From a1daa4c4b3d7972325b67dd1770264cbc9b95f5e Mon Sep 17 00:00:00 2001
From: TQ Hirsch <thequux@thequux.com>
Date: Thu, 31 Aug 2023 13:46:28 +0200
Subject: [PATCH] Fully implemented CPU and memory busses, but not yet tested

---
 .idea/gradle.xml                              |   1 +
 .idea/vcs.xml                                 |   6 +
 doc/pdp10-impl.adoc                           |  11 +
 doc/peripheral-map.txt                        |  73 ++
 .../com/thequux/mcpdp/core/AddressSpace.kt    |  29 +-
 src/main/kotlin/com/thequux/mcpdp/core/CPU.kt | 670 ++++++++++++++----
 .../kotlin/com/thequux/mcpdp/core/HaltInsn.kt |   5 +
 .../com/thequux/mcpdp/core/MemoryError.kt     |   9 +
 .../com/thequux/mcpdp/core/PagingUnit.kt      | 206 ++++++
 .../com/thequux/mcpdp/peripheral/MemBus.kt    |  58 ++
 .../com/thequux/mcpdp/peripheral/Unibus.kt    |  71 ++
 .../thequux/mcpdp/util/ConfigurationError.kt  |   4 +
 .../com/thequux/mcpdp/util/ProgrammerError.kt |   4 +
 13 files changed, 1019 insertions(+), 128 deletions(-)
 create mode 100644 .idea/vcs.xml
 create mode 100644 doc/pdp10-impl.adoc
 create mode 100644 doc/peripheral-map.txt
 create mode 100644 src/main/kotlin/com/thequux/mcpdp/core/HaltInsn.kt
 create mode 100644 src/main/kotlin/com/thequux/mcpdp/core/MemoryError.kt
 create mode 100644 src/main/kotlin/com/thequux/mcpdp/core/PagingUnit.kt
 create mode 100644 src/main/kotlin/com/thequux/mcpdp/peripheral/MemBus.kt
 create mode 100644 src/main/kotlin/com/thequux/mcpdp/peripheral/Unibus.kt
 create mode 100644 src/main/kotlin/com/thequux/mcpdp/util/ConfigurationError.kt
 create mode 100644 src/main/kotlin/com/thequux/mcpdp/util/ProgrammerError.kt

diff --git a/.idea/gradle.xml b/.idea/gradle.xml
index f9163b4..ce1c62c 100644
--- a/.idea/gradle.xml
+++ b/.idea/gradle.xml
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="GradleMigrationSettings" migrationVersion="1" />
   <component name="GradleSettings">
     <option name="linkedExternalProjectsSettings">
       <GradleProjectSettings>
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
new file mode 100644
index 0000000..94a25f7
--- /dev/null
+++ b/.idea/vcs.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/doc/pdp10-impl.adoc b/doc/pdp10-impl.adoc
new file mode 100644
index 0000000..2d0fb6a
--- /dev/null
+++ b/doc/pdp10-impl.adoc
@@ -0,0 +1,11 @@
+# Basic model
+
+This emulates a PDP-11/70 with some changes
+
+# Privilege levels
+
+There is an additional "executive" privilege level
+
+# Available peripheral page addrs
+
+EAE is not implemented; thus 777300/5 is available
\ No newline at end of file
diff --git a/doc/peripheral-map.txt b/doc/peripheral-map.txt
new file mode 100644
index 0000000..6a4bc9a
--- /dev/null
+++ b/doc/peripheral-map.txt
@@ -0,0 +1,73 @@
+# D <Name> <Description>
+# A <base>/<prefix>
+# R <addr> <name> <desc>
+# F <size of floating window, in bytes (oct)>
+
+D ROM
+A 3000/3
+
+D CD11 Card reader
+A 2460/9
+R 2460 CDST Status and control register
+R 2462 CDCC Column count register
+R 2464 CDBA Current address register
+R 2466 CDDB Data buffer register
+
+D CR11/CM11 Card reader
+R 7160 CRS Status register
+R 7162 CRB1 Data buffer register 1
+R 7164 CRB2 Data buffer register 2
+
+D DH11 16-line serial multiplexer
+F 20
+R 00 DHSCR System control register
+R 02 DHNRC Next received character
+R 04 DHLPR Line parameter register
+R 06 DHCAR Current address register
+R 10 DHBCR Byte count register
+R 12 DHBAR Buffer active register
+R 14 DHBRK Break control register
+R 16 DHSIL Silo status register
+
+D DJ11 16-line serial multiplexer
+F 10
+R 00 DJCSR Control status register
+R 02 DJRBUF Receive buffer
+R 04 DJTCR Transmitter control
+R 04 DJBCR Break control register
+R 06 DJTBUF Transmit buffer
+
+D DL11 1-line serial interface (console)
+A 7560/9
+F 10
+R 0 RCSR Receive status register
+R 2 RBUF Receive data buffer
+R 4 XCST Transmit status register
+R 6 XBUF Transmit buffer
+
+D DMC11 Network link
+F 10
+
+D DN11 Automatic calling unit
+A 5200/5 (1 word each)
+
+D DQ11 NPR Synchronous line interface
+F 10
+R 0 RXSTAT Receive status register
+R 2 TXSTAT Transmit status register
+R 4 REGERR Reg/Err register
+R 6 SECREG Secondary register
+
+D DR11-B DMA controller
+A 2410/9
+R 2410 DRWC Word count
+R 2412 DRBA Bus address
+R 2414 DRST Status and command
+R 2416 DRDB Data buffer
+
+D PC11 Paper tape reader/punch
+A 7550/
+R 7550 PRS Reader status register
+R 7552 PRB Reader buffer
+R 7554 PPB Punch status
+R 7556 PPB Punch buffer
\ No newline at end of file
diff --git a/src/main/kotlin/com/thequux/mcpdp/core/AddressSpace.kt b/src/main/kotlin/com/thequux/mcpdp/core/AddressSpace.kt
index e59ae42..b861091 100644
--- a/src/main/kotlin/com/thequux/mcpdp/core/AddressSpace.kt
+++ b/src/main/kotlin/com/thequux/mcpdp/core/AddressSpace.kt
@@ -1,8 +1,31 @@
 package com.thequux.mcpdp.core
 
-interface AddressSpace {
-    fun getw(addr: UShort): UShort
+import com.thequux.mcpdp.ext.bit.bic
+import com.thequux.mcpdp.ext.bit.bit
+import com.thequux.mcpdp.ext.bit.shl
+import com.thequux.mcpdp.ext.bit.shr
+
+interface VAddressSpace {
+    fun getw(addr: UShort, dspace: Boolean = false): UShort
     fun getb(addr: UShort): UByte
-    fun setw(addr: UShort, value: UShort)
+    fun setw(addr: UShort, value: UShort, dspace: Boolean = false)
     fun setb(addr: UShort, value: UByte)
+}
+
+// Implements the full 22-bit physical address space.
