diff --git a/Cargo.lock b/Cargo.lock
index 1922e57..391ab15 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -72,7 +72,7 @@ dependencies = [
 ]
 
 [[package]]
-name = "rustv64i"
+name = "rustv32i"
 version = "0.1.0"
 dependencies = [
  "aligned-vec",
diff --git a/Cargo.toml b/Cargo.toml
index e46578e..4b684f0 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,5 +1,5 @@
 [package]
-name = "rustv64i"
+name = "rustv32i"
 version = "0.1.0"
 edition = "2024"
 
diff --git a/src/emu.rs b/src/emu.rs
index c7d6c1a..f9a92f0 100644
--- a/src/emu.rs
+++ b/src/emu.rs
@@ -1,3 +1,9 @@
+use std::{
+    fmt::{Debug, Display},
+    ops::{Index, IndexMut, RangeInclusive},
+    u32,
+};
+
 use aligned_vec::{AVec, ConstAlign};
 
 use crate::PAGE_SIZE;
@@ -7,35 +13,420 @@ pub struct Memory {
 }
 
 impl Memory {
-    fn load_u32(&self, addr: u32) -> Result<u32, ()> {
-        Ok(u32::from_le_bytes(
-            self.mem
-                .get((addr as usize)..)
-                .ok_or(())?
-                .get(..4)
-                .ok_or(())?
-                .try_into()
-                .unwrap(),
-        ))
+    fn check_align(&self, addr: u32, align: u32) -> Result<(), Error> {
+        if addr % 2 != 0 {
+            Err(Error::UnaligneMemoryAccess {
+                addr,
+                required_align: align,
+            })
+        } else {
+            Ok(())
+        }
     }
+    fn index(&self, addr: u32, len: u32) -> Result<&[u8], Error> {
+        Ok(self
+            .mem
+            .get((addr as usize)..)
+            .ok_or(Error::InvalidMemoryAccess(addr))?
+            .get(..(len as usize))
+            .ok_or(Error::InvalidMemoryAccess(addr))?)
+    }
+    fn index_mut(&mut self, addr: u32, len: u32) -> Result<&mut [u8], Error> {
+        Ok(self
+            .mem
+            .get_mut((addr as usize)..)
+            .ok_or(Error::InvalidMemoryAccess(addr))?
+            .get_mut(..(len as usize))
+            .ok_or(Error::InvalidMemoryAccess(addr))?)
+    }
+
+    fn load_u8(&self, addr: u32) -> Result<u8, Error> {
+        Ok(u8::from_le_bytes(self.index(addr, 1)?.try_into().unwrap()))
+    }
+    fn load_u16(&self, addr: u32) -> Result<u16, Error> {
+        Ok(u16::from_le_bytes(self.index(addr, 2)?.try_into().unwrap()))
+    }
+    fn load_u32(&self, addr: u32) -> Result<u32, Error> {
+        Ok(u32::from_le_bytes(self.index(addr, 4)?.try_into().unwrap()))
+    }
+    fn store_u8(&mut self, addr: u32, value: u8) -> Result<(), Error> {
+        Ok(self
+            .index_mut(addr, 1)?
+            .copy_from_slice(&value.to_le_bytes()))
+    }
+    fn store_u16(&mut self, addr: u32, value: u16) -> Result<(), Error> {
+        self.check_align(addr, 2)?;
+        Ok(self
+            .index_mut(addr, 2)?
+            .copy_from_slice(&value.to_le_bytes()))
+    }
+    fn store_u32(&mut self, addr: u32, value: u32) -> Result<(), Error> {
+        self.check_align(addr, 4)?;
+        Ok(self
+            .index_mut(addr, 4)?
+            .copy_from_slice(&value.to_le_bytes()))
+    }
+}
+
+#[derive(Debug)]
+#[expect(dead_code)]
+pub enum Error {
+    IllegalInstruction(InstCode, &'static str),
+    InvalidMemoryAccess(u32),
+    UnalignedPc(u32),
+    UnaligneMemoryAccess { addr: u32, required_align: u32 },
 }
 
 pub struct Emulator {
     pub mem: Memory,
     pub xreg: [u32; 32],
+    /// Written to insterad of xreg[0].
+    pub xreg0_value: u32,
     pub pc: u32,
 }
 
