Initial commit

2022-02-18 21:02:17 -06:00
commit 699477c651
11 changed files with 871 additions and 0 deletions
@@ -0,0 +1 @@
+/target
@@ -0,0 +1,8 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml
+# Editor-based HTTP Client requests
+/httpRequests/
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/.idea/vulcan-emu.iml" filepath="$PROJECT_DIR$/.idea/vulcan-emu.iml" />
+    </modules>
+  </component>
+</project>
@@ -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>
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="CPP_MODULE" version="4">
+  <component name="NewModuleRootManager">
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+      <excludeFolder url="file://$MODULE_DIR$/target" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>
@@ -0,0 +1,85 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
+[[package]]
+name = "getrandom"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "418d37c8b1d42553c93648be529cb70f920d3baf8ef469b74b9638df426e0b4c"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "wasi",
+]
+
+[[package]]
+name = "libc"
+version = "0.2.117"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e74d72e0f9b65b5b4ca49a346af3976df0f9c61d550727f349ecd559f251a26c"
+
+[[package]]
+name = "ppv-lite86"
+version = "0.2.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
+[[package]]
+name = "rand"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2e7573632e6454cf6b99d7aac4ccca54be06da05aca2ef7423d22d27d4d4bcd8"
+dependencies = [
+ "libc",
+ "rand_chacha",
+ "rand_core",
+ "rand_hc",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6c10a63a0fa32252be49d21e7709d4d4baf8d231c2dbce1eaa8141b9b127d88"
+dependencies = [
+ "ppv-lite86",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.6.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d34f1408f55294453790c48b2f1ebbb1c5b4b7563eb1f418bcfcfdbb06ebb4e7"
+dependencies = [
+ "getrandom",
+]
+
+[[package]]
+name = "rand_hc"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d51e9f596de227fda2ea6c84607f5558e196eeaf43c986b724ba4fb8fdf497e7"
+dependencies = [
+ "rand_core",
+]
+
+[[package]]
+name = "vulcan-emu"
+version = "0.1.0"
+dependencies = [
+ "rand",
+]
+
+[[package]]
+name = "wasi"
+version = "0.10.2+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fd6fbd9a79829dd1ad0cc20627bf1ed606756a7f77edff7b66b7064f9cb327c6"
@@ -0,0 +1,9 @@
+[package]
+name = "vulcan-emu"
+version = "0.1.0"
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+rand = "0.8.0"
@@ -0,0 +1,66 @@
+// 128k, the amount of memory in a standard Vulcan machine
+pub const MEM_SIZE: u32 = 128 * 1024;
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
+pub struct Address(u32);
+
+impl From<Address> for usize {
+    fn from(a: Address) -> Self { (a.0 & (MEM_SIZE-1)) as usize }
+}
+
+impl From<u32> for Address {
+    fn from(a: u32) -> Self { Self(a & 0xffffff) }
+}
+
+impl Into<u32> for Address {
+    fn into(self) -> u32 { self.0 }
+}
+
+impl std::ops::Add<i32> for Address {
+    type Output = Address;
+    fn add(self, rhs: i32) -> Self::Output {
+        Address::from((self.0 as i32).overflowing_add(rhs).0 as u32)
+    }
+}
+
+impl std::ops::Sub<i32> for Address {
+    type Output = Address;
+    fn sub(self, rhs: i32) -> Self::Output { self + -rhs }
+}
+
+impl std::ops::SubAssign<i32> for Address {
+    fn sub_assign(&mut self, rhs: i32) { *self = *self - rhs; }
+}
+
+impl std::ops::AddAssign<i32> for Address {
+    fn add_assign(&mut self, rhs: i32) { *self = *self + rhs; }
+}
+
+#[test]
+fn test_address_truncation() {
+    let a: Address = 0x11223344.into();
+    assert_eq!(a, 0x00223344.into());
+}
+
+#[test]
+fn test_addressing_arrays() {
+    let a: usize = Address::from(0xffffff).into();
+    assert_eq!(a, 0x01ffff as usize);
+}
+
+#[test]
+fn test_address_overflows() {