+// Odd addresses accessed through word instructions are a bus fault; this is handled by the main memory map
+interface PAddressSpace {
+    fun getw(addr: UInt): UShort
+    fun getb(addr: UInt): UByte = (getw(addr bic 0) shr (if (addr bit 0) 8 else 0)).toUByte()
+    fun setw(addr: UInt, value: UShort)
+    fun setb(addr: UInt, value: UByte) {
+        val waddr = addr bic 0
+        val load = getw(waddr)
+        val store = if (addr bit 0) {
+            load and 0xFF00u or value.toUShort()
+        } else {
+            load and 0x00FFu or (value.toUShort() shl 8)
+        }
+        setw(waddr, store)
+    }
 }
\ No newline at end of file
diff --git a/src/main/kotlin/com/thequux/mcpdp/core/CPU.kt b/src/main/kotlin/com/thequux/mcpdp/core/CPU.kt
index b4c7527..c5a2cb8 100644
--- a/src/main/kotlin/com/thequux/mcpdp/core/CPU.kt
+++ b/src/main/kotlin/com/thequux/mcpdp/core/CPU.kt
@@ -1,6 +1,8 @@
 package com.thequux.mcpdp.core
 
 import com.thequux.mcpdp.ext.bit.*
+import com.thequux.mcpdp.peripheral.MemBus
+import com.thequux.mcpdp.util.ProgrammerError
 
 /// The main CPU
 ///
@@ -9,14 +11,73 @@ import com.thequux.mcpdp.ext.bit.*
 /// Exxx: ROM
 /// xxxx: rest
 @OptIn(ExperimentalUnsignedTypes::class)
-class CPU(private val core: AddressSpace) {
+class CPU(private val mbus: MemBus) {
     private val registers = UShortArray(8)
-    public var psw: UShort = 0U
+    private val general_registers = Array<UShortArray>(2) { UShortArray(5) }
+    private val shadow_r6 = UShortArray(4) //
+    private val core = PagingUnit(mbus)
+
+    var runState: RunState = RunState.HALTED
+    var psw: UShort
+        get() {
+            var res = 0
+            if (C) res = res or 0x0001
+            if (V) res = res or 0x0002
+            if (Z) res = res or 0x0004
+            if (N) res = res or 0x0008
+            if (T) res = res or 0x0010
+            res = res or (psw_pl shl 5)
+            res = res or (cur_mode shl 14) or (prv_mode shl 12)
+            res = res or (registerSet shl 11)
+            return res.toUShort()
+        }
+        set(value) {
+            var newpsw = value.toInt()
+            C = value bit 1
+            V = value bit 2
+            Z = value bit 3
+            N = value bit 4
+            T = value bit 5 // TODO: handle suspended trap
+            psw_pl = newpsw shr 5 and 7
+            registerSet = newpsw shr 11 and 1
+            cur_mode = newpsw shr 14
+
+        }
+
+    private var cur_mode: Int = 0
+        set(value) {
+            prv_mode = field
+            shadow_r6[field] = sp
+            field = if (value == 2) 3 else value
+            sp = shadow_r6[field]
+            core.mode = value
+        }
+    private var prv_mode: Int = 0
+    private var psw_pl: Int = 0
     private var pc: UShort
         get() = registers[7]
         set(value) {
             registers[7] = value
         }
+    private var sp: UShort
+        get() = registers[6]
+        set(value) {
+            registers[6] = value
+        }
+
+    private var registerSet: Int = 0
+        set(value) {
+            if (value !in 0..1) {
+                throw ProgrammerError("Invalid register set number")
+            }
+            val old = general_registers[field]
+            val new = general_registers[value]
+            for (i in 0..5) {
+                old[i] = registers[i]
+                registers[i] = new[i]
+            }
+            field = value
+        }
 
     private var cc: UShort
         get() = psw and 0xFu
@@ -28,14 +89,25 @@ class CPU(private val core: AddressSpace) {
     private var C: Boolean = false
     private var Z: Boolean = false
     private var V: Boolean = false
+    private var T: Boolean = false
+    private val PADDR_REG_BIT: Int = 23
 
-    /// Load an operand. This performs any indicated pre-inc/post-dec, so this or op_adjust must be called exactly once per operand
+    init {
+        val regs = Registers()
+        mbus.unibus.run {
+            attach(0x3FFF8u, 3, regs)
+            attach(0x3FFF4u, 2, regs)
+        }
+        core.mount(mbus.unibus)
+    }
+
+    private fun is_paddr_reg(addr: UInt): Boolean = addr bit PADDR_REG_BIT
     private fun op_resolve(operand: Int, byte_mode: Boolean = false): UInt {
         val mode = operand shr 3
         val reg = operand and 0x7
         val increment = if (byte_mode && reg != 7) 1U else 2U
-        return when (mode) {
-            0 -> reg.toUInt() + 0x1_0000U
+        return when (mode and 0x7) {
+            0 -> reg.toUInt() bis PADDR_REG_BIT
             1 -> registers[reg].toUInt()
             2 -> {
                 val addr = registers[reg]
@@ -65,14 +137,13 @@ class CPU(private val core: AddressSpace) {
                 pc = (pc+2u).toUShort()
                 core.getw((idx+registers[reg]).toUShort()).toUInt()
             }
-            else -> throw InvalidOpcodeException()
+            else -> throw InvalidOpcodeException() // unreachable
         }
     }
 
-    /// Store an operand. This assumes that the spec has already been `load`ed or `adjust`ed
     private fun op_storb(spec: UInt, value: UByte) {
         val addr = (spec and 0xFFFFu).toUShort()
-        if (spec >= 0x1_0000u) {
+        if (is_paddr_reg(spec)) {
             // register
             registers[addr.toInt()] = registers[addr.toInt()] and 0xFF00u or value.toUShort()
         } else {
@@ -82,40 +153,42 @@ class CPU(private val core: AddressSpace) {
 
     private fun op_loadb(spec: UInt): UByte {
         val addr = (spec and 0xFFFFu).toUShort()
-        return if (spec > 0x1_0000u) {
+        return if (is_paddr_reg(spec)) {
             (registers[addr.toInt()] and 0xFFu).toUByte()
         } else {
             core.getb(addr)
         }
     }
 
-    private fun op_storw(spec: UInt, value: UShort) {
+    private fun op_storw(spec: UInt, value: UShort, dspace: Boolean = true) {
         val addr = (spec and 0xFFFFu).toUShort()
-        if (spec >= 0x1_0000u) {
+        if (is_paddr_reg(spec)) {
             // register
             registers[addr.toInt()] = value
         } else {
-            core.setw(addr, value)
+            core.setw(addr, value, dspace)
         }
     }
 
-    private fun op_loadw(spec: UInt): UShort {
+    private fun op_loadw(spec: UInt, dspace: Boolean=true): UShort {
         val addr = (spec and 0xFFFFu).toUShort()
-        return if (spec > 0x1_0000u) {
+        return if (is_paddr_reg(spec)) {
             (registers[addr.toInt()] and 0xFFu)
         } else {
-            core.getw(addr)
+            core.getw(addr, dspace)
         }
     }
 
-    companion object {
-        val CC_C: UShort = 1U
-        val CC_V: UShort = 2U
-        val CC_Z: UShort = 4U
-        val CC_N: UShort = 8U
-    }
     private fun opc_dst(opcode: Int): UInt = op_resolve(opcode and 0x3F)
+    private fun opc_dstb(opcode: Int): UInt = op_resolve(opcode and 0x3F, byte_mode = true)
     private fun opc_src(opcode: Int): UInt = op_resolve(opcode shr 6 and 0xFC0)
