diff --git a/Cargo.toml b/Cargo.toml
index 7887b0b..6ac48dd 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,5 +9,4 @@ keywords = ["riscv", "register", "peripheral"]
 license = "ISC"
 
 [dependencies]
-bare-metal = "^0.1.1"
-volatile-register = "^0.2.0"
\ No newline at end of file
+bare-metal = "0.1.1"
\ No newline at end of file
diff --git a/README.md b/README.md
index 79424ad..93fb329 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,85 @@
 
 > Low level access to RISCV processors
 
+## Implemented Peripherals
+- [ ] plic
+- [ ] clint
+
+## Implemented privileged ASM instructions
+- [x] ecall
+- [x] ebreak
+- [x] uret
+- [x] sret
+- [x] mret
+- [x] wfi
+- [ ] sfence.vma
+
+## Implemented CSR's
+
+### User mode
+- [ ] ustatus
+- [ ] uie
+- [ ] utvec
+- [ ] uscratch
+- [ ] uepc
+- [ ] ucause
+- [ ] utval
+- [ ] uip
+- [ ] fflags
+- [ ] frm
+- [ ] fcsr
+- [ ] cycle
+- [ ] time
+- [ ] instret
+- [ ] hpmcounter[3-31]
+- [ ] cycleh
+- [ ] timeh
+- [ ] instreth
+- [ ] hpmcounter[3-31]h
+
+### Supervisor mode
+- [ ] sstatus
+- [ ] sedeleg
+- [ ] sideleg
+- [ ] sie
+- [ ] stvec
+- [ ] scounteren
+- [ ] sscratch
+- [ ] sepc
+- [ ] scause
+- [ ] stval
+- [ ] sip
+- [ ] satp
+
+### Machine mode
+- [x] mvendorid
+- [ ] marchid
+- [ ] mimpid
+- [ ] mhartid
+- [x] mstatus
+- [x] misa
+- [ ] medeleg
+- [ ] mideleg
+- [x] mie
+- [x] mtvec
+- [ ] mcounteren
+- [ ] mscratch
+- [ ] mepc
+- [x] mcause
+- [ ] mtval
+- [x] mip
+- [ ] pmpcfg[0-3]
+- [ ] pmpaddr[0-15]
+- [x] mcycle
+- [x] minstret
+- [ ] mhpmcounter[3-31]
+- [x] mcycleh
+- [x] minstreth
+- [ ] mhpmcounter[3-31]h
+- [ ] mhpmevent[3-31]
+- [ ] tselect
+- [ ] tdata[1-3]
+
 # License
 Copyright 2017 David Craven
 
diff --git a/src/asm.rs b/src/asm.rs
index a50b623..7f29cd5 100644
--- a/src/asm.rs
+++ b/src/asm.rs
@@ -17,16 +17,10 @@ macro_rules! instruction {
 }
 
 
-/// User Level ISA instructions
-instruction!(nop, "addi zero, zero, 0");
+/// Priviledged ISA Instructions
 instruction!(ecall, "ecall");
 instruction!(ebreak, "ebreak");
-instruction!(fence, "fence iorw, iorw");
-instruction!(fencei, "fence.i");
-
-/// Priviledged ISA Instructions
-instruction!(wfi, "wfi");
 instruction!(uret, "uret");
 instruction!(sret, "sret");
 instruction!(mret, "mret");
-instruction!(sfencevma, "sfence.vma");
+instruction!(wfi, "wfi");
diff --git a/src/csr.rs b/src/csr.rs
deleted file mode 100644
index 4ef9e1c..0000000
--- a/src/csr.rs
+++ /dev/null
@@ -1,606 +0,0 @@
-//! Functions for accessing Control and Status Registers
-
-#[cfg(target_arch = "riscv")]
-macro_rules! csr_asm {
-    ($op:ident, $csr:expr, $value:expr) => (
-        {
-            let res: usize;
-            unsafe {
-                asm!(concat!(stringify!($op), " $0, ", stringify!($csr), ", $1")
-                     : "=r"(res)
-                     : "r"($value)
-                     :
-                     : "volatile");
-            }
-            res
-        }
-    )
-}
-
-
-#[cfg(not(target_arch = "riscv"))]
-macro_rules! csr_asm {
-    ($op:ident, $csr:expr, $value:expr) => {
-        0
-    }
-}
-
-macro_rules! r {
-    ($MOD:ident, $TYPE:ident, $CSR:expr) => (
-        pub struct R {
-            bits: u32,
-        }
-
-        impl super::$TYPE {
-            #[inline]
-            pub fn read(&self) -> R {
-                R { bits: csr_asm!(csrrs, $CSR, 0) as u32 }
-            }
-        }
-
-        impl R {
-            #[inline]
-            pub fn bits(&self) -> u32 {
-                self.bits
-            }
-        }
-    )
-}
-
-macro_rules! w {
-    ($MOD:ident, $TYPE:ident, $CSR:expr) => (
-        macro_rules! func {
-            ($fnname:ident, $csrop:ident) => (
-                #[inline(always)]
-                pub fn $fnname<F>(&self, f: F)
-                    where
-                    F: FnOnce(&mut W) -> &mut W,
-                {
-                    let mut w = W { bits: 0 };
-                    f(&mut w);
-                    csr_asm!($csrop, $CSR, w.bits as usize);