+    let a = Address::from(0xfffffa);
+    assert_eq!(a + 10, Address(4));
+
+    let b = Address::from(3);
+    assert_eq!(b - 10, Address(0xfffff9));
+
+    let mut c = Address::from(5);
+    c += 3;
+    assert_eq!(c, Address(8));
+
+    let mut d = Address::from(5);
+    d -= 3;
+    assert_eq!(d, Address(2));
+}
@@ -0,0 +1,487 @@
+mod memory;
+mod address;
+mod opcodes;
+
+use memory::Memory;
+use memory::PeekPoke;
+use address::Address;
+use opcodes::Opcode;
+use crate::opcodes::InvalidOpcode;
+use std::convert::TryFrom;
+
+struct CPU {
+    memory: Memory, // Main memory, all of it
+    pc: Address, // program counter, address of the low byte of the instruction
+    dp: Address, // data pointer, address of the low byte of one cell above the data stack
+    sp: Address, // stack pointer, address of the low byte of the return stack
+    iv: Address, // interrupt vector
+    int_enabled: bool, // interrupt enable bit
+    halted: bool, // Whether the CPU is halted
+}
+
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+struct Instruction {
+    opcode: Opcode,
+    arg: Option<u32>,
+    length: u8
+}
+
+impl CPU {
+    fn new(memory: Memory) -> Self {
+        Self {
+            memory,
+            pc: 1024.into(),
+            dp: 256.into(),
+            sp: 1024.into(),
+            iv: 1024.into(),
+            int_enabled: false,
+            halted: true,
+        }
+    }
+
+    fn reset(&mut self) {
+        self.pc = 1024.into();
+        self.dp = 256.into();
+        self.sp = 1024.into();
+        self.iv = 1024.into();
+        self.int_enabled = false;
+        self.halted = true;
+    }
+
+    fn push_data<A: Into<u32>>(&mut self, word: A) {
+        self.memory.poke24(self.dp, word.into());
+        self.dp += 3;
+    }
+
+    fn push_call<A: Into<u32>>(&mut self, word: A) {
+        self.sp -= 3;
+        self.memory.poke24(self.sp, word.into());
+    }
+
+    fn pop_data(&mut self) -> u32 {
+        self.dp -= 3;
+        self.memory.peek24(self.dp)
+    }
+
+    fn pop_call(&mut self) -> u32 {
+        let val = self.memory.peek24(self.sp);
+        self.sp += 3;
+        val
+    }
+
+    fn peek_call(&self) -> u32 {
+        self.memory.peek24(self.sp)
+    }
+
+    fn peek_data(&self) -> u32 {
+        self.memory.peek24(self.dp - 3)
+    }
+
+    fn fetch(&self) -> Result<Instruction, InvalidOpcode> {
+        let instruction = self.memory.peek(self.pc);
+        match Opcode::try_from(instruction >> 2) {
+            Ok(opcode) => {
+                let arg_length = instruction & 3;
+                if arg_length == 0 {
+                    Ok(Instruction {
+                        opcode: opcode,
+                        arg: None,
+                        length: 1
+                    })
+                } else {
+                    let mut arg = 0u32;
+                    for n in 0..arg_length {
+                        let mut b: u32 = self.memory.peek(self.pc + (n + 1) as i32) as u32;
+                        b = b << (8 * n);
+                        arg += b;
+                    }
+                    Ok(Instruction {
+                        opcode: opcode,
+                        arg: Some(arg),
+                        length: arg_length + 1
+                    })
+                }
+            },
+            Err(e) => Err(e)
+        }
+    }
+
+    fn execute(&mut self, instruction: Instruction) -> Address {
+        if let Some(arg) = instruction.arg {
+            self.push_data(arg)
+        }
+
+        if instruction.opcode.is_binary() {
+            let x = self.pop_data();
+            let y = self.pop_data();
+
+            match instruction.opcode {
+                Opcode::Add => { self.push_data(x + y) }
+                Opcode::Sub => { self.push_data(y - x) }