+    private fun opc_srcb(opcode: Int): UInt = op_resolve(opcode shr 6 and 0xFC0, byte_mode = true)
+
+    private fun stack_pop(): UShort = core.getw(sp).also { sp = (sp + 2u).toUShort() }
+    private fun stack_push(value: UShort) {
+        sp = (sp-2u).toUShort()
+        core.setw(sp, value)
+    }
 
     private fun br_rel(cond: Boolean, opcode: Int) {
         if (cond) {
@@ -126,103 +199,345 @@ class CPU(private val core: AddressSpace) {
         val opcode = core.getw(pc).toInt()
         pc = (pc + 2u).toUShort()
         when (opcode and 0xF000) {
-            0x0, 0x8000 -> when (opcode and 0xFFC0) {
-                0x0000 -> when (opcode) {
-                    0x0003 -> throw Trap(14) // BPT
+            0x0, 0x8000 -> when (opcode and 0xFF00) {
+                0x0000 ->  when (opcode) {
+                    0x0000 -> runState = RunState.HALTED
+                    0x0001 -> runState = RunState.WAIT_FOR_INTERRUPT
+                    0x0002 -> { // RTI
+                        pc = stack_pop()
+                        psw = stack_pop() // TODO: check privilege on mode; check psw[11]
+                    } // RTI
+                    0x0003 -> trap(0x0Cu) // BPT
+                    0x0004 -> trap(0x10u) // IOT
+                    0x0005 -> throw InvalidOpcodeException() // bus reset TODO: bus init
+                    0x0006 -> {
+                        // TODO: handle suspending the trace trap
+                        pc = stack_pop()
+                        psw = stack_pop()
+                    } // RTT
+                    in 0x40..0x7f -> {
+                        // jmp
+                        val dst = opc_dst(opcode)
+                        if (is_paddr_reg(dst)) {
+                            throw InvalidOpcodeException()
+                        }
+                        pc = dst.toUShort()
+                    } // JMP
+                    in 0x80..0x87 -> {
+                        val reg = opcode and 0x7
+                        pc = registers[reg]
+                        registers[reg] = stack_pop()
+                    } // RTS
+                    in 0x98..0x9F -> {
+                        psw_pl = opcode and 0x7
+                    } // SPL
+                    in 0xA0..0xBF -> {
+                        val flag = opcode bit 4
+                        if (opcode bit 0) C = flag
+                        if (opcode bit 1) V = flag
+                        if (opcode bit 2) Z = flag
+                        if (opcode bit 3) N = flag
+                    } // Scc/Ccc
+                    in 0xC0..0xFF -> {
+                        val dst = opc_dst(opcode)
+                        val v = op_loadw(dst)
+                        val res = (v shl 8) or (v shr 8)
+                        op_storw(dst, res)
+                        V = false
+                        C = false
+                        N = res bit 7
+                        Z = (res and 0xFFu) == 0.toUShort()
+                    } // SWAB
+                    else -> throw InvalidOpcodeException()
                 }
-                0x0080 ->
-                0x0100, 0x0140, 0x0180, 0x01C0 -> br_rel(true, opcode) // BR
-                0x0200, 0x0240, 0x0280, 0x02C0 -> br_rel(!Z, opcode) // BNE
-                0x0300, 0x0340, 0x0380, 0x03C0 -> br_rel(Z, opcode) // BEQ
-                0x0400, 0x0440, 0x0480, 0x04C0 -> br_rel(N == V, opcode) // BGE
-                0x0600, 0x0640, 0x0680, 0x06C0 -> br_rel(!Z and (N == V), opcode) // BGT
-                0x0500, 0x0540, 0x0580, 0x05C0 -> br_rel(N xor V, opcode) // BLT
-                0x0700, 0x0740, 0x0780, 0x07C0 -> br_rel(Z or (N xor V), opcode) // BLE
+                0x0100 -> br_rel(true, opcode) // BR
+                0x0200 -> br_rel(!Z, opcode) // BNE
+                0x0300 -> br_rel(Z, opcode) // BEQ
+                0x0400 -> br_rel(N == V, opcode) // BGE
+                0x0500 -> br_rel(N xor V, opcode) // BLT
+                0x0600 -> br_rel(!Z and (N == V), opcode) // BGT
+                0x0700 -> br_rel(Z or (N xor V), opcode) // BLE
+                0x0800, 0x0900 -> { // JSR
+                    val r = opcode shr 6 and 0x7
+                    val dst = op_loadw(opc_dst(r))
+                    stack_push(registers[r])
+                    registers[r] = pc
+                    pc = dst
+                } // JSR
+                0x0A00 -> when (opcode shr 6 and 3) {
+                    0 -> { // CLR
+                        op_storw(opc_dst(opcode), 0U)
+                        N = false
+                        V = false
+                        C = false
+                        Z = true
+                    } // CLR
+                    1 -> { // COM
+                        val dst = opc_dst(opcode)
+                        val res = op_loadw(dst).inv().also { op_storw(dst, it) }
+                        N = res bit 15
+                        Z = res == 0U.toUShort()
+                        C = true
+                        V = false
+                    } // COM
+                    2 -> { // INC
+                        val dst = opc_dst(opcode)
+                        val res = op_loadw(dst).inc().also { op_storw(dst, it) }
+                        N = res bit 15
+                        Z = res == 0.toUShort()
+                        V = res == 0x8000.toUShort()
+                    } // INC
+                    3 -> { // DEC
+                        val dst = opc_dst(opcode)
+                        val res = op_loadw(dst).dec().also { op_storw(dst, it) }
+                        N = res bit 15
+                        Z = res == 0.toUShort()
+                        V = res == 0x7FFF.toUShort()
+                    } // DEC
+                }
+                0x0B00 -> when (opcode shr 6 and 3) {
+                    0 -> { // NEG
+                        val dst = opc_dst(opcode)
+                        val res = op_loadw(dst).inv().inc()
+                        op_storw(dst, res)
+                        N = res bit 15
+                        Z = res == 0.toUShort()
+                        V = res == 0x8000.toUShort()
+                        C = !Z
+                    } // NEG
+                    1 -> { // ADC
+                        val dst = opc_dst(opcode)
+                        val c: UShort = if (C) 1u else 0u
+                        val res = (op_loadw(dst) + c).toUShort()
+                        op_storw(dst, res)
+                        N = res bit 15
+                        Z = res == 0u.toUShort()
+                        V = (res == 0x8000u.toUShort()) and C
+                        C = Z and C
+                    } // ADC
+                    2 -> {
+                        val dst = opc_dst(opcode)
+                        val src = op_loadw(dst)
+                        val res = if (C) src.dec() else src
+                        op_storw(dst, res)
+                        N = res bit 15
+                        Z = res == 0.toUShort()
+                        V = res == 0x8000.toUShort()