+impl Index<Reg> for Emulator {
+    type Output = u32;
+
+    fn index(&self, index: Reg) -> &Self::Output {
+        &self.xreg[index.0 as usize]
+    }
+}
+impl IndexMut<Reg> for Emulator {
+    fn index_mut(&mut self, index: Reg) -> &mut Self::Output {
+        if index.0 == 0 {
+            &mut self.xreg0_value
+        } else {
+            &mut self.xreg[index.0 as usize]
+        }
+    }
+}
+
+struct Reg(u32);
+
+impl Reg {
+    const RA: Reg = Reg(1);
+    const SP: Reg = Reg(2);
+}
+
+impl Display for Reg {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        if self.0 == Self::SP.0 {
+            write!(f, "sp")
+        } else if self.0 == Self::RA.0 {
+            write!(f, "ra")
+        } else {
+            write!(f, "x{}", self.0)
+        }
+    }
+}
+
+enum Inst {
+    Jal { offset: u32, dest: Reg },
+    Jalr { offset: u32, base: Reg, dest: Reg },
+
+    Lb { offset: u32, dest: Reg, base: Reg },
+    Lbu { offset: u32, dest: Reg, base: Reg },
+    Lh { offset: u32, dest: Reg, base: Reg },
+    Lhu { offset: u32, dest: Reg, base: Reg },
+    Lw { offset: u32, dest: Reg, base: Reg },
+
+    Sb { offset: u32, src: Reg, base: Reg },
+    Sh { offset: u32, src: Reg, base: Reg },
+    Sw { offset: u32, src: Reg, base: Reg },
+
+    Addi { imm: u32, rd: Reg, rs1: Reg },
+    Slti { imm: u32, rd: Reg, rs1: Reg },
+    Sltiu { imm: u32, rd: Reg, rs1: Reg },
+    Andi { imm: u32, rd: Reg, rs1: Reg },
+    Ori { imm: u32, rd: Reg, rs1: Reg },
+    Xori { imm: u32, rd: Reg, rs1: Reg },
+}
+
+fn sign_extend(value: u32, size: u32) -> u32 {
+    assert!(size <= u32::BITS);
+    let sign = value >> (size - 1);
+    let imm = if sign == 1 {
+        (u32::MAX << size) | value
+    } else {
+        value
+    };
+    imm
+}
+
+#[derive(Clone, Copy)]
+pub struct InstCode(u32);
+
+impl InstCode {
+    fn extract(self, range: RangeInclusive<u32>) -> u32 {
+        let end_span = 32 - (range.end() + 1);
+        (self.0 << (end_span)) >> (end_span + range.start())
+    }
+
+    fn opcode(self) -> u32 {
+        self.0 & 0b1111111
+    }
+    fn funct3(self) -> u32 {
+        self.extract(12..=14)
+    }
+    fn rs1(self) -> Reg {
+        Reg(self.extract(15..=19))
+    }
+    fn rs2(self) -> Reg {
+        Reg(self.extract(20..=24))
+    }
+    fn rd(self) -> Reg {
+        Reg(self.extract(7..=11))
+    }
+    fn imm_i(self) -> u32 {
+        let imm = self.extract(20..=31);
+        sign_extend(imm, 12)
+    }
+    fn imm_j(self) -> u32 {
+        let imm_20 = self.extract(31..=31);
+        let imm_10_1 = self.extract(21..=30);
+        let imm_19_12 = self.extract(12..=19);
+        let imm = (imm_20 << 19) | (imm_19_12 << 11) | imm_10_1;
+        sign_extend(imm, 20)
+    }
+    fn imm_s(self) -> u32 {
+        let imm_11_5 = self.extract(25..=31);
+        let imm_4_0 = self.extract(7..=11);
+        let full_imm = (imm_11_5 << 5) | imm_4_0;
+        sign_extend(full_imm, 12)
+    }
+}
+
+impl Debug for InstCode {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:0>32b}", self.0)
+    }
+}
+
+impl Inst {
+    fn decode(code: InstCode) -> Result<Inst, Error> {
+        eprintln!("decoding: {code:?}");
+        let inst = match code.opcode() {
+            // JAL
+            0b1101111 => Inst::Jal {
+                offset: code.imm_j(),
+                dest: code.rd(),
+            },
+            // JALR
+            0b1100111 => match code.funct3() {
+                0b000 => Inst::Jalr {
+                    offset: code.imm_i(),
+                    base: code.rs1(),
+                    dest: code.rd(),
+                },
+                _ => return Err(Error::IllegalInstruction(code, "funct3")),
+            },
+            // LOAD
+            0b0000011 => match code.funct3() {
+                0b000 => Inst::Lb {
+                    offset: code.imm_i(),
+                    dest: code.rd(),
+                    base: code.rs1(),
+                },
+                0b001 => Inst::Lh {
+                    offset: code.imm_i(),
+                    dest: code.rd(),
+                    base: code.rs1(),
+                },
+                0b010 => Inst::Lw {
+                    offset: code.imm_i(),
+                    dest: code.rd(),
+                    base: code.rs1(),
+                },
+                0b100 => Inst::Lbu {
+                    offset: code.imm_i(),