-                }
-            )
-        }
-
-        pub struct W {
-            bits: u32,
-        }
-
-        impl super::$TYPE {
-            func!(write, csrrw);
-            func!(set, csrrs);
-            func!(clear, csrrc);
-        }
-
-        impl W {
-            #[inline]
-            pub fn bits(&mut self, value: u32) -> &mut W {
-                self.bits = value;
-                self
-            }
-            #[inline]
-            pub fn set_bits(&mut self, value: u32) -> &mut W {
-                self.bits |= value;
-                self
-            }
-            #[inline]
-            pub fn clear_bits(&mut self, value: u32) -> &mut W {
-                self.bits &= !value;
-                self
-            }
-        }
-    )
-}
-
-macro_rules! rw {
-    ($MOD:ident, $TYPE:ident, $CSR:expr) => (
-        r!($MOD, $TYPE, $CSR);
-        w!($MOD, $TYPE, $CSR);
-    )
-}
-
-macro_rules! csr {
-    ($MOD:ident, $TYPE:ident, $CSR:expr, $MACRO:ident) => (
-        pub struct $TYPE {}
-        #[allow(non_upper_case_globals)]
-        pub const $MOD: $TYPE = $TYPE {};
-
-        pub mod $MOD {
-            $MACRO!($MOD, $TYPE, $CSR);
-        }
-    )
-}
-
-/// User Trap Setup
-csr!(ustatus, USTATUS, 0x000, rw);
-csr!(uie, UIE, 0x004, rw);
-csr!(utvec, UTVEC, 0x005, rw);
-/// User Trap Handling
-csr!(uscratch, USCRATCH, 0x040, rw);
-csr!(uepc, UEPC, 0x041, rw);
-csr!(ucause, UCAUSE, 0x042, rw);
-csr!(utval, UTVAL, 0x043, rw);
-csr!(uip, UIP, 0x044, r);
-/// User Floating-Point CSRs
-csr!(fflags, FFLAGS, 0x001, rw);
-csr!(frm, FRM, 0x002, rw);
-csr!(fcsr, FCSR, 0x003, rw);
-/// User Counter/Timers
-csr!(cycle, CYCLE, 0xC00, rw);
-csr!(time, TIME, 0xC01, rw);
-csr!(instret, INSTRET, 0xC02, rw);
-// TODO: hpmcounter3 - hpmcounter31
-csr!(cycleh, CYCLEH, 0xC80, rw);
-csr!(timeh, TIMEH, 0xC81, rw);
-csr!(instreth, INSTRETH, 0xC82, rw);
-// TODO: hpmcounter3h - hpmcounter31h
-
-/// Supervisor Trap Setup
-csr!(sstatus, SSTATUS, 0x100, rw);
-csr!(sedeleg, SEDELEG, 0x102, rw);
-csr!(sideleg, SIDELEG, 0x103, rw);
-csr!(sie, SIE, 0x104, rw);
-csr!(stvec, STVEC, 0x105, rw);
-csr!(scounteren, SCOUNTEREN, 0x106, rw);
-/// Supervisor Trap Handling
-csr!(sscratch, SSCRATCH, 0x140, rw);
-csr!(sepc, SEPC, 0x141, rw);
-csr!(scause, SCAUSE, 0x142, rw);
-csr!(stval, STVAL, 0x143, rw);
-csr!(sip, SIP, 0x144, r);
-/// Supervisor Protection and Translation
-csr!(satp, SATP, 0x180, rw);
-
-/// Machine Information Registers
-csr!(mvendorid, MVENDORID, 0xF11, r);
-csr!(marchid, MARCHID, 0xF12, r);
-csr!(mimpid, MIMPID, 0xF13, r);
-csr!(mhartid, MHARTID, 0xF14, r);
-/// Machine Trap Setup
-csr!(mstatus, MSTATUS, 0x300, rw);
-csr!(misa, MISA, 0x301, r);
-csr!(medeleg, MEDELEG, 0x302, rw);
-csr!(mideleg, MIDELEG, 0x303, rw);
-csr!(mie, MIE, 0x304, rw);
-csr!(mtvec, MTVEC, 0x305, rw);
-csr!(mcounteren, MCOUNTEREN, 0x306, rw);
-/// Machine Trap Handling
-csr!(mscratch, MSCRATCH, 0x340, rw);
-csr!(mepc, MEPC, 0x341, rw);
-csr!(mcause, MCAUSE, 0x342, r);
-csr!(mtval, MTVAL, 0x343, rw);
-csr!(mip, MIP, 0x344, r);
-/// Machine Protection and Translation
-csr!(pmpcfg0, PMPCFG0, 0x3A0, rw);
-csr!(pmpcfg1, PMPCFG1, 0x3A1, rw);
-csr!(pmpcfg2, PMPCFG2, 0x3A2, rw);
-csr!(pmpcfg3, PMPCFG3, 0x3A3, rw);
-// TODO pmpaddr0 - pmpaddr15
-
-/// Machine Counter/Timers
-csr!(mcycle, MCYCLE, 0xB00, rw);
-csr!(minstret, MINSTRET, 0xB02, rw);
-// TODO mhpmcounter3 .. mhpmcounter31
-csr!(mcycleh, MCYCLEH, 0xB80, rw);
-csr!(minstreth, MINSTRETH, 0xB82, rw);
-// TODO mhpmcounter3h .. mhpmcounter31h
-/// Machine Counter Setup
-// TODO mhpmevent3 .. mhpmevent31
-
-/// Debug/Trace Registers (shared with Debug Mode)
-csr!(tselect, TSELECT, 0x7A0, rw);
-csr!(tdata1, TDATA1, 0x7A1, rw);
-csr!(tdata2, TDATA2, 0x7A2, rw);
-csr!(tdata3, TDATA3, 0x7A3, rw);
-/// Debug Mode Registers
-csr!(dcsr, DCSR, 0x7B0, rw);
-csr!(dpc, DPC, 0x7B1, rw);
-csr!(dscratch, DSCRATCH, 0x7B2, rw);
-
-/// Machine Cause CSR (mcause) is ReadOnly.