+                        C = C and (src == 0.toUShort())
+                    } // SBC
+                    3 -> {
+                        val dst = op_loadw(opc_dst(opcode))
+                        Z = dst == 0.toUShort()
+                        N = dst bit 15
+                        V = false
+                        C = false
+                    } // TST
+                }
+                0x0C00 -> when (opcode shr 6 and 3) {
+                    0 -> {
+                        val dst = opc_dst(opcode)
+                        val src = op_loadw(dst)
+                        val res = (src shr 1).bit(15, C)
+                        op_storw(dst, res)
+                        C = src bit 0
+                        N = res bit 15
+                        Z = res == 0.toUShort()
+                        V = N xor C
+                    } // ROR
+                    1 -> {
+                        val dst = opc_dst(opcode)
+                        val src = op_loadw(dst)
+                        val res = (src shl 1).bit(0, C)
+                        op_storw(dst, res)
+                        C = src bit 15
+                        N = res bit 15
+                        Z = res == 0.toUShort()
+                        V = N xor C
+                    } // ROL
+                    2 -> { // ASR
+                        val dst = opc_dst(opcode)
+                        val src = op_loadw(dst).toShort()
+                        val res = (src shr 1).toUShort()
+                        op_storw(dst, res)
+                        N = res bit 15
+                        Z = res == 0.toUShort()
+                        C = src bit 0
+                        V = N xor C
+                    } // ASR
+                    3 -> { // ASL
+                        val dst = opc_dst(opcode)
+                        val src = op_loadw(dst)
+                        val res = src shl 1
+                        op_storw(dst, res.toUShort())
+                        N = res bit 15
+                        Z = res == 0.toUShort()
+                        C = src and 0x8000u != 0u.toUShort()
+                        V = N xor C
+                    } // ASL
+                }
+                0x0D00 -> when (opcode shr 6 and 3) {
+                    0 -> { // MARK
+                        val count = opcode and 0x3F
+                        sp = (sp + (2 * count).toUInt()).toUShort()
+                        pc = registers[5]
+                        registers[5] = stack_pop()
+                    } // MARK
+                    1 -> { throw InvalidOpcodeException() } // MFPI // TODO
+                    2 -> { throw InvalidOpcodeException() } // MTPI // TODO
+                    3 -> {
+                        op_storw(opc_dst(opcode), if (N) 0.toUShort() else (-1).toUShort())
+                        Z = !N
+                        V = false
+                    } // SXT
+                }
+                0x0F00 -> throw InvalidOpcodeException() // CSM
+                0x8000 -> br_rel(!N, opcode) // BPL
+                0x8100 -> br_rel(N, opcode) // BMI
+                0x8200 -> br_rel(!C and !Z, opcode) // BHI
+                0x8300 -> br_rel(C or Z, opcode) // BLOS
+                0x8400 -> br_rel(!V, opcode) // BVC
+                0x8500 -> br_rel(V, opcode) // BVS
+                0x8600 -> br_rel(!C, opcode) // BCC/BHIS
+                0x8700 -> br_rel(C, opcode) // BCS/BLO
+                0x8800 -> trap(0x18u) // EMT
+                0x8900 -> trap(0x1Cu) // TRAP
 
-                0x0A00 -> { // CLR
-                    op_storw(opc_dst(opcode), 0U)
-                    N = false
-                    V = false
-                    C = false
-                    Z = true
-                } // CLR
-                0x0B40 -> { // ADC
-                    val dst = opc_dst(opcode)
-                    val c: UShort = if (C) 1u else 0u
-                    val res = (op_loadw(dst) + c).toUShort()
-                    op_storw(dst, res)
-                    N = res bit 15
-                    Z = res == 0u.toUShort()
-                    V = (res == 0x8000u.toUShort()) and C
-                    C = Z and C
-                } // ADC
-                0x0C80 -> { // ASR
-                    val dst = opc_dst(opcode)
-                    val src = op_loadw(dst).toShort()
-                    val res = (src shr 1).toUShort()
-                    op_storw(dst, res)
-                    N = res bit 15
-                    Z = res == 0.toUShort()
-                    C = src bit 0
-                    V = N xor C
-                } // ASR
-                0x0CC0 -> { // ASL
-                    val dst = opc_dst(opcode)
-                    val src = op_loadw(dst)
-                    val res = src shl 1
-                    op_storw(dst, res.toUShort())
-                    N = res bit 15
-                    Z = res == 0.toUShort()
-                    C = src and 0x8000u != 0u.toUShort()
-                    V = N xor C
-                } // ASL
-                0x8000, 0x8040, 0x8080, 0x80C0 -> br_rel(!N, opcode) // BPL
-                0x8100, 0x8140, 0x8180, 0x81C0 -> br_rel(N, opcode) // BMI
-                0x8200, 0x8240, 0x8280, 0x82C0 -> br_rel(!C and !Z, opcode) // BHI
-                0x8300, 0x8340, 0x8380, 0x83C0 -> br_rel(C or Z, opcode) // BLOS
-                0x8400, 0x8440, 0x8480, 0x84C0 -> br_rel(!V, opcode) // BVC
-                0x8500, 0x8540, 0x8580, 0x85C0 -> br_rel(V, opcode) // BVS
-                0x8600, 0x8640, 0x8680, 0x86C0 -> br_rel(!C, opcode) // BCC/BHIS
-                0x8700, 0x8740, 0x8780, 0x87C0 -> br_rel(C, opcode) // BCS/BLO
-
-                0x8A00 -> { // CLRB
-                    op_storb(opc_dst(opcode), 0U)
-                    N = false
-                    V = false
-                    C = false
-                    Z = true
-                } // CLRB
-                0x8B40 -> { // ADCB
-                    val dst = opc_dst(opcode)
-                    val c: UShort = if (C) 1u else 0u
-                    val res = (op_loadb(dst) + c).toUByte()
-                    op_storb(dst, res)
-                    N = res bit 7
-                    Z = res == 0u.toUByte()
-                    V = (res == 0x80u.toUByte()) and C
-                    C = Z and C
-                } // ADCB
-                0x8C80 -> { // ASRB
-                    val dst = opc_dst(opcode)
-                    val src = op_loadb(dst).toByte()
-                    val res = (src shr 1).toUByte()
-                    op_storb(dst, res)
-                    N = res bit 7
-                    Z = res == 0.toUByte()
-                    C = src bit 0
-                    V = N xor C
-                } // ASRB
-                0x8CC0 -> { // ASLB
-                    val dst = opc_dst(opcode)
-                    val src = op_loadb(dst)
-                    val res = (src shl 1).toUByte()
-                    op_storw(dst, res.toUShort())
-                    N = res bit 7
