diff --git a/Makefile b/Makefile
index 59a8e6e..9715e5b 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,6 @@ U=user
 
 OBJS = \
   $K/entry.o \
-  $K/start.o \
   $K/console.o \
   $K/printf.o \
   $K/kalloc.o \
diff --git a/kernel/entry.S b/kernel/entry.S
index 5ab365e..574dfd0 100644
--- a/kernel/entry.S
+++ b/kernel/entry.S
@@ -5,8 +5,8 @@
 .section .text
 .global _entry
 _entry:
-        # set up a stack for C.
-        # stack0 is declared in start.c,
+        # set up a stack for Rust
+        # stack0 is declared in start.rs,
         # with a 4096-byte stack per CPU.
         # sp = stack0 + (hartid * 4096)
         la sp, stack0
@@ -15,7 +15,7 @@ _entry:
         addi a1, a1, 1
         mul a0, a0, a1
         add sp, sp, a0
-        # jump to start() in start.c
+        # jump to start() in start.rs
         call start
 spin:
         j spin
diff --git a/kernel/start.c b/kernel/start.c
deleted file mode 100644
index f83b619..0000000
--- a/kernel/start.c
+++ /dev/null
@@ -1,85 +0,0 @@
-#include "types.h"
-#include "param.h"
-#include "memlayout.h"
-#include "riscv.h"
-#include "defs.h"
-
-void main();
-void timerinit();
-
-// entry.S needs one stack per CPU.
-__attribute__((aligned(16))) char stack0[4096 * NCPU];
-
-// a scratch area per CPU for machine-mode timer interrupts.
-uint64 timer_scratch[NCPU][5];
-
-// assembly code in kernelvec.S for machine-mode timer interrupt.
-extern void timervec();
-
-// entry.S jumps here in machine mode on stack0.
-void start() {
-	// set M Previous Privilege mode to Supervisor, for mret.
-	unsigned long x = r_mstatus();
-	x &= ~MSTATUS_MPP_MASK;
-	x |= MSTATUS_MPP_S;
-	w_mstatus(x);
-
-	// set M Exception Program Counter to main, for mret.
-	// requires gcc -mcmodel=medany
-	w_mepc((uint64)main);
-
-	// disable paging for now.
-	w_satp(0);
-
-	// delegate all interrupts and exceptions to supervisor mode.
-	w_medeleg(0xffff);
-	w_mideleg(0xffff);
-	w_sie(r_sie() | SIE_SEIE | SIE_STIE | SIE_SSIE);
-
-	// configure Physical Memory Protection to give supervisor mode
-	// access to all of physical memory.
-	w_pmpaddr0(0x3fffffffffffffull);
-	w_pmpcfg0(0xf);
-
-	// ask for clock interrupts.
-	timerinit();
-
-	// keep each CPU's hartid in its tp register, for cpuid().
-	int id = r_mhartid();
-	w_tp(id);
-
-	// switch to supervisor mode and jump to main().
-	asm volatile("mret");
-}
-
-// arrange to receive timer interrupts.
-// they will arrive in machine mode at
-// at timervec in kernelvec.S,
-// which turns them into software interrupts for
-// devintr() in trap.c.
-void timerinit() {
-	// each CPU has a separate source of timer interrupts.
-	int id = r_mhartid();
-
-	// ask the CLINT for a timer interrupt.
-	int interval = 1000000; // cycles; about 1/10th second in qemu.
-	*(uint64 *)CLINT_MTIMECMP(id) = *(uint64 *)CLINT_MTIME + interval;
-
-	// prepare information in scratch[] for timervec.
-	// scratch[0..2] : space for timervec to save registers.
-	// scratch[3] : address of CLINT MTIMECMP register.
-	// scratch[4] : desired interval (in cycles) between timer interrupts.
-	uint64 *scratch = &timer_scratch[id][0];
-	scratch[3] = CLINT_MTIMECMP(id);
-	scratch[4] = interval;
-	w_mscratch((uint64)scratch);
-
-	// set the machine-mode trap handler.
-	w_mtvec((uint64)timervec);
-
-	// enable machine-mode interrupts.
-	w_mstatus(r_mstatus() | MSTATUS_MIE);
-
-	// enable machine-mode timer interrupts.