-/// Trap Cause
-#[derive(Copy, Clone, Debug)]
-pub enum Trap {
-    Interrupt(Interrupt),
-    Exception(Exception),
-}
-
-/// Interrupt
-#[derive(Copy, Clone, Debug)]
-pub enum Interrupt {
-    UserSoft,
-    SupervisorSoft,
-    MachineSoft,
-    UserTimer,
-    SupervisorTimer,
-    MachineTimer,
-    UserExternal,
-    SupervisorExternal,
-    MachineExternal,
-}
-
-impl Interrupt {
-    pub fn from(nr: u32) -> Self {
-        match nr {
-            0 => Interrupt::UserSoft,
-            1 => Interrupt::SupervisorSoft,
-            3 => Interrupt::MachineSoft,
-            4 => Interrupt::UserTimer,
-            5 => Interrupt::SupervisorTimer,
-            7 => Interrupt::MachineTimer,
-            8 => Interrupt::UserExternal,
-            9 => Interrupt::SupervisorExternal,
-            11 => Interrupt::MachineExternal,
-            _ => unreachable!()
-        }
-    }
-}
-
-/// Exception
-#[derive(Copy, Clone, Debug)]
-pub enum Exception {
-    InstructionMisaligned,
-    InstructionFault,
-    IllegalInstruction,
-    Breakpoint,
-    LoadMisaligned,
-    LoadFault,
-    StoreMisaligned,
-    StoreFault,
-    UserEnvCall,
-    SupervisorEnvCall,
-    MachineEnvCall,
-    InstructionPageFault,
-    LoadPageFault,
-    StorePageFault,
-}
-
-impl Exception {
-    pub fn from(nr: u32) -> Self {
-        match nr {
-            0 => Exception::InstructionMisaligned,
-            1 => Exception::InstructionFault,
-            2 => Exception::IllegalInstruction,
-            3 => Exception::Breakpoint,
-            4 => Exception::LoadMisaligned,
-            5 => Exception::LoadFault,
-            6 => Exception::StoreMisaligned,
-            7 => Exception::StoreFault,
-            8 => Exception::UserEnvCall,
-            9 => Exception::SupervisorEnvCall,
-            11 => Exception::MachineEnvCall,
-            12 => Exception::InstructionPageFault,
-            13 => Exception::LoadPageFault,
-            15 => Exception::StorePageFault,
-            _ => unreachable!()
-        }
-    }
-}
-
-
-impl mcause::R {
-    #[inline]
-    /// Trap Cause
-    pub fn cause(&self) -> Trap {
-        let bits = self.bits();
-        let code = bits & !(1 << 31);
-        match bits & (1 << 31) == 1 << 31 {
-            true => Trap::Interrupt(Interrupt::from(code)),
-            false => Trap::Exception(Exception::from(code)),
-        }
-    }
-
-    #[inline]
-    /// Is trap cause an interrupt.
-    pub fn is_interrupt(&self) -> bool {
-        match self.cause() {
-            Trap::Interrupt(_) => true,
-            _ => false,
-        }
-    }
-
-    #[inline]
-    /// Is trap cause an exception.
-    pub fn is_exception(&self) -> bool {
-        match self.cause() {
-            Trap::Exception(_) => true,
-            _ => false,
-        }
-    }
-}
-
-/// Machine Status CSR is ReadWrite
-// TODO: Virtualization, Memory Privilege and Extension Context Fields
-
-/// Machine Previous Privilege Mode
-pub enum MPP {
-    Machine = 3,
-    Supervisor = 1,
-    User = 0,
-}
-
-/// Supervisor Previous Privilege Mode
-pub enum SPP {
-    Supervisor = 1,
-    User = 0,
-}
-
-
-impl mstatus::R {
-    #[inline]
-    /// User Interrupt Enable
-    pub fn uie(&self) -> bool {
-        self.bits() & (1 << 0) == 1 << 0
-    }
-
-    #[inline]
-    /// Supervisor Interrupt Enable
-    pub fn sie(&self) -> bool {
-        self.bits() & (1 << 1) == 1 << 1
-    }
-
-    #[inline]
-    /// Machine Interrupt Enable
-    pub fn mie(&self) -> bool {
-        self.bits() & (1 << 3) == 1 << 3
-    }
-
-    #[inline]
-    /// User Previous Interrupt Enable
-    pub fn upie(&self) -> bool {
-        self.bits() & (1 << 4) == 1 << 4
-    }
-
-    #[inline]
-    /// Supervisor Previous Interrupt Enable
-    pub fn spie(&self) -> bool {
-        self.bits() & (1 << 5) == 1 << 5
-    }
-
-    #[inline]
-    /// User Previous Interrupt Enable
-    pub fn mpie(&self) -> bool {
-        self.bits() & (1 << 7) == 1 << 7
-    }
-
-    #[inline]
-    /// Supervisor Previous Privilege Mode
-    pub fn spp(&self) -> SPP {
-        match self.bits() & (1 << 8) == (1 << 8) {
-            true => SPP::Supervisor,
-            false => SPP::User,
-        }
-    }
-
-    #[inline]
-    /// Machine Previous Privilege Mode
-    pub fn mpp(&self) -> MPP {
-        match (self.bits() & (0b11 << 11)) >> 11 {
-            0b00 => MPP::User,
-            0b01 => MPP::Supervisor,
-            0b11 => MPP::Machine,
-            _ => unreachable!(),
-        }
-    }
-}
-
-impl mstatus::W {
-    #[inline]
-    /// User Interrupt Enable
-    pub fn uie(&mut self) -> &mut mstatus::W {
-        self.set_bits(1 << 0)
-    }
-
-    #[inline]
-    /// Supervisor Interrupt Enable
-    pub fn sie(&mut self) -> &mut mstatus::W {
-        self.set_bits(1 << 1)
-    }
-
-    #[inline]
-    /// Machine Interrupt Enable
-    pub fn mie(&mut self) -> &mut mstatus::W {
-        self.set_bits(1 << 3)
-    }
-
-    #[inline]
-    /// User Previous Interrupt Enable
-    pub fn upie(&mut self) -> &mut mstatus::W {
-        self.set_bits(1 << 4)
-    }
-
-    #[inline]
-    /// User Previous Interrupt Enable
-    pub fn spie(&mut self) -> &mut mstatus::W {
-        self.set_bits(1 << 5)
-    }
-
-    #[inline]
-    /// User Previous Interrupt Enable
-    pub fn mpie(&mut self) -> &mut mstatus::W {
-        self.set_bits(1 << 7)
-    }
-
-    #[inline]
-    /// Supervisor Previous Privilege Mode
-    pub fn spp(&mut self, value: SPP) -> &mut mstatus::W {
-        self.set_bits((value as u32) << 8)
-    }
-
-    #[inline]
-    /// Machine Previous Privilege Mode
-    pub fn mpp(&mut self, value: MPP) -> &mut mstatus::W {
-        self.set_bits((value as u32) << 11)
-    }
-}
-
-/// Machine Interrupt Enable CSR (mie) is ReadWrite.