-                    Z = res == 0.toUByte()
-                    C = src bit 7
-                    V = N xor C
-                } // ASLB
+                0x8A00 -> when (opcode shr 6 and 3) {
+                    0 -> { // CLRB
+                        op_storb(opc_dstb(opcode), 0U)
+                        N = false
+                        V = false
+                        C = false
+                        Z = true
+                    } // CLRB
+                    1 -> { // COMB
+                        val dst = opc_dstb(opcode)
+                        val res = op_loadb(dst).inv().also { op_storb(dst, it) }
+                        N = res bit 7
+                        Z = res == 0U.toUByte()
+                        C = true
+                        V = false
+                    } // COMB
+                    2 -> { // INC
+                        val dst = opc_dstb(opcode)
+                        val res = op_loadb(dst).inc().also { op_storb(dst, it) }
+                        N = res bit 7
+                        Z = res == 0.toUByte()
+                        V = res == 0x80.toUByte()
+                    } // INC
+                    3 -> { // DEC
+                        val dst = opc_dstb(opcode)
+                        val res = op_loadb(dst).dec().also { op_storb(dst, it) }
+                        N = res bit 7
+                        Z = res == 0.toUByte()
+                        V = res == 0x7F.toUByte()
+                    } // DEC
+                }
+                0x8B00 -> when (opcode shr 6 and 3) {
+                    0 -> { // NEGB
+                        val dst = opc_dstb(opcode)
+                        val res = op_loadb(dst).inv().inc()
+                        op_storb(dst, res)
+                        N = res bit 7
+                        Z = res == 0.toUByte()
+                        V = res == 0x8000.toUByte()
+                        C = !Z
+                    } // NEGB
+                    1 -> { // ADCB
+                        val dst = opc_dstb(opcode)
+                        val c: UShort = if (C) 1u else 0u
+                        val res = (op_loadb(dst) + c).toUByte()
+                        op_storb(dst, res)
+                        N = res bit 7
+                        Z = res == 0u.toUByte()
+                        V = (res == 0x80u.toUByte()) and C
+                        C = Z and C
+                    } // ADCB
+                    2 -> {
+                        val dst = opc_dstb(opcode)
+                        val src = op_loadb(dst)
+                        val res = if (C) src.dec() else src
+                        op_storb(dst, res)
+                        N = res bit 8
+                        Z = res == 0.toUByte()
+                        V = res == 0x80.toUByte()
+                        C = C and (src == 0.toUByte())
+                    } // SBCB
+                    3 -> {
+                        val dst = op_loadb(opc_dstb(opcode))
+                        Z = dst == 0.toUByte()
+                        N = dst bit 7
+                        V = false
+                        C = false
+                    } // TSTB
+                }
+                0x8C00 -> when (opcode shr 6 and 3) {
+                    0 -> {
+                        val dst = opc_dstb(opcode)
+                        val src = op_loadb(dst)
+                        val res = (src shr 1).bit(7, C)
+                        op_storb(dst, res)
+                        C = src bit 0
+                        N = res bit 7
+                        Z = res == 0.toUByte()
+                        V = N xor C
+                    } // RORB
+                    1 -> {
+                        val dst = opc_dstb(opcode)
+                        val src = op_loadb(dst)
+                        val res = (src shl 1).bit(0, C)
+                        op_storb(dst, res)
+                        C = src bit 7
+                        N = res bit 7
+                        Z = res == 0.toUByte()
+                        V = N xor C
+                    } // ROLB
+                    2 -> { // ASRB
+                        val dst = opc_dstb(opcode)
+                        val src = op_loadb(dst).toByte()
+                        val res = (src shr 1).toUByte()
+                        op_storb(dst, res)
+                        N = res bit 7
+                        Z = res == 0.toUByte()
+                        C = src bit 0
+                        V = N xor C
+                    } // ASRB
+                    3 -> { // ASLB
+                        val dst = opc_dstb(opcode)
+                        val src = op_loadb(dst)
+                        val res = (src shl 1).toUByte()
+                        op_storw(dst, res.toUShort())
+                        N = res bit 7
+                        Z = res == 0.toUByte()
+                        C = src bit 7
+                        V = N xor C
+                    } // ASLB
+                }
+                0x8D00 -> when (opcode shr 6 and 3) {
+                    1 -> { throw InvalidOpcodeException() } // MFPD // TODO
+                    2 -> { throw InvalidOpcodeException() } // MTPD // TODO
+                    else -> { throw InvalidOpcodeException() } // Reserved
+                }
             }
+            0x1000 -> { // MOV
+                val src = opc_src(opcode)
+                val dst = opc_dst(opcode)
+                op_loadw(src).also {
+                    op_storw(dst, it)
+                    N = it bit 15
+                    Z = it == 0.toUShort()
+                    V = false
+                }
+            } // MOV
+            0x2000 -> { // CMP
+                val src = op_loadw(opc_src(opcode))
+                val src2 = op_loadw(opc_dst(opcode))
+                val res = (src - src2) and 0xFFFFu
+                N = res bit 15
+                Z = res == 0U
+                C = src < src2 // unsigned lt
+                V = ((src bit 15) xor (src2 bit 15)) and ((src2 bit 15) == (res bit 15))
+            } // CMP
             0x3000 -> { // BIT
                 val src = opc_src(opcode)
                 val dst = opc_dst(opcode)
@@ -263,7 +578,36 @@ class CPU(private val core: AddressSpace) {
                 V = (src_sign == dstv and 0x8000u) && (src_sign != resw and 0x8000u)
                 C = (resw >= 0x10000u)
             } // ADD
-            7000 -> when (opcode shr 9 and 0x7) {
+            0x7000 -> when (opcode shr 9 and 0x7) {
+                0 -> { // MUL
+                    val r = opcode shr 6 and 0x7
+                    val src = op_loadw(opc_src(opcode)).toShort().toInt()
+                    val res = registers[r].toShort().toInt() * src
+                    registers[r bis 1] = (res shr 16).toUShort()
+                    registers[r] = res.toUShort()
+                    N = res bit 31
+                    Z = res == 0
+                    V = false
+                    C = (res shr 16) == -(res shr 15 and 1) // check if overflow extends the sign bit