+                    dest: code.rd(),
+                    base: code.rs1(),
+                },
+                0b101 => Inst::Lhu {
+                    offset: code.imm_i(),
+                    dest: code.rd(),
+                    base: code.rs1(),
+                },
+                _ => return Err(Error::IllegalInstruction(code, "funct3")),
+            },
+            // STORE
+            0b0100011 => match code.funct3() {
+                0b000 => Inst::Sb {
+                    offset: code.imm_s(),
+                    src: code.rs2(),
+                    base: code.rs1(),
+                },
+                0b001 => Inst::Sh {
+                    offset: code.imm_s(),
+                    src: code.rs2(),
+                    base: code.rs1(),
+                },
+                0b010 => Inst::Sw {
+                    offset: code.imm_s(),
+                    src: code.rs2(),
+                    base: code.rs1(),
+                },
+                _ => return Err(Error::IllegalInstruction(code, "funct3")),
+            },
+            // OP-IMM
+            0b0010011 => match code.funct3() {
+                0b000 => Inst::Addi {
+                    imm: code.imm_i(),
+                    rd: code.rd(),
+                    rs1: code.rs1(),
+                },
+                0b010 => Inst::Slti {
+                    imm: code.imm_i(),
+                    rd: code.rd(),
+                    rs1: code.rs1(),
+                },
+                0b011 => Inst::Sltiu {
+                    imm: code.imm_i(),
+                    rd: code.rd(),
+                    rs1: code.rs1(),
+                },
+                0b100 => Inst::Xori {
+                    imm: code.imm_i(),
+                    rd: code.rd(),
+                    rs1: code.rs1(),
+                },
+                0b110 => Inst::Ori {
+                    imm: code.imm_i(),
+                    rd: code.rd(),
+                    rs1: code.rs1(),
+                },
+                0b111 => Inst::Andi {
+                    imm: code.imm_i(),
+                    rd: code.rd(),
+                    rs1: code.rs1(),
+                },
+                _ => return Err(Error::IllegalInstruction(code, "funct3")),
+            },
+            _ => return Err(Error::IllegalInstruction(code, "opcode")),
+        };
+        eprintln!("  parsed {inst:?}");
+        Ok(inst)
+    }
+}
+
+impl Debug for Inst {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        Display::fmt(&self, f)
+    }
+}
+impl Display for Inst {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Inst::Jal { offset, dest } => write!(f, "jal {dest}, {offset}"),
+            Inst::Jalr { offset, base, dest } => write!(f, "jalr {dest}, {offset}({base})"),
+            Inst::Lb { offset, dest, base } => write!(f, "lb {dest}, {offset}({base})"),
+            Inst::Lbu { offset, dest, base } => write!(f, "lbu {dest}, {offset}({base})"),
+            Inst::Lh { offset, dest, base } => write!(f, "lh {dest}, {offset}({base})"),
+            Inst::Lhu { offset, dest, base } => write!(f, "lhu {dest}, {offset}({base})"),
+            Inst::Lw { offset, dest, base } => write!(f, "lw {dest}, {offset}({base})"),
+            Inst::Sb { offset, src, base } => write!(f, "sb {src}, {offset}({base})"),
+            Inst::Sh { offset, src, base } => write!(f, "sh {src}, {offset}({base})"),
+            Inst::Sw { offset, src, base } => write!(f, "sw {src}, {offset}({base})"),
+            Inst::Addi { imm, rd, rs1 } => write!(f, "addi {rd}, {rs1}, {}", *imm as i32),
+            Inst::Slti { imm, rd, rs1 } => write!(f, "slti {rd}, {rs1}, {}", *imm as i32),
+            Inst::Sltiu { imm, rd, rs1 } => write!(f, "sltiu {rd}, {rs1}, {}", *imm as i32),
+            Inst::Andi { imm, rd, rs1 } => write!(f, "andi {rd}, {rs1}, {}", *imm as i32),
+            Inst::Ori { imm, rd, rs1 } => write!(f, "ori {rd}, {rs1}, {}", *imm as i32),
+            Inst::Xori { imm, rd, rs1 } => write!(f, "xori {rd}, {rs1}, {}", *imm as i32),
+        }
+    }
+}
+
 impl Emulator {
-    pub fn execute(&mut self) -> Result<(), ()> {
+    pub fn start_linux(&mut self) -> Result<(), Error> {
+        // set top of stack. just some yolo address. with no values there. who needs abi?
+        self[Reg::SP] = 4096;
+
         loop {
-            self.step();
+            self.step()?;
         }
     }
 