-impl mie::R {
-    #[inline]
-    /// User Software Interrupt Enable
-    pub fn usoft(&self) -> bool {
-        self.bits() & (1 << 0) == 1 << 0
-    }
-
-    #[inline]
-    /// Supervisor Software Interrupt Enable
-    pub fn ssoft(&self) -> bool {
-        self.bits() & (1 << 1) == 1 << 1
-    }
-
-    #[inline]
-    /// Machine Software Interrupt Enable
-    pub fn msoft(&self) -> bool {
-        self.bits() & (1 << 3) == 1 << 3
-    }
-
-    #[inline]
-    /// User Timer Interrupt Enable
-    pub fn utimer(&self) -> bool {
-        self.bits() & (1 << 4) == 1 << 4
-    }
-
-    #[inline]
-    /// Supervisor Timer Interrupt Enable
-    pub fn stimer(&self) -> bool {
-        self.bits() & (1 << 5) == 1 << 5
-    }
-
-    #[inline]
-    /// Machine Timer Interrupt Enable
-    pub fn mtimer(&self) -> bool {
-        self.bits() & (1 << 7) == 1 << 7
-    }
-
-    #[inline]
-    /// User External Interrupt Enable
-    pub fn uext(&self) -> bool {
-        self.bits() & (1 << 8) == 1 << 8
-    }
-
-    #[inline]
-    /// Supervisor External Interrupt Enable
-    pub fn sext(&self) -> bool {
-        self.bits() & (1 << 9) == 1 << 9
-    }
-
-    #[inline]
-    /// Machine External Interrupt Enable
-    pub fn mext(&self) -> bool {
-        self.bits() & (1 << 11) == 1 << 11
-    }
-}
-
-impl mie::W {
-    #[inline]
-    /// User Software Interrupt Enable
-    pub fn usoft(&mut self) -> &mut mie::W {
-        self.set_bits(1 << 0)
-    }
-
-    #[inline]
-    /// Supervisor Software Interrupt Enable
-    pub fn ssoft(&mut self) -> &mut mie::W {
-        self.set_bits(1 << 1)
-    }
-
-    #[inline]
-    /// Machine Software Interrupt Enable
-    pub fn msoft(&mut self) -> &mut mie::W {
-        self.set_bits(1 << 3)
-    }
-
-    #[inline]
-    /// User Timer Interrupt Enable
-    pub fn utimer(&mut self) -> &mut mie::W {
-        self.set_bits(1 << 4)
-    }
-
-    #[inline]
-    /// Supervisor Timer Interrupt Enable
-    pub fn stimer(&mut self) -> &mut mie::W {
-        self.set_bits(1 << 5)
-    }
-
-    #[inline]
-    /// Machine Timer Interrupt Enable
-    pub fn mtimer(&mut self) -> &mut mie::W {
-        self.set_bits(1 << 7)
-    }
-
-    #[inline]
-    /// User External Interrupt Enable
-    pub fn uext(&mut self) -> &mut mie::W {
-        self.set_bits(1 << 8)
-    }
-
-    #[inline]
-    /// Supervisor External Interrupt Enable
-    pub fn sext(&mut self) -> &mut mie::W {
-        self.set_bits(1 << 9)
-    }
-
-    #[inline]
-    /// Machine External Interrupt Enable
-    pub fn mext(&mut self) -> &mut mie::W {
-        self.set_bits(1 << 11)
-    }
-}
-
-/// Machine Interrupt Pending CSR (mip) is ReadOnly.
-impl mip::R {
-    #[inline]
-    /// User Software Interrupt Enable
-    pub fn usoft(&self) -> bool {
-        self.bits() & (1 << 0) == 1 << 0
-    }
-
-    #[inline]
-    /// Supervisor Software Interrupt Enable
-    pub fn ssoft(&self) -> bool {
-        self.bits() & (1 << 1) == 1 << 1
-    }
-
-    #[inline]
-    /// Machine Software Interrupt Enable
-    pub fn msoft(&self) -> bool {
-        self.bits() & (1 << 3) == 1 << 3
-    }
-
-    #[inline]
-    /// User Timer Interrupt Enable
-    pub fn utimer(&self) -> bool {
-        self.bits() & (1 << 4) == 1 << 4
-    }
-
-    #[inline]
-    /// Supervisor Timer Interrupt Enable
-    pub fn stimer(&self) -> bool {
-        self.bits() & (1 << 5) == 1 << 5
-    }
-
-    #[inline]
-    /// Machine Timer Interrupt Enable
-    pub fn mtimer(&self) -> bool {
-        self.bits() & (1 << 7) == 1 << 7
-    }
-
-    #[inline]
-    /// User External Interrupt Enable
-    pub fn uext(&self) -> bool {
-        self.bits() & (1 << 8) == 1 << 8
-    }
-
-    #[inline]
-    /// Supervisor External Interrupt Enable
-    pub fn sext(&self) -> bool {
-        self.bits() & (1 << 9) == 1 << 9
-    }
-
-    #[inline]
-    /// Machine External Interrupt Enable
-    pub fn mext(&self) -> bool {
-        self.bits() & (1 << 11) == 1 << 11
-    }
-}
diff --git a/src/interrupt.rs b/src/interrupt.rs
index d3adae2..edb2be9 100644
--- a/src/interrupt.rs
+++ b/src/interrupt.rs
@@ -2,13 +2,14 @@
 
 // NOTE: Adapted from cortex-m/src/interrupt.rs
 pub use bare_metal::{CriticalSection, Mutex, Nr};
+use register::mstatus;
 
 /// Disables all interrupts
 #[inline]
-pub fn disable() {
+pub unsafe fn disable() {
     match () {
         #[cfg(target_arch = "riscv")]
-        () => ::csr::mstatus.clear(|w| w.mie()),
+        () => mstatus::clear_mie(),
         #[cfg(not(target_arch = "riscv"))]
         () => {}
     }
@@ -23,7 +24,7 @@ pub fn disable() {
 pub unsafe fn enable() {
     match () {
         #[cfg(target_arch = "riscv")]
-        () => ::csr::mstatus.set(|w| w.mie()),
+        () => mstatus::set_mie(),
         #[cfg(not(target_arch = "riscv"))]
         () => {}
     }
@@ -36,17 +37,17 @@ pub fn free<F, R>(f: F) -> R
 where
     F: FnOnce(&CriticalSection) -> R,
 {
-    let mstatus = ::csr::mstatus.read();
+    let mstatus = mstatus::read();
 
     // disable interrupts
-    disable();
+    unsafe { disable(); }
 
     let r = f(unsafe { &CriticalSection::new() });
 
     // If the interrupts were active before our `disable` call, then re-enable
     // them. Otherwise, keep them disabled
     if mstatus.mie() {
-        unsafe { enable() }
+        unsafe { enable(); }
     }
 
     r
diff --git a/src/lib.rs b/src/lib.rs
index fa10060..c0f93d5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,5 +14,5 @@