+                } // MUL
+                1 -> { // DIV
+                    val r = opcode shr 6 and 0x7
+                    val src = op_loadw(opc_src(opcode)).toInt()
+                    val lho = (registers[r].toUInt() shl 16 or registers[r bis 1].toUInt()).toInt()
+                    if (src != 0) {
+                        val quot = lho / src
+                        val rem = lho % src
+                        registers[r] = quot.toUShort()
+                        registers[r bis 1] = rem.toUShort()
+                        val overflow = quot shr 16
+                        V = overflow == -(quot shr 15 and 1) // check if overflow extends the sign bit
+                        N = quot bit 15
+                        Z = quot == 0
+                    } else {
+                        C = true
+                        V = true
+                    }
+                } // DIV
                 2 -> { // ASH
                     val r = opcode shr 6 and 0x7
                     var count = (op_loadb(opc_src(opcode)) and 0x3Fu).toInt()
@@ -309,25 +653,64 @@ class CPU(private val core: AddressSpace) {
                         C = false
                         src
                     }
-                    val resS = res.toUShort()
                     registers[r] = (res and 0xFFFF).toUShort()
                     registers[r or 1] = (res shr 16 and 0xFFFF).toUShort()
                     N = res < 0
                     Z = res == 0
                 } // ASHC
-
+                4 -> {
+                    val r = opcode shr 6 and 7
+                    val dst = opc_dst(r)
+                    val res = op_loadw(dst) xor registers[r]
+                    op_storw(dst, res)
+                    N = res bit 15
+                    Z = res == 0.toUShort()
+                    V = false
+                }
+                5,6 -> throw InvalidOpcodeException()
+                7 -> {
+                    val reg = opcode shr 6 and 7
+                    registers[reg] = registers[reg].dec()
+                    if (registers[reg] != 0.toUShort()) {
+                        pc = (pc.toInt() - (opcode and 0x3F shl 1)).toUShort()
+                    }
+                } // SOB
             }
+            // 0x800 handled above
+            0x9000 -> { // MOVB
+                val src = opc_srcb(opcode)
+                val dst = opc_dstb(opcode)
+                op_loadb(src).also {
+                    if (dst bit 32) {
+                        op_storw(dst, it.toUShort() sex 8)
+                    } else {
+                        op_storb(dst, it)
+                    }
+                    N = it bit 15
+                    Z = it == 0.toUByte()
+                    V = false
+                }
+            } // MOVB
+            0xA000 -> { // CMPB
+                val src = op_loadb(opc_srcb(opcode))
+                val src2 = op_loadb(opc_dstb(opcode))
+                val res = (src - src2) and 0xFFu
+                N = res bit 8
+                Z = res == 0U
+                C = src < src2 // unsigned lt
+                V = ((src bit 8) xor (src2 bit 8)) and ((src2 bit 8) == (res bit 8))
+            } // CMPB
             0xB000 -> { // BITB
-                val src = opc_src(opcode)
-                val dst = opc_dst(opcode)
+                val src = opc_srcb(opcode)
+                val dst = opc_dstb(opcode)
                 val res = op_loadb(dst) and op_loadb(src).inv()
                 N = res bit 7
                 Z = res != 0u.toUByte()
                 V = false
             } // BITB
             0xC000 -> { // BICB
-                val src = opc_src(opcode)
-                val dst = opc_dst(opcode)
+                val src = opc_srcb(opcode)
+                val dst = opc_dstb(opcode)
                 val res = op_loadb(dst) and op_loadb(src).inv()
                 op_storb(dst, res)
                 N = res bit 7
@@ -335,15 +718,52 @@ class CPU(private val core: AddressSpace) {
                 V = false
             } // BICB
             0xD000 -> { // BISB
-                val src = opc_src(opcode)
-                val dst = opc_dst(opcode)
+                val src = opc_srcb(opcode)
+                val dst = opc_dstb(opcode)
                 val res = op_loadb(dst) or op_loadb(src)
                 op_storb(dst, res)
                 N = res bit 7
                 Z = res != 0u.toUByte()
                 V = false
             } // BISB
-
+            0xE000 -> {
+                val src = opc_src(opcode)
+                val dst = opc_dst(opcode)
+                val srcv = op_loadw(src)
+                val dstv = op_loadw(dst)
+                val res = (dstv.toShort() - srcv.toShort())
+                op_storw(dst, res.toUShort())
+                N = res < 0
+                Z = res == 0
+                V = ((srcv bit 31) xor (dstv bit 15)) and ((srcv bit 15) == (res bit 31))
+                C = (dst.toInt() + src.inv().inc().toInt()) < 0x1_0000
+            } // SUB
         }
     }
+
+    fun trap(vector: UShort) {
+        stack_push(psw)
+        stack_push(pc)
+        pc = core.getw(vector)
+        psw = core.getw((vector + 2u).toUShort())
+    }
+
+    private inner class Registers: PAddressSpace {
+        override fun getw(addr: UInt): UShort = when (addr) {
+            0x3FFFEu -> psw
+            else -> throw MemoryError(MemoryErrorType.BusTimeout, addr)
+        }
+
+        override fun setw(addr: UInt, value: UShort) = when (addr) {
+            0x3FFFEu -> psw = value
+            else -> throw MemoryError(MemoryErrorType.BusTimeout, addr)
+        }
+    }
+
+    enum class RunState(val handleInterrupt: Boolean) {
+        RUNNING(handleInterrupt = true),
+        HALTED(handleInterrupt = false),
+        WAIT_FOR_INTERRUPT(handleInterrupt = true)
+    }
+
 }
diff --git a/src/main/kotlin/com/thequux/mcpdp/core/HaltInsn.kt b/src/main/kotlin/com/thequux/mcpdp/core/HaltInsn.kt
new file mode 100644
index 0000000..88dd450
--- /dev/null
+++ b/src/main/kotlin/com/thequux/mcpdp/core/HaltInsn.kt
@@ -0,0 +1,5 @@
+package com.thequux.mcpdp.core
+
+class HaltInsn : Throwable() {
+
+}
diff --git a/src/main/kotlin/com/thequux/mcpdp/core/MemoryError.kt b/src/main/kotlin/com/thequux/mcpdp/core/MemoryError.kt
new file mode 100644
index 0000000..cd01292
--- /dev/null
+++ b/src/main/kotlin/com/thequux/mcpdp/core/MemoryError.kt
@@ -0,0 +1,9 @@
+package com.thequux.mcpdp.core
+
+class MemoryError(val type: MemoryErrorType, var addr: UInt): Exception("Memory error $type at ${addr.toString(8)}")
+
+enum class MemoryErrorType {
+    BusTimeout,
+    OddAddress,
+    NonExistent,
+}
diff --git a/src/main/kotlin/com/thequux/mcpdp/core/PagingUnit.kt b/src/main/kotlin/com/thequux/mcpdp/core/PagingUnit.kt
new file mode 100644
index 0000000..cd2e7fe
--- /dev/null
+++ b/src/main/kotlin/com/thequux/mcpdp/core/PagingUnit.kt
@@ -0,0 +1,206 @@
+
+package com.thequux.mcpdp.core
+
+import com.thequux.mcpdp.ext.bit.bic