+                Opcode::Mul => { self.push_data(y * x) }
+                Opcode::Div => { self.push_data(y / x) }
+                Opcode::Mod => { self.push_data(y % x) }
+                Opcode::And => { self.push_data(y & x) }
+                Opcode::Or => { self.push_data(y | x) }
+                Opcode::Xor => { self.push_data(y ^ x) }
+                Opcode::Gt => { self.push_data(bool_as_word(y > x)) }
+                Opcode::Lt => { self.push_data(bool_as_word(y < x)) }
+                Opcode::Agt => { self.push_data(bool_as_word(word_as_signed(y) > word_as_signed(x))) }
+                Opcode::Alt => { self.push_data(bool_as_word(word_as_signed(y) < word_as_signed(x))) }
+                Opcode::Lshift => { self.push_data(y << x) }
+                Opcode::Rshift => { self.push_data(y >> x) }
+                Opcode::Arshift => {
+                    if y & 0x800000 != 0 {
+                        let mut shifted = y;
+                        for _ in 0..x {
+                            shifted = shifted >> 1 | 0x800000;
+                        }
+                        self.push_data(shifted)
+                    } else {
+                        self.push_data(y >> x)
+                    }
+                }
+                Opcode::Swap => {
+                    self.push_data(x);
+                    self.push_data(y)
+                }
+                Opcode::Store => { self.memory.poke(x, y as u8) }
+                Opcode::Storew => { self.memory.poke24(x, y) }
+                Opcode::Setsdp => {
+                    self.dp = x.into();
+                    self.sp = y.into()
+                }
+                Opcode::Brz => { if y == 0 { return self.pc + word_as_signed(x) } }
+                Opcode::Brnz => { if y != 0 { return self.pc + word_as_signed(x) } }
+                _ => {} // This can never happen
+            }
+            self.pc + instruction.length as i32
+        } else {
+            match instruction.opcode {
+                Opcode::Nop => { /* No action required */ }
+                Opcode::Rand => {} // TODO remove this whole instruction
+                Opcode::Not => {
+                    let x = self.pop_data();
+                    self.push_data(bool_as_word(x == 0))
+                }
+                Opcode::Pop => { self.pop_data(); }
+                Opcode::Dup => { self.push_data(self.peek_data()) }
+                Opcode::Pick => {
+                    let index = self.pop_data();
+                    let val = self.memory.peek24(self.dp - (index as i32 + 1) * 3);
+                    self.push_data(val)
+                }
+                Opcode::Rot => {
+                    let x = self.pop_data();
+                    let y = self.pop_data();
+                    let z = self.pop_data();
+                    self.push_data(y);
+                    self.push_data(x);
+                    self.push_data(z)
+                }
+                Opcode::Jmp => { return self.pop_data().into() }
+                Opcode::Jmpr => {
+                    let x = word_as_signed(self.pop_data());
+                    return self.pc + x
+                }
+                Opcode::Call => {
+                    let x = self.pop_data();
+                    self.push_call(self.pc + instruction.length as i32);
+                    return x.into()
+                }
+                Opcode::Ret => { return self.pop_call().into() }
+                Opcode::Hlt => { self.halted = true }
+                Opcode::Load => {
+                    let x = self.pop_data();
+                    self.push_data(self.memory.peek(x) as u32)
+                }
+                Opcode::Loadw => {
+                    let x = self.pop_data();
+                    self.push_data(self.memory.peek24(x))