 extern crate bare_metal;
 
 pub mod asm;
-pub mod csr;
 pub mod interrupt;
+pub mod register;
diff --git a/src/register/mcause.rs b/src/register/mcause.rs
new file mode 100644
index 0000000..fef8530
--- /dev/null
+++ b/src/register/mcause.rs
@@ -0,0 +1,154 @@
+//! mcause register
+
+/// mcause register
+#[derive(Clone, Copy, Debug)]
+pub struct Mcause {
+    bits: usize,
+}
+
+/// Trap Cause
+#[derive(Copy, Clone, Debug)]
+pub enum Trap {
+    Interrupt(Interrupt),
+    Exception(Exception),
+}
+
+/// Interrupt
+#[derive(Copy, Clone, Debug)]
+pub enum Interrupt {
+    UserSoft,
+    SupervisorSoft,
+    MachineSoft,
+    UserTimer,
+    SupervisorTimer,
+    MachineTimer,
+    UserExternal,
+    SupervisorExternal,
+    MachineExternal,
+    Unknown,
+}
+
+/// Exception
+#[derive(Copy, Clone, Debug)]
+pub enum Exception {
+    InstructionMisaligned,
+    InstructionFault,
+    IllegalInstruction,
+    Breakpoint,
+    LoadMisaligned,
+    LoadFault,
+    StoreMisaligned,
+    StoreFault,
+    UserEnvCall,
+    SupervisorEnvCall,
+    MachineEnvCall,
+    InstructionPageFault,
+    LoadPageFault,
+    StorePageFault,
+    Unknown,
+}
+
+impl Interrupt {
+    pub fn from(nr: usize) -> Self {
+        match nr {
+            0 => Interrupt::UserSoft,
+            1 => Interrupt::SupervisorSoft,
+            3 => Interrupt::MachineSoft,
+            4 => Interrupt::UserTimer,
+            5 => Interrupt::SupervisorTimer,
+            7 => Interrupt::MachineTimer,
+            8 => Interrupt::UserExternal,
+            9 => Interrupt::SupervisorExternal,
+            11 => Interrupt::MachineExternal,
+            _ => Interrupt::Unknown,
+        }
+    }
+}
+
+
+impl Exception {
+    pub fn from(nr: usize) -> Self {
+        match nr {
+            0 => Exception::InstructionMisaligned,
+            1 => Exception::InstructionFault,
+            2 => Exception::IllegalInstruction,
+            3 => Exception::Breakpoint,
+            4 => Exception::LoadMisaligned,
+            5 => Exception::LoadFault,
+            6 => Exception::StoreMisaligned,
+            7 => Exception::StoreFault,
+            8 => Exception::UserEnvCall,
+            9 => Exception::SupervisorEnvCall,
+            11 => Exception::MachineEnvCall,
+            12 => Exception::InstructionPageFault,
+            13 => Exception::LoadPageFault,
+            15 => Exception::StorePageFault,
+            _ => Exception::Unknown,
+        }
+    }
+}
+impl Mcause {
+    /// Returns the contents of the register as raw bits
+    #[inline]
+    pub fn bits(&self) -> usize {
+        self.bits
+    }
+
+    /// Returns the code field
+    pub fn code(&self) -> usize {
+        match () {
+            #[cfg(target_pointer_width = "32")]
+            () => self.bits & !(1 << 31),
+            #[cfg(target_pointer_width = "64")]
+            () => self.bits & !(1 << 63),
+            #[cfg(target_pointer_width = "128")]
+            () => self.bits & !(1 << 127),
+        }
+    }
+
+    /// Trap Cause
+    #[inline]
+    pub fn cause(&self) -> Trap {
+        if self.is_interrupt() {
+            Trap::Interrupt(Interrupt::from(self.code()))
+        } else {
+            Trap::Exception(Exception::from(self.code()))
+        }
+    }
+
+    /// Is trap cause an interrupt.
+    #[inline]
+    pub fn is_interrupt(&self) -> bool {
+        match () {
+            #[cfg(target_pointer_width = "32")]
+            () => self.bits & (1 << 31) == 1 << 31,
+            #[cfg(target_pointer_width = "64")]
+            () => self.bits & (1 << 63) == 1 << 63,
+            #[cfg(target_pointer_width = "128")]
+            () => self.bits & (1 << 127) == 1 << 127,
+        }
+    }
+
+    /// Is trap cause an exception.
+    #[inline]
+    pub fn is_exception(&self) -> bool {
+        !self.is_interrupt()
+    }
+}
+
+/// Reads the CSR
+#[inline]
+pub fn read() -> Mcause {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => {
+            let r: usize;
+            unsafe {
+                asm!("csrrs $0, 0x342, x0" : "=r"(r) ::: "volatile");
+            }
+            Mcause { bits: r }
+        }
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
diff --git a/src/register/mcycle.rs b/src/register/mcycle.rs
new file mode 100644
index 0000000..d98da32
--- /dev/null
+++ b/src/register/mcycle.rs
@@ -0,0 +1,18 @@
+//! mcycle register
+
+/// Reads the CSR
+#[inline]
+pub fn read() -> usize {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => {
+            let r: usize;
+            unsafe {
+                asm!("csrrs $0, 0xB00, x0" : "=r"(r) ::: "volatile");
+            }
+            r
+        }
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
diff --git a/src/register/mcycleh.rs b/src/register/mcycleh.rs
new file mode 100644
index 0000000..e03f6e5
--- /dev/null
+++ b/src/register/mcycleh.rs
@@ -0,0 +1,18 @@
+//! mcycleh register
+
+/// Reads the CSR
+#[inline]
+pub fn read() -> usize {
+    match () {
+        #[cfg(all(target_arch = "riscv", target_pointer_width = "32"))]
+        () => {
+            let r: usize;
+            unsafe {
+                asm!("csrrs $0, 0xB80, x0" : "=r"(r) ::: "volatile");
+            }
+            r
+        }
+        #[cfg(any(not(target_arch = "riscv"), not(target_pointer_width = "32")))]
+        () => unimplemented!(),
+    }
+}
diff --git a/src/register/mie.rs b/src/register/mie.rs