-	w_mie(r_mie() | MIE_MTIE);
-}
diff --git a/theseus/src/lib.rs b/theseus/src/lib.rs
index 4f91dd2..59c5e02 100644
--- a/theseus/src/lib.rs
+++ b/theseus/src/lib.rs
@@ -2,8 +2,10 @@
 #![crate_type = "staticlib"]
 
 pub mod memlayout;
+pub mod param;
 pub mod riscv;
 pub mod spinlock;
+pub mod start;
 pub mod uart;
 
 extern "C" {
diff --git a/theseus/src/memlayout.rs b/theseus/src/memlayout.rs
index 114ca5d..4e34cdf 100644
--- a/theseus/src/memlayout.rs
+++ b/theseus/src/memlayout.rs
@@ -28,13 +28,12 @@ pub const VIRTIO0: i32 = 0x10001000;
 pub const VIRTIO0_IRQ: i32 = 1;
 
 // core local interruptor (CLINT), which contains the timer.
-pub const CLINT: i64 = 0x2000000;
-// const CLINT_MTIMECMP(hartid) (CLINT + 0x4000 + 8 * (hartid));
+pub const CLINT: u64 = 0x2000000;
 #[inline]
-pub fn CLINT_MTIMECMP(hartid: i32) -> i64 {
-	CLINT + 0x4000 + 8 * hartid as i64
+pub fn CLINT_MTIMECMP(hartid: u64) -> *mut u64 {
+	(CLINT + 0x4000 + 8 * hartid) as *mut u64
 }
-pub const CLINT_MTIME: i64 = CLINT + 0xBFF8; // cycles since boot.
+pub const CLINT_MTIME: *mut u64 = (CLINT + 0xBFF8) as *mut u64; // cycles since boot.
 
 // qemu puts platform-level interrupt controller (PLIC) here.
 pub const PLIC: i64 = 0x0c000000;
diff --git a/theseus/src/param.rs b/theseus/src/param.rs
new file mode 100644
index 0000000..17b1369
--- /dev/null
+++ b/theseus/src/param.rs
@@ -0,0 +1,13 @@
+pub const NPROC: usize = 64; // maximum number of processes
+pub const NCPU: usize = 8; // maximum number of CPUs
+pub const NOFILE: usize = 16; // open files per process
+pub const NFILE: usize = 100; // open files per system
+pub const NINODE: usize = 50; // maximum number of active i-nodes
+pub const NDEV: usize = 10; // maximum major device number
+pub const ROOTDEV: usize = 1; // device number of file system root disk
+pub const MAXARG: usize = 32; // max exec arguments
+pub const MAXOPBLOCKS: usize = 10; // max # of blocks any FS op writes
+pub const LOGSIZE: usize = MAXOPBLOCKS * 3; // max data blocks in on-disk log
+pub const NBUF: usize = MAXOPBLOCKS * 3; // size of disk block cache
+pub const FSSIZE: usize = 2000; // size of file system in blocks
+pub const MAXPATH: usize = 128; // maximum file path name
diff --git a/theseus/src/riscv.rs b/theseus/src/riscv.rs
index 4a16823..94994d2 100644
--- a/theseus/src/riscv.rs
+++ b/theseus/src/riscv.rs
@@ -1,3 +1,282 @@
+use core::arch::asm;
+
+// which hart (core) is this?
+#[inline]
+pub unsafe fn r_mhartid() -> u64 {
+	let x: u64;
+	asm!("csrr {x}, mhartid", x = out(reg) x);
+	x
+}
+
+// Machine Status Register, mstatus
+pub const MSTATUS_MPP_MASK: u64 = 3 << 11; // previous mode.
+pub const MSTATUS_MPP_M: u64 = 3 << 11;
+pub const MSTATUS_MPP_S: u64 = 1 << 11;
+pub const MSTATUS_MPP_U: u64 = 0 << 11;
+pub const MSTATUS_MIE: u64 = 1 << 3; // machine-mode interrupt enable.
+
+#[inline]
+pub unsafe fn r_mstatus() -> u64 {
+	let x: u64;
+	asm!("csrr {x}, mstatus", x = out(reg) x);
+	x
+}
+
+#[inline]
+pub unsafe fn w_mstatus(x: u64) {
+	asm!("csrw mstatus, {x}", x = in(reg) x);
+}
+
+// // machine exception program counter, holds the
+// // instruction address to which a return from
+// // exception will go.