-    fn step(&mut self) -> Result<(), ()> {
+    fn set_pc(&mut self, pc: u32) -> Result<(), Error> {
+        if pc % 4 != 0 {
+            return Err(Error::UnalignedPc(pc));
+        }
+        self.pc = pc;
+        Ok(())
+    }
+
+    fn step(&mut self) -> Result<(), Error> {
         let instruction = self.mem.load_u32(self.pc)?;
 
-        todo!()
+        let instruction = Inst::decode(InstCode(instruction))?;
+
+        match instruction {
+            Inst::Jal { offset, dest } => {
+                let target = self.pc.wrapping_add(offset);
+                self[dest] = self.pc.wrapping_add(4);
+                self.set_pc(target)?;
+            }
+            Inst::Jalr { offset, base, dest } => {
+                let target = self[base].wrapping_add(offset.wrapping_mul(2)) & !1;
+                self[dest] = self.pc.wrapping_add(4);
+                self.set_pc(target)?;
+            }
+            Inst::Lb { offset, dest, base } => {
+                let addr = self[base].wrapping_add(offset);
+                self[dest] = self.mem.load_u8(addr)? as i8 as i32 as u32;
+            }
+            Inst::Lbu { offset, dest, base } => {
+                let addr = self[base].wrapping_add(offset);
+                self[dest] = self.mem.load_u8(addr)? as u32;
+            }
+            Inst::Lh { offset, dest, base } => {
+                let addr = self[base].wrapping_add(offset);
+                self[dest] = self.mem.load_u16(addr)? as i16 as i32 as u32;
+            }
+            Inst::Lhu { offset, dest, base } => {
+                let addr = self[base].wrapping_add(offset);
+                self[dest] = self.mem.load_u8(addr)? as u32;
+            }
+            Inst::Lw { offset, dest, base } => {
+                let addr = self[base].wrapping_add(offset);
+                self[dest] = self.mem.load_u32(addr)?;
+            }
+            Inst::Sb { offset, src, base } => {
+                let addr = self[base].wrapping_add(offset);
+                self.mem.store_u8(addr, self[src] as u8)?;
+            }
+            Inst::Sh { offset, src, base } => {
+                let addr = self[base].wrapping_add(offset);
+                self.mem.store_u16(addr, self[src] as u16)?;
+            }
+            Inst::Sw { offset, src, base } => {
+                let addr = self[base].wrapping_add(offset);
+                self.mem.store_u32(addr, self[src] as u32)?;
+            }
+            Inst::Addi { imm, rd, rs1 } => {
+                self[rd] = self[rs1].wrapping_add(imm as u32);
+            }
+            Inst::Slti { imm, rd, rs1 } => {
+                let result = (self[rs1] as i32) < (imm as i32);
+                self[rd] = result as u32;
+            }
+            Inst::Sltiu { imm, rd, rs1 } => {
+                let result = (self[rs1] as u32) < imm as u32;
+                self[rd] = result as u32;
+            }
+            Inst::Andi { imm, rd, rs1 } => {
+                self[rd] = self[rs1] & imm;
+            }
+            Inst::Ori { imm, rd, rs1 } => {
+                self[rd] = self[rs1] | imm;
+            }
+            Inst::Xori { imm, rd, rs1 } => {
+                self[rd] = self[rs1] ^ imm;
+            }
+        }
+
+        self.set_pc(self.pc + 4)?;
+        Ok(())
     }
 }
diff --git a/src/main.rs b/src/main.rs
index e767cdf..f6887b5 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -63,9 +63,10 @@ fn main() -> eyre::Result<()> {
     let mut emu = emu::Emulator {
         mem,
         xreg: [0; 32],
+        xreg0_value: 0,
         pc: start,
     };
-    emu.execute().unwrap();
+    emu.start_linux().unwrap();
 
     Ok(())
 }
diff --git a/test/Makefile b/test/Makefile
index db66864..ad2b298 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -1,5 +1,5 @@
-CC = clang -target riscv32-unknown-linux-gnu -fuse-ld=lld -march=rv32i
+CC = clang -Wall -Wpedantic -target riscv32-unknown-linux-gnu -fuse-ld=lld -march=rv32i
 CC_STATIC = $(CC) -static -nostdlib -nodefaultlibs
 
-test: test.c
-	$(CC_STATIC) test.c -o test
+init: init.c
+	$(CC_STATIC) init.c -o init
diff --git a/test/init.c b/test/init.c
new file mode 100644
index 0000000..6d147da
--- /dev/null
+++ b/test/init.c
@@ -0,0 +1,11 @@
+void _start(void)
+{
+    __asm__ volatile (
+        "li a7, 93;" // exit
+        "li a0, 0;" // code 0
+        "ecall"
+        :
+        :
+        : "a7", "a0", "memory"
+    );
+}
diff --git a/test/test.c b/test/test.c
deleted file mode 100644
index c0f319a..0000000
--- a/test/test.c
+++ /dev/null
@@ -1,3 +0,0 @@
-void _start()
-{
-}