new file mode 100644
index 0000000..d572976
--- /dev/null
+++ b/src/register/mie.rs
@@ -0,0 +1,154 @@
+//! mie register
+
+/// mie register
+#[derive(Clone, Copy, Debug)]
+pub struct Mie {
+    bits: usize,
+}
+
+impl Mie {
+    /// Returns the contents of the register as raw bits
+    #[inline]
+    pub fn bits(&self) -> usize {
+        self.bits
+    }
+
+    /// User Software Interrupt Enable
+    #[inline]
+    pub fn usoft(&self) -> bool {
+        self.bits & (1 << 0) == 1 << 0
+    }
+
+    /// Supervisor Software Interrupt Enable
+    #[inline]
+    pub fn ssoft(&self) -> bool {
+        self.bits & (1 << 1) == 1 << 1
+    }
+
+    /// Machine Software Interrupt Enable
+    #[inline]
+    pub fn msoft(&self) -> bool {
+        self.bits & (1 << 3) == 1 << 3
+    }
+
+    /// User Timer Interrupt Enable
+    #[inline]
+    pub fn utimer(&self) -> bool {
+        self.bits & (1 << 4) == 1 << 4
+    }
+
+    /// Supervisor Timer Interrupt Enable
+    #[inline]
+    pub fn stimer(&self) -> bool {
+        self.bits & (1 << 5) == 1 << 5
+    }
+
+    /// Machine Timer Interrupt Enable
+    #[inline]
+    pub fn mtimer(&self) -> bool {
+        self.bits & (1 << 7) == 1 << 7
+    }
+
+    /// User External Interrupt Enable
+    #[inline]
+    pub fn uext(&self) -> bool {
+        self.bits & (1 << 8) == 1 << 8
+    }
+
+    /// Supervisor External Interrupt Enable
+    #[inline]
+    pub fn sext(&self) -> bool {
+        self.bits & (1 << 9) == 1 << 9
+    }
+
+    /// Machine External Interrupt Enable
+    #[inline]
+    pub fn mext(&self) -> bool {
+        self.bits & (1 << 11) == 1 << 11
+    }
+}
+
+/// Reads the CSR
+#[inline]
+pub fn read() -> Mie {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => {
+            let r: usize;
+            unsafe {
+                asm!("csrrs $0, 0x304, x0" : "=r"(r) ::: "volatile");
+            }
+            Mie { bits: r }
+        }
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
+
+/// Sets the CSR
+#[cfg_attr(not(target_arch = "riscv"), allow(unused_variables))]
+#[inline]
+unsafe fn set(bits: usize) {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => asm!("csrrs x0, 0x304, $0" :: "r"(bits) :: "volatile"),
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
+
+/// Clears the CSR
+#[cfg_attr(not(target_arch = "riscv"), allow(unused_variables))]
+#[inline]
+unsafe fn clear(bits: usize) {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => asm!("csrrc x0, 0x304, $0" :: "r"(bits) :: "volatile"),
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
+
+macro_rules! set_csr {
+    ($set_field:ident, $e:expr) => {
+        #[inline]
+        pub unsafe fn $set_field() {
+            set($e);
+        }
+    }
+}
+
+macro_rules! clear_csr {
+    ($clear_field:ident, $e:expr) => {
+        #[inline]
+        pub unsafe fn $clear_field() {
+            clear($e);
+        }
+    }
+}
+
+macro_rules! set_clear_csr {
+    ($set_field:ident, $clear_field:ident, $e:expr) => {
+        set_csr!($set_field, $e);
+        clear_csr!($clear_field, $e);
+    }
+}
+
+/// User Software Interrupt Enable
+set_clear_csr!(set_usoft, clear_usoft, 1 << 0);
+/// Supervisor Software Interrupt Enable
+set_clear_csr!(set_ssoft, clear_ssoft, 1 << 1);
+/// Machine Software Interrupt Enable
+set_clear_csr!(set_msoft, clear_msoft, 1 << 3);
+/// User Timer Interrupt Enable
+set_clear_csr!(set_utimer, clear_utimer, 1 << 4);
+/// Supervisor Timer Interrupt Enable
+set_clear_csr!(set_stimer, clear_stimer, 1 << 5);
+/// Machine Timer Interrupt Enable
+set_clear_csr!(set_mtimer, clear_mtimer, 1 << 7);
+/// User External Interrupt Enable
+set_clear_csr!(set_uext, clear_uext, 1 << 8);
+/// Supervisor External Interrupt Enable
+set_clear_csr!(set_sext, clear_sext, 1 << 9);
+/// Machine External Interrupt Enable
+set_clear_csr!(set_mext, clear_mext, 1 << 11);
diff --git a/src/register/minstret.rs b/src/register/minstret.rs
new file mode 100644
index 0000000..3576800
--- /dev/null
+++ b/src/register/minstret.rs
@@ -0,0 +1,18 @@
+//! minstret register
+
+/// Reads the CSR
+#[inline]
+pub fn read() -> usize {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => {
+            let r: usize;
+            unsafe {
+                asm!("csrrs $0, 0xB02, x0" : "=r"(r) ::: "volatile");
+            }
+            r
+        }
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
diff --git a/src/register/minstreth.rs b/src/register/minstreth.rs
new file mode 100644
index 0000000..8ec4afa
--- /dev/null
+++ b/src/register/minstreth.rs
@@ -0,0 +1,18 @@
+//! minstreth register
+
+/// Reads the CSR
+#[inline]
+pub fn read() -> usize {
+    match () {
+        #[cfg(all(target_arch = "riscv", target_pointer_width = "32"))]
+        () => {
+            let r: usize;
+            unsafe {
+                asm!("csrrs $0, 0xB82, x0" : "=r"(r) ::: "volatile");
+            }
+            r
+        },
+        #[cfg(any(not(target_arch = "riscv"), not(target_pointer_width = "32")))]
+        () => unimplemented!(),
+    }
+}
diff --git a/src/register/mip.rs b/src/register/mip.rs
new file mode 100644
index 0000000..09eb10a
--- /dev/null
+++ b/src/register/mip.rs
@@ -0,0 +1,86 @@
+//! mip register
+
+/// mip register
+#[derive(Clone, Copy, Debug)]
+pub struct Mip {
+    bits: usize,
+}
+
+impl Mip {
+    /// Returns the contents of the register as raw bits
+    #[inline]
+    pub fn bits(&self) -> usize {