+#[inline]
+pub unsafe fn w_mepc(x: u64) {
+	asm!("csrw mepc, {x}", x = in(reg) x);
+}
+
+// // Supervisor Status Register, sstatus
+
+// #define SSTATUS_SPP (1L << 8)  // Previous mode, 1=Supervisor, 0=User
+// #define SSTATUS_SPIE (1L << 5) // Supervisor Previous Interrupt Enable
+// #define SSTATUS_UPIE (1L << 4) // User Previous Interrupt Enable
+// #define SSTATUS_SIE (1L << 1)  // Supervisor Interrupt Enable
+// #define SSTATUS_UIE (1L << 0)  // User Interrupt Enable
+
+#[inline]
+pub unsafe fn r_sstatus() -> u64 {
+	let x: u64;
+	asm!("csrr {x}, sstatus", x = out(reg) x);
+	x
+}
+
+#[inline]
+pub unsafe fn w_sstatus(x: u64) {
+	asm!("csrw sstatus, {x}", x = in(reg) x);
+}
+
+// // Supervisor Interrupt Pending
+#[inline]
+pub unsafe fn r_sip() -> u64 {
+	let x: u64;
+	asm!("csrr {x}, sip", x = out(reg) x);
+	x
+}
+
+// static inline void w_sip(uint64 x) { asm volatile("csrw sip, %0" : : "r"(x)); }
+#[inline]
+pub unsafe fn w_sip(x: u64) {
+	asm!("csrw sip, {x}", x = in(reg) x);
+}
+
+// Supervisor Interrupt Enable
+pub const SIE_SEIE: u64 = 1 << 9; // external
+pub const SIE_STIE: u64 = 1 << 5; // timer
+pub const SIE_SSIE: u64 = 1 << 1; // software
+
+// static inline uint64 r_sie() {
+// 	uint64 x;
+// 	asm volatile("csrr %0, sie" : "=r"(x));
+// 	return x;
+// }
+#[inline]
+pub unsafe fn r_sie() -> u64 {
+	let x: u64;
+	asm!("csrr {x}, sie", x = out(reg) x);
+	x
+}
+
+// static inline void w_sie(uint64 x) { asm volatile("csrw sie, %0" : : "r"(x)); }
+#[inline]
+pub unsafe fn w_sie(x: u64) {
+	asm!("csrw sie, {x}", x = in(reg) x);
+}
+
+// // Machine-mode Interrupt Enable
+pub const MIE_MEIE: u64 = 1 << 11; // external
+pub const MIE_MTIE: u64 = 1 << 7; // timer
+pub const MIE_MSIE: u64 = 1 << 3; // software
+
+#[inline]
+pub unsafe fn r_mie() -> u64 {
+	let x: u64;
+	asm!("csrr {x}, mie", x = out(reg) x);
+	x
+}
+
+#[inline]
+pub unsafe fn w_mie(x: u64) {
+	asm!("csrw mie, {x}", x = in(reg) x);
+}
+
+// // supervisor exception program counter, holds the
+// // instruction address to which a return from
+// // exception will go.
+// static inline void w_sepc(uint64 x) {
+// 	asm volatile("csrw sepc, %0" : : "r"(x));
+// }
+
+// static inline uint64 r_sepc() {
+// 	uint64 x;
+// 	asm volatile("csrr %0, sepc" : "=r"(x));
+// 	return x;
+// }
+
+// // Machine Exception Delegation
+// static inline uint64 r_medeleg() {
+// 	uint64 x;
+// 	asm volatile("csrr %0, medeleg" : "=r"(x));
+// 	return x;
+// }
+
+#[inline]
+pub unsafe fn w_medeleg(x: u64) {
+	asm!("csrw medeleg, {x}", x = in(reg) x);
+}
+
+// // Machine Interrupt Delegation
+// static inline uint64 r_mideleg() {
+// 	uint64 x;
+// 	asm volatile("csrr %0, mideleg" : "=r"(x));
+// 	return x;
+// }
+
+#[inline]
+pub unsafe fn w_mideleg(x: u64) {
+	asm!("csrw mideleg, {x}", x = in(reg) x);
+}
+
+// // Supervisor Trap-Vector Base Address
+// // low two bits are mode.