+                }
+                Opcode::Inton => { self.int_enabled = true }
+                Opcode::Intoff => { self.int_enabled = false }
+                Opcode::Setiv => { self.iv = self.pop_data().into() }
+                Opcode::Sdp => {
+                    self.push_data(self.sp);
+                    self.push_data(self.dp + 3) // The +3 accounts for the word we're about to push
+                }
+                Opcode::Pushr => {
+                    let x = self.pop_data();
+                    self.push_call(x)
+                }
+                Opcode::Popr => {
+                    let r = self.pop_call();
+                    self.push_data(r)
+                }
+                Opcode::Peekr => {
+                    let r = self.peek_call();
+                    self.push_data(r)
+                }
+                Opcode::Debug => { /* TODO This should print the stack or something */ }
+                _ => {} // This can never happen
+            }
+            self.pc + instruction.length as i32
+        }
+    }
+}
+
+impl Opcode {
+    fn is_binary(self) -> bool {
+        use Opcode::*;
+        self != Nop && self != Not && self != Rand && self != Pop && self != Dup && self != Pick &&
+            self != Rot && self != Jmp && self != Jmpr && self != Call && self != Ret &&
+            self != Hlt && self != Load && self != Loadw && self != Inton && self != Intoff &&
+            self != Setiv && self != Sdp && self != Pushr && self != Popr && self != Peekr &&
+            self != Debug
+    }
+}
+
+fn word_as_signed(word: u32) -> i32 {
+    if word & 0x800000 != 0 {
+        -(((word ^ 0xffffff) + 1) as i32)
+    } else {
+        word as i32
+    }
+}
+
+fn bool_as_word(flag: bool) -> u32 { if flag { 1 } else { 0 } }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use Opcode::*;
+
+    impl CPU {
+        fn get_stack(&self) -> Vec<u32> {
+            let mut v = Vec::new();
+            let mut curr = Address::from(256);
+            while curr < self.dp {
+                v.push(self.memory.peek24(curr));
+                curr += 3
+            }
+            v
+        }
+
+        fn get_call(&self) -> Vec<u32> {
+            let mut v = Vec::new();
+            let mut curr = Address::from(1024);
+            while curr > self.sp {
+                curr -= 3;
+                v.push(self.memory.peek24(curr));
+            }
+            v
+        }
+    }
+
+    fn predicate_opcode_test<P, Q>(opcode: Opcode, given: P, pred: Q) where P: FnOnce(&mut CPU), Q: FnOnce(&CPU)
+    {
+        let mut cpu = CPU::new(Memory::default());
+        given(&mut cpu);
+        let new_pc = cpu.execute(Instruction{ opcode: opcode, arg: None, length: 1 });
+        cpu.pc = new_pc;
+        pred(&mut cpu)
+    }
+
+    fn simple_opcode_test(given: Vec<u32>, opcode: Opcode, expected: Vec<u32>) {
+        predicate_opcode_test(opcode, |cpu| {
+            for i in given.into_iter() { cpu.push_data(i) }
+        }, |cpu| {
+            assert_eq!(cpu.get_stack(), expected)
+        })
+    }
+
+    fn call_stack_opcode_test(given: Vec<u32>, given_r: Vec<u32>, opcode: Opcode, expected: Vec<u32>, expected_r: Vec<u32>, pc: Address) {
+        predicate_opcode_test(opcode, |cpu| {
+            for i in given.into_iter() { cpu.push_data(i) }
+            for i in given_r.into_iter() { cpu.push_call(i) }
+        }, |cpu| {
+            assert_eq!(cpu.get_stack(), expected);
+            assert_eq!(cpu.get_call(), expected_r);
+            assert_eq!(pc, cpu.pc)
+        })
+    }
+
+    fn control_flow_opcode_test<A>(given: Vec<u32>, opcode: Opcode, expected_pc: A) where A: Into<Address> {
+        predicate_opcode_test(opcode, |cpu| {
+            for i in given.into_iter() { cpu.push_data(i) }
+        }, |cpu| {