+import com.thequux.mcpdp.ext.bit.bit
+import com.thequux.mcpdp.ext.bit.shr
+import com.thequux.mcpdp.peripheral.Unibus
+import com.thequux.mcpdp.util.ProgrammerError
+
+enum class AccessAction {
+    Allow,
+    Trap,
+    Abort,
+}
+enum class ACF(val bin: UShort, val read: AccessAction, val write: AccessAction) {
+    NonResident(0U, AccessAction.Abort, AccessAction.Abort),
+    ReadTrap(1U, AccessAction.Trap, AccessAction.Abort),
+    ReadOnly(2U, AccessAction.Abort, AccessAction.Allow),
+    Unused1(3U, AccessAction.Abort, AccessAction.Abort),
+    TrapAlways(4U, AccessAction.Trap, AccessAction.Trap),
+    WriteTrap(5U, AccessAction.Allow, AccessAction.Trap),
+    ReadWrite(6U, AccessAction.Allow, AccessAction.Allow),
+    Unused2(7U, AccessAction.Abort, AccessAction.Abort);
+
+    fun action(writep: Boolean): AccessAction = if (writep) write else read
+    companion object {
+        fun fromField(value: UShort): ACF = when ((value and 0x7U).toInt()) {
+            0 -> NonResident
+            1 -> ReadTrap
+            2 -> ReadOnly
+            3 -> Unused1
+            4 -> TrapAlways
+            5 -> WriteTrap
+            6 -> ReadWrite
+            7 -> Unused2
+            else -> throw ProgrammerError("Unreachable")
+        }
+    }
+}
+private data class PDR(val plf: UShort, var A: Boolean, var W: Boolean, var ed: Boolean, var acf: ACF) {
+    constructor(): this(0U, false, false, false, ACF.NonResident)
+    constructor(value: UShort): this(value shr 8 and 0x7Fu, false, false, value bit 3, ACF.fromField(value))
+
+    val range: UIntRange
+        get() = if (ed) {
+            (0x2000U - (plf.toUInt() shl 6))..0x1FFFu
+        } else {
+            0U..((plf.toUInt() shl 6) -1U)
+        }
+    fun touched() { A = true }
+    fun written() { A = true; W = true }
+}
+
+@OptIn(ExperimentalUnsignedTypes::class)
+class PagingUnit(val pspace: PAddressSpace): VAddressSpace {
+
+    private var mmr = UShortArray(4)
+    private var enableUnibusMap: Boolean = false
+    private var enable22bit: Boolean = false
+    private var enableDSpaceByMode = BooleanArray(4)
+
+    /// The 18-bit address space exposed to peripherals
+    val unibusMap: PAddressSpace = UnibusMap()
+
+    private inner class PageTable(val mode: Int, val dspace: Boolean) {
+        val par = UShortArray(16) { 0U }
+        val pdr = Array(16) { PDR() }
+
+
+        fun setMmr0(causeBit: Int, apf: Int, completed: Boolean = false) {
+            val reg = mmr[0].toInt()
+            val cause_flag = 1 shl causeBit
+            if (reg and 0xF000 and -cause_flag == 0) {
+                // no higher priority flags
+                mmr[0] = (reg and 0xF200
+                        or 0x4000 // trap: page length
+                        or mode.shl(5)
+                        or (if (completed) 0x80 else 0)
+                        or (if (dspace) 8 else 0)
+                        or apf).toUShort()
+            }
+        }
+        fun map(addr: UShort, write: Boolean): UInt {
+            val apf = (addr shr 13).toInt()
+            val par = par[apf]
+            val pdr = pdr[apf]
+            if (write) pdr.written() else pdr.touched()
+            var trap = false
+            // check range
+            if (addr and 0x1FFFU !in pdr.range) {
+                setMmr0(14, apf)
+                // TODO: handle rest of trap
+                throw Trap(0xA8)
+            }
+            when (pdr.acf.action(write)) {
+                AccessAction.Allow -> {}
+                AccessAction.Trap -> {
+                    setMmr0(12, apf, true)
+                    trap = true
+                }
+                AccessAction.Abort -> {
+                    setMmr0(13, apf)
+                    throw Trap(0xA8)
+                }
+            }
+            return addr.toUInt() + (par.toUInt() shl 6) and 0x3F_FFFFu
+        }
+    }
+
+    var mode: Int = 0
+
+    private val itabs: Array<PageTable> = Array(3) { PageTable(if (it == 2) 3 else it, dspace = false) }
+    private val dtabs: Array<PageTable> = Array(3) { PageTable(if (it == 2) 3 else it, dspace = true) }
+    private var curIspace: PageTable = itabs[0]
+    private var curDspace: PageTable = dtabs[0]
+    private val unibusTable = UIntArray(32)
+
+    private fun getSpace(dspace: Boolean): PageTable = if (dspace) curDspace else curIspace
+    override fun getw(addr: UShort, dspace: Boolean): UShort = pspace.getw(getSpace(dspace).map(addr, write = false))
+
+    override fun getb(addr: UShort): UByte = pspace.getb(curDspace.map(addr, write = false))
+
+    override fun setw(addr: UShort, value: UShort, dspace: Boolean) {
+        pspace.setw(getSpace(dspace).map(addr, write = true), value)
+    }
+
+    override fun setb(addr: UShort, value: UByte) {
+        pspace.setb(curDspace.map(addr, write = true), value)
+    }
+
+    companion object {
+        private val MMR3: UInt = 0x3F54Eu
+    }
+    private inner class ConfigRegisters: PAddressSpace {
+
+        override fun getw(addr: UInt): UShort = when (addr) {
+            MMR3 -> {
+                (0U.bit(0, enableDSpaceByMode[3])
+                    .bit(1, enableDSpaceByMode[1])
+                    .bit(2, enableDSpaceByMode[0])
+                    .bit(4, enable22bit)
+                    .bit(5, enableUnibusMap)
+                    .toUShort())
+            } // 772516 MMR3
+            else -> throw MemoryError(MemoryErrorType.BusTimeout, addr)
+        }
+
+        override fun setw(addr: UInt, value: UShort): Unit = when(addr) {
+            MMR3 -> {
+                enableUnibusMap = value bit 5
+                enable22bit = value bit 4
+                enableDSpaceByMode[0] = value bit 2
+                enableDSpaceByMode[1] = value bit 1
+                enableDSpaceByMode[3] = value bit 0
+            }
+            in 0x3F080u..0x3F0FFu -> {
+                val uaddr = (addr shr 1 and 31u).toInt()
+                val hiWord = addr bit 1
+                if (hiWord) {
+                    unibusTable[uaddr] = unibusTable[uaddr] and 0xFFFFu or (value.toUInt() and 0x3Fu shl 16)
+                } else {
+                    unibusTable[uaddr] = unibusTable[uaddr] and 0xFFFF_0000u or (value.toUInt() bic 0)
+                }
+            } // 770200..770377 Unibus map
+            else -> throw MemoryError(MemoryErrorType.BusTimeout, addr)
+        }
+
+    }
+
+    fun mount(unibus: Unibus) {
+        val regs = ConfigRegisters()
+        unibus.run {
+            deviceView = UnibusMap()
+            attach(0x3_FF80u, 6, regs) // User PAR/PDR
+            attach(0x3_FF7Au, 1, regs) // MMR0
+            attach(0x3_FF7Cu, 2, regs) // MMR1-2
+            attach(0x3_F54Eu, 1, regs) // MMR3
+            attach(0x3_F4C0u, 6, regs) // Kernal PAR/PDF
+            attach(0x3_F480u, 6, regs) // Supervisor PAR/PDR
+            attach(0x3_F080u, 7, regs) // Unibus map
+
+        }
+
+    }
+    private inner class UnibusMap: PAddressSpace {