+        self.bits
+    }
+
+    /// User Software Interrupt Pending
+    #[inline]
+    pub fn usoft(&self) -> bool {
+        self.bits & (1 << 0) == 1 << 0
+    }
+
+    /// Supervisor Software Interrupt Pending
+    #[inline]
+    pub fn ssoft(&self) -> bool {
+        self.bits & (1 << 1) == 1 << 1
+    }
+
+    /// Machine Software Interrupt Pending
+    #[inline]
+    pub fn msoft(&self) -> bool {
+        self.bits & (1 << 3) == 1 << 3
+    }
+
+    /// User Timer Interrupt Pending
+    #[inline]
+    pub fn utimer(&self) -> bool {
+        self.bits & (1 << 4) == 1 << 4
+    }
+
+    /// Supervisor Timer Interrupt Pending
+    #[inline]
+    pub fn stimer(&self) -> bool {
+        self.bits & (1 << 5) == 1 << 5
+    }
+
+    /// Machine Timer Interrupt Pending
+    #[inline]
+    pub fn mtimer(&self) -> bool {
+        self.bits & (1 << 7) == 1 << 7
+    }
+
+    /// User External Interrupt Pending
+    #[inline]
+    pub fn uext(&self) -> bool {
+        self.bits & (1 << 8) == 1 << 8
+    }
+
+    /// Supervisor External Interrupt Pending
+    #[inline]
+    pub fn sext(&self) -> bool {
+        self.bits & (1 << 9) == 1 << 9
+    }
+
+    /// Machine External Interrupt Pending
+    #[inline]
+    pub fn mext(&self) -> bool {
+        self.bits & (1 << 11) == 1 << 11
+    }
+}
+
+/// Reads the CSR
+#[inline]
+pub fn read() -> Mip {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => {
+            let r: usize;
+            unsafe {
+                asm!("csrrs $0, 0x344, x0" : "=r"(r) ::: "volatile");
+            }
+            Mip { bits: r }
+        }
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
diff --git a/src/register/misa.rs b/src/register/misa.rs
new file mode 100644
index 0000000..eb3f246
--- /dev/null
+++ b/src/register/misa.rs
@@ -0,0 +1,69 @@
+//! misa register
+
+/// misa register
+#[derive(Clone, Copy, Debug)]
+pub struct Misa {
+    bits: usize,
+}
+
+/// Machine XLEN
+pub enum MXL {
+    XLEN32,
+    XLEN64,
+    XLEN128,
+}
+
+impl Misa {
+    /// Returns the contents of the register as raw bits
+    pub fn bits(&self) -> usize {
+        self.bits
+    }
+
+    /// Returns the machine xlen.
+    pub fn mxl(&self) -> MXL {
+        let value = match () {
+            #[cfg(target_pointer_width = "32")]
+            () => (self.bits >> 30) as u8,
+            #[cfg(target_pointer_widht = "64")]
+            () => (self.bits >> 62) as u8,
+        };
+        match value {
+            1 => MXL::XLEN32,
+            2 => MXL::XLEN64,
+            3 => MXL::XLEN128,
+            _ => unreachable!(),
+        }
+    }
+
+    /// Returns true when the atomic extension is implemented.
+    pub fn has_extension(&self, extension: char) -> bool {
+        let bit = extension as u8 - 65;
+        if bit > 25 {
+            return false;
+        }
+        self.bits & (1 >> bit) == (1 >> bit)
+    }
+}
+
+/// Reads the CSR
+#[inline]
+pub fn read() -> Option<Misa> {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => {
+            let r: usize;
+            unsafe {
+                asm!("csrrs $0, 0x301, x0" : "=r"(r) ::: "volatile");
+            }
+            // When misa is hardwired to zero it means that the misa csr
+            // isn't implemented.
+            if r == 0 {
+                None
+            } else {
+                Some(Misa { bits: r })
+            }
+        },
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
diff --git a/src/register/mod.rs b/src/register/mod.rs
new file mode 100644
index 0000000..df94575
--- /dev/null
+++ b/src/register/mod.rs
@@ -0,0 +1,23 @@
+//! RISCV CSR's
+//!
+//! The following registers are not available on 64-bit implementations.
+//!
+//! - cycleh
+//! - timeh
+//! - instreth
+//! - hpmcounter[3-31]h
+//! - mcycleh
+//! - minstreth
+//! - mhpmcounter[3-31]h
+
+pub mod mcause;
+pub mod mcycle;
+pub mod mcycleh;
+pub mod mie;
+pub mod mip;
+pub mod minstret;
+pub mod minstreth;
+pub mod misa;
+pub mod mstatus;
+pub mod mtvec;
+pub mod mvendorid;
diff --git a/src/register/mstatus.rs b/src/register/mstatus.rs
new file mode 100644
index 0000000..b49bebb
--- /dev/null
+++ b/src/register/mstatus.rs
@@ -0,0 +1,169 @@
+//! mstatus register
+// TODO: Virtualization, Memory Privilege and Extension Context Fields
+
+/// mstatus register
+#[derive(Clone, Copy, Debug)]
+pub struct Mstatus {
+    bits: usize,
+}
+
+/// Machine Previous Privilege Mode
+pub enum MPP {
+    Machine = 3,
+    Supervisor = 1,
+    User = 0,
+}
+
+/// Supervisor Previous Privilege Mode
+pub enum SPP {
+    Supervisor = 1,
+    User = 0,
+}
+
+impl Mstatus {
+    /// User Interrupt Enable
+    #[inline]
+    pub fn uie(&self) -> bool {
+        self.bits & (1 << 0) == 1 << 0
+    }
+
+    /// Supervisor Interrupt Enable
+    #[inline]
+    pub fn sie(&self) -> bool {
+        self.bits & (1 << 1) == 1 << 1
+    }
+
+    /// Machine Interrupt Enable
+    #[inline]
+    pub fn mie(&self) -> bool {
+        self.bits & (1 << 3) == 1 << 3
+    }
+
+    /// User Previous Interrupt Enable
+    #[inline]
+    pub fn upie(&self) -> bool {
+        self.bits & (1 << 4) == 1 << 4
+    }
+
+    /// Supervisor Previous Interrupt Enable
+    #[inline]
+    pub fn spie(&self) -> bool {
+        self.bits & (1 << 5) == 1 << 5
+    }
+
+    /// User Previous Interrupt Enable
+    #[inline]
+    pub fn mpie(&self) -> bool {
+        self.bits & (1 << 7) == 1 << 7
+    }
+