+            assert_eq!(cpu.pc, expected_pc.into())
+        })
+    }
+
+    fn memory_opcode_test(given: Vec<u32>, given_memory: Vec<u8>, opcode: Opcode, expected: Vec<u32>, expected_memory: Option<Vec<u8>>) {
+        predicate_opcode_test(opcode,
+        |cpu| {
+            for i in given.into_iter() { cpu.push_data(i) }
+            for (offset, byte) in given_memory.into_iter().enumerate() {
+                cpu.memory.poke(Address::from(2048 + offset as u32), byte)
+            }
+        },
+        |cpu| {
+            if let Some(expected_memory) = expected_memory {
+                for (offset, byte) in expected_memory.into_iter().enumerate() {
+                    let actual = cpu.memory.peek(Address::from(2048 + offset as u32));
+                    assert_eq!(byte, actual, "At address 2048 + {}", offset)
+                }
+                assert_eq!(cpu.get_stack(), expected)
+            }
+        })
+    }
+
+    fn to_word(val: i32) -> u32 {
+        if val >= 0 {
+            val as u32
+        } else {
+            ((-val ^ 0xffffff) + 1) as u32
+        }
+    }
+
+    #[test]
+    fn test_arithmetic() {
+        simple_opcode_test(vec![5, 3], Add, vec![8]);
+        simple_opcode_test(vec![5, 3], Sub, vec![2]);
+        simple_opcode_test(vec![5, 3], Mul, vec![15]);
+        simple_opcode_test(vec![8, 3], Div, vec![2]);
+        simple_opcode_test(vec![10, 3], Mod, vec![1]);
+    }
+
+    #[test]
+    fn test_stack_manipulation() {
+        simple_opcode_test(vec![5], Dup, vec![5, 5]);
+        simple_opcode_test(vec![5, 3], Swap, vec![3, 5]);
+        simple_opcode_test(vec![10, 20, 30, 2], Pick, vec![10, 20, 30, 10]);
+        simple_opcode_test(vec![1, 4, 9], Rot, vec![4, 9, 1]);
+        simple_opcode_test(vec![1, 4, 9], Pop, vec![1, 4]);
+    }
+
+    #[test]
+    fn test_basic_ops() {
+        control_flow_opcode_test(vec![], Nop, 1025);
+        simple_opcode_test(vec![2], Nop, vec![2]);
+        predicate_opcode_test(Hlt, |_| { }, |cpu| { assert!(cpu.halted) })
+    }
+
+    #[test]
+    fn test_branching_jumping() {
+        control_flow_opcode_test(vec![1234], Jmp, 1234);
+        control_flow_opcode_test(vec![35], Jmpr, 1024 + 35);
+        control_flow_opcode_test(vec![to_word(-3)], Jmpr, 1024 - 3);
+        control_flow_opcode_test(vec![0, 35], Brnz, 1024 + 1);
+        control_flow_opcode_test(vec![17, 35], Brnz, 1024 + 35);
+        control_flow_opcode_test(vec![5, 35], Brz, 1024 + 1);
+        control_flow_opcode_test(vec![0, 35], Brz, 1024 + 35);
+    }
+
+    #[test]
+    fn test_memory() {
+        memory_opcode_test(vec![2048], vec![123], Load, vec![123], None);
+        memory_opcode_test(vec![2048], vec![0x12, 0x34, 0x56], Loadw, vec![0x123456], None);
+        memory_opcode_test(vec![100, 2048], vec![0x12, 0x34, 0x56], Store, vec![], Some(vec![100, 0x34, 0x56]));
+        memory_opcode_test(vec![0x112233, 2048], vec![0x12, 0x34, 0x56], Storew, vec![], Some(vec![0x33, 0x22, 0x11]));
+    }
+
+    #[test]
+    fn test_logic() {
+        simple_opcode_test(vec![0b111100, 0b001111], And, vec![0b001100]);
+        simple_opcode_test(vec![0b100, 0b001], Or, vec![0b101]);
+        simple_opcode_test(vec![0b101, 0b011], Xor, vec![0b110]);
+        simple_opcode_test(vec![5], Not, vec![0]);
+        simple_opcode_test(vec![0], Not, vec![1]);
+        simple_opcode_test(vec![5, 3], Gt, vec![1]);
+        simple_opcode_test(vec![5, 7], Gt, vec![0]);
+        simple_opcode_test(vec![5, 3], Lt, vec![0]);
+        simple_opcode_test(vec![5, 7], Lt, vec![1]);
+        simple_opcode_test(vec![5, to_word(-3)], Agt, vec![1]);
+        simple_opcode_test(vec![5, 10], Agt, vec![0]);
+        simple_opcode_test(vec![5, to_word(-3)], Alt, vec![0]);
+        simple_opcode_test(vec![5, 10], Alt, vec![1]);