+// static inline void w_stvec(uint64 x) {
+// 	asm volatile("csrw stvec, %0" : : "r"(x));
+// }
+
+// static inline uint64 r_stvec() {
+// 	uint64 x;
+// 	asm volatile("csrr %0, stvec" : "=r"(x));
+// 	return x;
+// }
+
+// // Machine-mode interrupt vector
+#[inline]
+pub unsafe fn w_mtvec(x: u64) {
+	asm!("csrw mtvec, {x}", x = in(reg) x);
+}
+
+// Physical Memory Protection
+#[inline]
+pub unsafe fn w_pmpcfg0(x: u64) {
+	asm!("csrw pmpcfg0, {x}", x = in(reg) x);
+}
+
+#[inline]
+pub unsafe fn w_pmpaddr0(x: u64) {
+	asm!("csrw pmpaddr0, {x}", x = in(reg) x);
+}
+
+// // use riscv's sv39 page table scheme.
+// #define SATP_SV39 (8L << 60)
+
+// #define MAKE_SATP(pagetable) (SATP_SV39 | (((uint64)pagetable) >> 12))
+
+// supervisor address translation and protection;
+// holds the address of the page table.
+#[inline]
+pub unsafe fn w_satp(x: u64) {
+	asm!("csrw satp, {x}", x = in(reg) x);
+}
+
+// static inline uint64 r_satp() {
+// 	uint64 x;
+// 	asm volatile("csrr %0, satp" : "=r"(x));
+// 	return x;
+// }
+
+#[inline]
+pub unsafe fn w_mscratch(x: u64) {
+	asm!("csrw mscratch, {x}", x = in(reg) x);
+}
+
+// // Supervisor Trap Cause
+// static inline uint64 r_scause() {
+// 	uint64 x;
+// 	asm volatile("csrr %0, scause" : "=r"(x));
+// 	return x;
+// }
+
+// // Supervisor Trap Value
+// static inline uint64 r_stval() {
+// 	uint64 x;
+// 	asm volatile("csrr %0, stval" : "=r"(x));
+// 	return x;
+// }
+
+// // Machine-mode Counter-Enable
+// static inline void w_mcounteren(uint64 x) {
+// 	asm volatile("csrw mcounteren, %0" : : "r"(x));
+// }
+
+// static inline uint64 r_mcounteren() {
+// 	uint64 x;
+// 	asm volatile("csrr %0, mcounteren" : "=r"(x));
+// 	return x;
+// }
+
+// // machine-mode cycle counter
+// static inline uint64 r_time() {
+// 	uint64 x;
+// 	asm volatile("csrr %0, time" : "=r"(x));
+// 	return x;
+// }
+
+// // enable device interrupts
+// static inline void intr_on() { w_sstatus(r_sstatus() | SSTATUS_SIE); }
+
+// // disable device interrupts
+// static inline void intr_off() { w_sstatus(r_sstatus() & ~SSTATUS_SIE); }
+
+// // are device interrupts enabled?
+// static inline int intr_get() {
+// 	uint64 x = r_sstatus();
+// 	return (x & SSTATUS_SIE) != 0;
+// }
+
+// static inline uint64 r_sp() {
+// 	uint64 x;
+// 	asm volatile("mv %0, sp" : "=r"(x));
+// 	return x;
+// }
+
+// // read and write tp, the thread pointer, which xv6 uses to hold
+// // this core's hartid (core number), the index into cpus[].
+// static inline uint64 r_tp() {
+// 	uint64 x;
+// 	asm volatile("mv %0, tp" : "=r"(x));
+// 	return x;
+// }
+
+// static inline void w_tp(uint64 x) { asm volatile("mv tp, %0" : : "r"(x)); }
+#[inline]
+pub unsafe fn w_tp(x: u64) {
+	asm!("mv tp, {x}", x = in(reg) x);
+}
+
+// static inline uint64 r_ra() {
+// 	uint64 x;
+// 	asm volatile("mv %0, ra" : "=r"(x));
+// 	return x;
+// }
+
+// // flush the TLB.
+// static inline void sfence_vma() {
+// 	// the zero, zero means flush all TLB entries.