+    /// Supervisor Previous Privilege Mode
+    #[inline]
+    pub fn spp(&self) -> SPP {
+        match self.bits & (1 << 8) == (1 << 8) {
+            true => SPP::Supervisor,
+            false => SPP::User,
+        }
+    }
+
+    /// Machine Previous Privilege Mode
+    #[inline]
+    pub fn mpp(&self) -> MPP {
+        match (self.bits & (0b11 << 11)) >> 11 {
+            0b00 => MPP::User,
+            0b01 => MPP::Supervisor,
+            0b11 => MPP::Machine,
+            _ => unreachable!(),
+        }
+    }
+}
+
+
+/// Reads the CSR
+#[inline]
+pub fn read() -> Mstatus {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => {
+            let r: usize;
+            unsafe {
+                asm!("csrrs $0, 0x300, x0" : "=r"(r) ::: "volatile");
+            }
+            Mstatus { bits: r }
+        }
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
+
+/// Sets the CSR
+#[cfg_attr(not(target_arch = "riscv"), allow(unused_variables))]
+#[inline]
+unsafe fn set(bits: usize) {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => asm!("csrrs x0, 0x305, $0" :: "r"(bits) :: "volatile"),
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
+
+/// Clears the CSR
+#[cfg_attr(not(target_arch = "riscv"), allow(unused_variables))]
+#[inline]
+unsafe fn clear(bits: usize) {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => asm!("csrrc x0, 0x305, $0" :: "r"(bits) :: "volatile"),
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
+
+macro_rules! set_csr {
+    ($set_field:ident, $e:expr) => {
+        #[inline]
+        pub unsafe fn $set_field() {
+            set($e);
+        }
+    }
+}
+
+macro_rules! clear_csr {
+    ($clear_field:ident, $e:expr) => {
+        #[inline]
+        pub unsafe fn $clear_field() {
+            clear($e);
+        }
+    }
+}
+
+macro_rules! set_clear_csr {
+    ($set_field:ident, $clear_field:ident, $e:expr) => {
+        set_csr!($set_field, $e);
+        clear_csr!($clear_field, $e);
+    }
+}
+
+/// User Interrupt Enable
+set_clear_csr!(set_uie, clear_uie, 1 << 0);
+/// Supervisor Interrupt Enable
+set_clear_csr!(set_sie, clear_sie, 1 << 1);
+/// Machine Interrupt Enable
+set_clear_csr!(set_mie, clear_mie, 1 << 3);
+/// User Previous Interrupt Enable
+set_csr!(set_upie, 1 << 4);
+/// Supervisor Previous Interrupt Enable
+set_csr!(set_spie, 1 << 5);
+/// Machine Previous Interrupt Enable
+set_csr!(set_mpie, 1 << 7);
+/// Supervisor Previous Privilege Mode
+#[inline]
+pub unsafe fn set_spp(spp: SPP) {
+    set((spp as usize) << 8);
+}
+/// Machine Previous Privilege Mode
+#[inline]
+pub unsafe fn set_mpp(mpp: MPP) {
+    set((mpp as usize) << 11);
+}
diff --git a/src/register/mtvec.rs b/src/register/mtvec.rs
new file mode 100644
index 0000000..393e0f7
--- /dev/null
+++ b/src/register/mtvec.rs
@@ -0,0 +1,65 @@
+//! mtvec register
+
+/// mtvec register
+#[derive(Clone, Copy, Debug)]
+pub struct Mtvec {
+    bits: usize,
+}
+
+/// Trap mode
+pub enum TrapMode {
+    Direct = 0,
+    Vectored = 1,
+}
+
+impl Mtvec {
+    /// Returns the contents of the register as raw bits
+    pub fn bits(&self) -> usize {
+        self.bits
+    }
+
+    /// Returns the trap-vector base-address
+    pub fn address(&self) -> usize {
+        self.bits - (self.bits & 0b11)
+    }
+
+    /// Returns the trap-vector mode
+    pub fn trap_mode(&self) -> TrapMode {
+        let mode = self.bits & 0b11;
+        match mode {
+            0 => TrapMode::Direct,
+            1 => TrapMode::Vectored,
+            _ => unimplemented!()
+        }
+    }
+}
+
+/// Reads the CSR
+#[inline]
+pub fn read() -> Mtvec {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => {
+            let r: usize;
+            unsafe {
+                asm!("csrrs $0, 0x305, x0" : "=r"(r) ::: "volatile");
+            }
+            Mtvec { bits: r }
+        }
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
+
+/// Writes the CSR
+#[cfg_attr(not(target_arch = "riscv"), allow(unused_variables))]
+#[inline]
+pub unsafe fn write(addr: usize, mode: TrapMode) {
+    let bits = addr + mode as usize;
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => asm!("csrrw x0, 0x305, $0" :: "r"(bits) :: "volatile"),
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}
diff --git a/src/register/mvendorid.rs b/src/register/mvendorid.rs
new file mode 100644
index 0000000..9c56735
--- /dev/null
+++ b/src/register/mvendorid.rs
@@ -0,0 +1,42 @@
+//! mvendorid register
+
+/// mvendorid register
+#[derive(Clone, Copy, Debug)]
+pub struct Mvendorid {
+    bits: usize,
+}
+
+impl Mvendorid {
+    /// Returns the contents of the register as raw bits
+    pub fn bits(&self) -> usize {
+        self.bits
+    }
+
+    /// Returns the JEDEC manufacturer ID
+    pub fn jedec_manufacturer(&self) -> usize {
+        self.bits >> 7
+    }
+}
+
+/// Reads the CSR
+#[inline]
+pub fn read() -> Option<Mvendorid> {
+    match () {
+        #[cfg(target_arch = "riscv")]
+        () => {
+            let r: usize;
+            unsafe {
+                asm!("csrrs $0, 0xF11, x0" : "=r"(r) ::: "volatile");
+            }
+            // When mvendorid is hardwired to zero it means that the mvendorid
+            // csr isn't implemented.
+            if r == 0 {
+                None
+            } else {
+                Some(Mvendorid { bits: r })
+            }
+        }
+        #[cfg(not(target_arch = "riscv"))]
+        () => unimplemented!(),
+    }
+}