+        simple_opcode_test(vec![0b1100, 2], Rshift, vec![3]);
+        simple_opcode_test(vec![0b1100, 2], Lshift, vec![0b110000]);
+        simple_opcode_test(vec![0x800010, 2], Arshift, vec![0xe00004]);
+    }
+
+    #[test]
+    fn test_cpu_call_stack() {
+        call_stack_opcode_test(vec![5000], vec![], Call, vec![], vec![1025], 5000.into());
+        call_stack_opcode_test(vec![], vec![5000], Ret, vec![], vec![], 5000.into());
+        call_stack_opcode_test(vec![], vec![], Sdp, vec![1024, 256 + 6], vec![], 1025.into());
+        predicate_opcode_test(Setsdp,
+        |cpu| {
+            cpu.push_data(1000u32);
+            cpu.push_data(2000u32)
+        },
+        |cpu| {
+            assert_eq!(cpu.sp, 1000.into());
+            assert_eq!(cpu.dp, 2000.into())
+        });
+        call_stack_opcode_test(vec![123], vec![], Pushr, vec![], vec![123], 1025.into());
+        call_stack_opcode_test(vec![], vec![123], Popr, vec![123], vec![], 1025.into());
+        call_stack_opcode_test(vec![], vec![123], Peekr, vec![123], vec![123], 1025.into());
+    }
+
+    #[test]
+    fn test_cpu_new() {
+        let cpu = CPU::new(Memory::default());
+        assert_eq!(cpu.pc, 1024.into());
+        assert_eq!(cpu.halted, true);
+    }
+
+    #[test]
+    fn test_cpu_reset() {
+        let mut cpu = CPU::new(Memory::default());
+        cpu.iv = 12345.into();
+        cpu.reset();
+        assert_eq!(cpu.iv, 1024.into());
+    }
+
+    #[test]
+    fn test_cpu_stacks() {
+        let mut cpu = CPU::new(Memory::default());
+        cpu.push_data(37u32);
+        cpu.push_data(45u32);
+        assert_eq!(cpu.memory.peek24(256), 37);
+        assert_eq!(cpu.memory.peek24(259), 45);
+
+        cpu.push_call(12u32);
+        cpu.push_call(34u32);
+        assert_eq!(cpu.memory.peek24(cpu.sp), 34);
+        assert_eq!(cpu.memory.peek24(cpu.sp + 3), 12);
+        assert_eq!(cpu.sp, (1024 - 6).into());
+        assert_eq!(cpu.dp, (256 + 6).into());
+
+        assert_eq!(cpu.pop_data(), 45);
+        assert_eq!(cpu.pop_data(), 37);
+        assert_eq!(cpu.dp, 256.into());
+
+        assert_eq!(cpu.pop_call(), 34);
+        assert_eq!(cpu.pop_call(), 12);
+        assert_eq!(cpu.sp, 1024.into());
+    }
+
+    #[test]
+    fn test_cpu_fetch() {
+        let mut cpu = CPU::new(Memory::default());
+        cpu.memory.poke(0x400, 0x01); // nop 1 arg
+        cpu.memory.poke(0x401, 0x02); // 2
+        cpu.memory.poke(0x402, 0x07); // add 3 arg
+        cpu.memory.poke24(0x403, 0x123456); // 3-byte arg
+        cpu.memory.poke(0x406, 29 << 2); // hlt
+        cpu.memory.poke(0x407, 0xfc); // gibberish
+
+        assert_eq!(cpu.fetch(), Ok(Instruction { opcode: Opcode::Nop, arg: Some(2), length: 2 }));
+
+        cpu.pc = 0x402.into();
+        assert_eq!(cpu.fetch(), Ok(Instruction { opcode: Opcode::Add, arg: Some(0x123456), length: 4 }));
+
+        cpu.pc = 0x406.into();
+        assert_eq!(cpu.fetch(), Ok(Instruction { opcode: Opcode::Hlt, arg: None, length: 1 }));
+
+        cpu.pc = 0x407.into();
+        assert_eq!(cpu.fetch(), Err(InvalidOpcode(0x3f)));
+    }
+}
+
+fn main() {
+    println!("Hello, world!");
+}
@@ -0,0 +1,70 @@
+use rand::Rng;
+use crate::address::Address;
+use crate::address::MEM_SIZE;
+
+pub struct Memory([u8; MEM_SIZE as usize]);
+
+impl Default for Memory {
+    fn default() -> Self { Self([0u8; MEM_SIZE as usize]) }
+}
+
+impl<R: Rng> From<R> for Memory {
+    fn from(mut rng: R) -> Self {
+        let mut mem = Memory::default();
+        for i in 0..(MEM_SIZE - 1) {
+            mem.0[i as usize] = rng.gen()
+        }
+        mem
+    }
+}
+
+impl std::ops::Index<Address> for Memory {
+    type Output = u8;
+    fn index(&self, index: Address) -> &Self::Output { &self.0[usize::from(index)] }
+}
+
+impl std::ops::IndexMut<Address> for Memory {
