755
--- a/src/assembler.py
+++ b/src/assembler.py
@@ -62,9 +62,9 @@ result = bytearray()
 result.extend(nop)
 
 for line in result4.lines:
-  for (label, label_addr) in result4.labels.items():
-    if line.address == label_addr:
-      print(f"{label}:")
+  for (symbol, symbol_value) in result4.symbols.items():
+    if line.address == symbol_value:
+      print(f"{symbol}:")
 
   if len(result) < 2 * line.address + 1:
     result.extend((2 * line.address + 1 - len(result)) * nop)