+        // This implements an *18-bit* address space, for the view of unibus peripherals
+
+        private fun map(addr: UInt): UInt {
+            val uaddr = addr and 0x3_FFFFu
+            return if (uaddr > 0x3_0000u) {
+                // I/O page is always mapped as follows
+                addr or 0x3FC000u
+            } else {
+                unibusTable[(uaddr shr 13).toInt()] + (uaddr and 0x1FFFu) or 0x3C0000U
+            }
+        }
+
+        override fun getw(addr: UInt): UShort = pspace.getw(map(addr))
+        override fun getb(addr: UInt): UByte = pspace.getb(map(addr))
+
+        override fun setw(addr: UInt, value: UShort) = pspace.setw(map(addr), value)
+        override fun setb(addr: UInt, value: UByte) = pspace.setb(map(addr), value)
+
+
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/com/thequux/mcpdp/peripheral/MemBus.kt b/src/main/kotlin/com/thequux/mcpdp/peripheral/MemBus.kt
new file mode 100644
index 0000000..ae380ad
--- /dev/null
+++ b/src/main/kotlin/com/thequux/mcpdp/peripheral/MemBus.kt
@@ -0,0 +1,58 @@
+package com.thequux.mcpdp.peripheral
+
+import com.thequux.mcpdp.core.MemoryError
+import com.thequux.mcpdp.core.MemoryErrorType
+import com.thequux.mcpdp.core.PAddressSpace
+import com.thequux.mcpdp.ext.bit.bit
+import com.thequux.mcpdp.util.ConfigurationError
+
+/// This is the main dispatcher for the PDP-11 address space, as seen from the PDP-11 CPU
+///
+/// Size represents the amount of physical memory, and must be a multiple of 32
+@OptIn(ExperimentalUnsignedTypes::class)
+class MemBus(val size: Int) : PAddressSpace {
+    private val data: UShortArray
+    public val unibus = Unibus()
+
+    init {
+        if (size % 64 != 0) {
+            throw ConfigurationError("Memory size must be a multiple of 64 bytes")
+        }
+        if (size < 0) {
+            throw ConfigurationError("Memory size must be positive")
+        }
+        if (size > 0x3C_0000) {
+            throw ConfigurationError("Memory overlaps unibus")
+        }
+        data = UShortArray(size shr 1)
+        unibus.attach(0x3FFF0u, 2, Registers())
+    }
+
+    private inner class Registers: PAddressSpace {
+        override fun getw(addr: UInt): UShort = when (addr) {
+            0x3FFF2u -> 0u // upper size
+            0x3FFF0u -> (size shr 6).toUShort()
+            else -> throw MemoryError(MemoryErrorType.BusTimeout, addr)
+        }
+
+        // Both registers are write-only
+        override fun setw(addr: UInt, value: UShort) {}
+    }
+
+    override fun getw(addr: UInt): UShort {
+        if (size bit 0) {
+            throw MemoryError(MemoryErrorType.OddAddress, addr)
+        }
+        return when (addr.toInt()) {
+            in 0..size.dec() -> data[addr.toInt() shr 1]
+            in 0x3c0000..0x3FFFFF -> unibus.getw(addr)
+            else -> throw MemoryError(MemoryErrorType.NonExistent, addr)
+        }
+    }
+
+    override fun setw(addr: UInt, value: UShort) {
+        if (size bit 0) {
+            throw MemoryError(MemoryErrorType.OddAddress, addr)
+        }
+    }
+}
diff --git a/src/main/kotlin/com/thequux/mcpdp/peripheral/Unibus.kt b/src/main/kotlin/com/thequux/mcpdp/peripheral/Unibus.kt
new file mode 100644
index 0000000..ff53ed8
--- /dev/null
+++ b/src/main/kotlin/com/thequux/mcpdp/peripheral/Unibus.kt
@@ -0,0 +1,71 @@
+package com.thequux.mcpdp.peripheral
+
+import com.thequux.mcpdp.core.MemoryError
+import com.thequux.mcpdp.core.MemoryErrorType
+import com.thequux.mcpdp.core.PAddressSpace
+import com.thequux.mcpdp.util.ConfigurationError
+import com.thequux.mcpdp.util.ProgrammerError
+import java.lang.Integer.min
+
+interface Region {
+    fun attach(address: UInt, suffix: Int, device: PAddressSpace)
+
+    fun map(address: UInt): PAddressSpace?
+}
+
+private class MappedDevice(val device: PAddressSpace): Region {
+    override fun attach(address: UInt, suffix: Int, device: PAddressSpace) {
+        throw ConfigurationError("Attempted to map one device over another at ${address.toString(8)}")
+    }
+
+    override fun map(address: UInt): PAddressSpace = device
+}
+
+/// Note: this is open and public as an implementation detail.
+open class Subregion(private val suffix: Int, private val size: Int): Region {
+    val map: Array<Region?>
+    val mask: UInt = (1u shl size).dec()
+    val submask = (1u shl suffix).dec()
+    init {
+        if (suffix + size > 18) {
+            throw ProgrammerError("tried to construct a mapper for more address space than exists")
+        }
+        map = Array(1 shl size) { null }
+    }
+
+    override fun attach(address: UInt,  suffix: Int, device: PAddressSpace) {
+        val loc = (address shr suffix and mask).toInt()
+        if (suffix <= 0) throw ProgrammerError("Suffix must be positive")
+        if (suffix < this.suffix) {
+            // needs a submap
+            if (map[loc] == null) {
+                // Divisions at /12, /6, and /3
+                val subsize = if (this.suffix == 6) 3 else min(size, this.suffix)
+                map[loc] = Subregion(this.suffix - subsize, subsize)
+            }
+            map[loc]!!.attach(address, suffix, device)
+        } else {
+            val nunits = 1 shl (suffix - this.suffix)
+            for (i in 0..nunits.dec()) {
+               if (map[loc + i] != null) {
+                   throw ConfigurationError("Unibus conflict at ${(address and submask.inv()).toString(8)}/${18-suffix}")
+               }
+                map[loc+i] = MappedDevice(device)
+            }
+        }
+    }
+
+    override fun map(address: UInt): PAddressSpace? = map[(address shr suffix and mask).toInt()]?.map(address)
+}
+
+class Unibus: PAddressSpace, Subregion(12, 6) {
+    /// The view of the unibus from a device
+    var deviceView: PAddressSpace = this
+        internal set
+    override fun map(address: UInt): PAddressSpace =
+        super.map(address) ?: throw MemoryError(MemoryErrorType.BusTimeout, address)
+    override fun getw(addr: UInt): UShort = map(addr).getw(addr)
+    override fun getb(addr: UInt): UByte = map(addr).getb(addr)
+    override fun setw(addr: UInt, value: UShort) = map(addr).setw(addr, value)
+    override fun setb(addr: UInt, value: UByte) = map(addr).setb(addr, value)
+}
diff --git a/src/main/kotlin/com/thequux/mcpdp/util/ConfigurationError.kt b/src/main/kotlin/com/thequux/mcpdp/util/ConfigurationError.kt
new file mode 100644
index 0000000..6ca88fb
--- /dev/null
+++ b/src/main/kotlin/com/thequux/mcpdp/util/ConfigurationError.kt
@@ -0,0 +1,4 @@
+package com.thequux.mcpdp.util
+
+class ConfigurationError(message: String?) : Exception(message) {
+}
\ No newline at end of file
diff --git a/src/main/kotlin/com/thequux/mcpdp/util/ProgrammerError.kt b/src/main/kotlin/com/thequux/mcpdp/util/ProgrammerError.kt
new file mode 100644
index 0000000..9c71271
--- /dev/null
+++ b/src/main/kotlin/com/thequux/mcpdp/util/ProgrammerError.kt
@@ -0,0 +1,4 @@
+package com.thequux.mcpdp.util
+
+class ProgrammerError(message: String?) : Error(message) {
+}
\ No newline at end of file