+    fn index_mut(&mut self, index: Address) -> &mut Self::Output { &mut self.0[usize::from(index)] }
+}
+
+pub trait PeekPoke {
+    fn peek<A: Into<Address>>(&self, addr: A) -> u8;
+    fn poke<A: Into<Address>>(&mut self, addr: A, val: u8);
+
+    fn peek24<A: Into<Address>>(&self, addr: A) -> u32 {
+        let addr = addr.into();
+        (self.peek(addr) as u32) | ((self.peek(addr + 1) as u32) << 8) | ((self.peek(addr + 2) as u32) << 16)
+    }
+
+    fn poke24<A: Into<Address>>(&mut self, addr: A, val: u32) {
+        let addr = addr.into();
+        self.poke(addr, val as u8);
+        self.poke(addr + 1, (val >> 8) as u8);
+        self.poke(addr + 2, (val >> 16) as u8);
+    }
+}
+
+impl PeekPoke for Memory {
+    fn peek<A: Into<Address>>(&self, addr: A) -> u8 { self[addr.into()] }
+    fn poke<A: Into<Address>>(&mut self, addr: A, val: u8) { self[addr.into()] = val; }
+}
+
+#[test]
+fn test_mem_peek_poke() {
+    let mut mem = Memory::default();
+    assert_eq!(mem.peek(35), 0);
+    mem.poke(35, 45);
+    assert_eq!(mem.peek(35), 45);
+    assert_eq!(mem.peek(36), 0);
+}
+
+#[test]
+fn test_mem_word_fns() {
+    let mut mem = Memory::default();
+    mem.poke24(10, 0x123456);
+    assert_eq!(mem.peek(10), 0x56);
+    assert_eq!(mem.peek(11), 0x34);
+    assert_eq!(mem.peek(12), 0x12);
+    assert_eq!(mem.peek24(10), 0x123456);
+    assert_eq!(mem.peek24(11), 0x001234);
+}
@@ -0,0 +1,120 @@
+use std::convert::TryFrom;
+use std::fmt::{Display, Formatter};
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum Opcode {
+    Nop,
+    Add,
+    Sub,
+    Mul,
+    Div,
+    Mod,
+    Rand,
+    And,
+    Or,
+    Xor,
+    Not,
+    Gt,
+    Lt,
+    Agt,
+    Alt,
+    Lshift,
+    Rshift,
+    Arshift,
+    Pop,
+    Dup,
+    Swap,
+    Pick,
+    Rot,
+    Jmp,
+    Jmpr,
+    Call,
+    Ret,
+    Brz,
+    Brnz,
+    Hlt,
+    Load,
+    Loadw,
+    Store,
+    Storew,
+    Inton,
+    Intoff,
+    Setiv,
+    Sdp,
+    Setsdp,
+    Pushr,
+    Popr,
+    Peekr,
+    Debug,
+}
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub struct InvalidOpcode(pub u8);
+
+impl Display for InvalidOpcode {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "Invalid opcode {:#02x}", self.0)
+    }
+}
+
+impl std::error::Error for InvalidOpcode {}
+
+impl TryFrom<u8> for Opcode {
+    type Error = InvalidOpcode;
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        use Opcode::*;
+        Ok(match value {
+            0 => Nop,
+            1 => Add,
+            2 => Sub,
+            3 => Mul,
+            4 => Div,
+            5 => Mod,
+            6 => Rand,
+            7 => And,
+            8 => Or,
+            9 => Xor,
+            10 => Not,
+            11 => Gt,
+            12 => Lt,
+            13 => Agt,
+            14 => Alt,
+            15 => Lshift,
+            16 => Rshift,
+            17 => Arshift,
+            18 => Pop,
+            19 => Dup,
+            20 => Swap,
+            21 => Pick,
+            22 => Rot,
+            23 => Jmp,
+            24 => Jmpr,
+            25 => Call,
+            26 => Ret,
+            27 => Brz,
+            28 => Brnz,
+            29 => Hlt,
+            30 => Load,
+            31 => Loadw,
+            32 => Store,
+            33 => Storew,
+            34 => Inton,
+            35 => Intoff,
+            36 => Setiv,
+            37 => Sdp,
+            38 => Setsdp,
+            39 => Pushr,
+            40 => Popr,
+            41 => Peekr,
+            42 => Debug,
+            other => return Err(InvalidOpcode(other))
+        })
+    }
+}
+
+#[test]
+fn test_decode() {
+    assert_eq!(Opcode::try_from(18), Ok(Opcode::Pop));
+    //assert_eq!(str::fmt("{}", Opcode::try_from(136).unwrap_err()), Err(InvalidOpcode(136)));
+}