+// 	asm volatile("sfence.vma zero, zero");
+// }
+
+// typedef uint64 pte_t;
+// typedef uint64 *pagetable_t; // 512 PTEs
+
 pub const PGSIZE: u64 = 4096; // bytes per page
 pub const PGSHIFT: i32 = 12; // bits of offset within a page
 
diff --git a/theseus/src/start.rs b/theseus/src/start.rs
new file mode 100644
index 0000000..9f095d6
--- /dev/null
+++ b/theseus/src/start.rs
@@ -0,0 +1,94 @@
+use core::arch::asm;
+use core::usize;
+
+use crate::memlayout::{CLINT_MTIME, CLINT_MTIMECMP};
+use crate::param::NCPU;
+use crate::riscv as rv;
+
+extern "C" {
+	// assembly code in kernelvec.S for machine-mode timer interrupt.
+	fn timervec();
+
+	// main.c
+	fn main();
+}
+
+#[repr(align(16))]
+pub struct EntryStack([u8; 4096 * NCPU]);
+
+// entry.S needs one stack per CPU.
+#[no_mangle]
+pub static mut stack0: EntryStack = EntryStack([0; 4096 * NCPU]);
+
+// a scratch area per CPU for machine-mode timer interrupts.
+static mut timer_scratch: [[u64; 5]; NCPU] = [[0; 5]; NCPU];
+
+// entry.S jumps here in machine mode on stack0.
+#[no_mangle]
+pub unsafe extern "C" fn start() {
+	// set M Previous Privilege mode to Supervisor, for mret.
+	let mut x = rv::r_mstatus();
+	x &= !rv::MSTATUS_MPP_MASK;
+	x |= rv::MSTATUS_MPP_S;
+	rv::w_mstatus(x);
+
+	// set M Exception Program Counter to main, for mret.
+	// requires gcc -mcmodel=medany
+	rv::w_mepc(main as *const () as u64);
+
+	// disable paging for now.
+	rv::w_satp(0);
+
+	// delegate all interrupts and exceptions to supervisor mode.
+	rv::w_medeleg(0xffff);
+	rv::w_mideleg(0xffff);
+	rv::w_sie(rv::r_sie() | rv::SIE_SEIE | rv::SIE_STIE | rv::SIE_SSIE);
+
+	// configure Physical Memory Protection to give supervisor mode
+	// access to all of physical memory.
+	rv::w_pmpaddr0(0x3fffffffffffff);
+	rv::w_pmpcfg0(0xf);
+
+	// ask for clock interrupts.
+	timerinit();
+
+	// keep each CPU's hartid in its tp register, for cpuid().
+	let id = rv::r_mhartid();
+	rv::w_tp(id);
+
+	// switch to supervisor mode and jump to main().
+	asm!("mret");
+}
+
+// arrange to receive timer interrupts.
+// they will arrive in machine mode at
+// at timervec in kernelvec.S,
+// which turns them into software interrupts for
+// devintr() in trap.c.
+unsafe fn timerinit() {
+	// each CPU has a separate source of timer interrupts.
+	let id = rv::r_mhartid();
+
+	// ask the CLINT for a timer interrupt.
+	let interval: u64 = 1000000; // cycles; about 1/10th second in qemu.
+	*CLINT_MTIMECMP(id) = *CLINT_MTIME + interval;
+
+	// prepare information in scratch[] for timervec.
+	// scratch[0..2] : space for timervec to save registers.
+	// scratch[3] : address of CLINT MTIMECMP register.
+	// scratch[4] : desired interval (in cycles) between timer interrupts.
+	timer_scratch[id as usize][3] = CLINT_MTIMECMP(id) as u64;
+	timer_scratch[id as usize][4] = interval;
+
+	// w_mscratch((uint64)scratch);
+	rv::w_mscratch(timer_scratch[id as usize].as_ptr() as u64);
+
+	// set the machine-mode trap handler.
+	rv::w_mtvec(timervec as *const () as u64);
+
+	// enable machine-mode interrupts.
+	rv::w_mstatus(rv::r_mstatus() | rv::MSTATUS_MIE);
+
+	// enable machine-mode timer interrupts.
+	rv::w_mie(rv::r_mie() | rv::MIE_MTIE);
+}