CSR miselect/mireg: Supervisor indirect register select/alias (#18)

Implement external interrupt CSRs miselect/mireg:

- miselect: Machine indirect register select
- mireg: Machine indirect register alias

These CSRs are specified in the RISC-V Advanced Interrupt Architecture
(AIA) (https://github.com/riscv/riscv-aia/releases).

src/register/mireg.rs

@@ -0,0 +1,161 @@
+//! mireg register
+//!
+//! The `mireg` CSR is defined in "The RISC-V Advanced Interrupt
+//! Architecture" Version 1.0-RC2
+//!
+//! Advanced Interrupt Architecture control is specified using an
+//! indirect register file. In order to access to the register file,
+//! software must:
+//!
+//! (1) Write to the `miselect` CSR with the index of the register to
+//!     access
+//! (2) Access the `mireg` CSR, which now contains the register to
+//!     access
+//!
+//! The functions implemented in this module all write to the `miselect`
+//! CSR to select the indirect register, then perform the read, write,
+//! or modify operation requested on the `mireg` CSR.
+
+use crate::register::miselect;
+use bit_field::BitField;
+
+/// External interrupt delivery enable register
+#[derive(Clone, Copy, Debug)]
+pub struct Eidelivery {
+    bits: usize,
+}
+
+impl Eidelivery {
+    /// Returns the contents of the register as raw bits
+    #[inline]
+    pub fn bits(&self) -> usize {
+        self.bits
+    }
+
+    /// Interrupt delivery is enabled
+    #[inline]
+    pub fn enabled(&self) -> bool {
+        self.bits.get_bit(0)
+    }
+
+    /// Interrupt delivery from a PLIC or APLIC is enabled
+    #[inline]
+    pub fn plic_enabled(&self) -> bool {
+        self.bits.get_bit(30)
+    }
+}
+
+/// Read the supervisor external interrupt delivery enable register
+pub fn read_eidelivery() -> Eidelivery {
+    miselect::write(miselect::Register::Eidelivery);
+    Eidelivery {
+        bits: unsafe { _read() },
+    }
+}
+
+/// Write the supervisor external interrupt delivery enable register
+pub fn write_eidelivery(value: usize) {
+    miselect::write(miselect::Register::Eidelivery);
+    unsafe {
+        _write(value);
+    }
+}
+
+/// Read the supervisor external interrupt threshold register
+pub fn read_eithreshold() -> usize {
+    miselect::write(miselect::Register::Eithreshold);
+    unsafe { _read() }
+}
+
+/// Write the supervisor external interrupt threshold register
+pub fn write_eithreshold(value: usize) {
+    miselect::write(miselect::Register::Eithreshold);
+    unsafe {
+        _write(value);
+    }
+}
+
+/// Determine the register offset and bit position for the external
+/// interrupt pending and external interrupt enabled registers
+#[cfg(riscv32)]
+fn int_register_bit(interrupt: usize) -> (usize, usize) {
+    // On 32-bit RISC-V:
+    // - Each register is 32 bits wide
+    // - Even and odd registers both exist
+    let register = interrupt / 32;
+    let bit = interrupt % 32;
+    (register, bit)
+}
+
+/// Determine the register offset and bit position for the external
+/// interrupt pending and external interrupt enabled registers
+#[cfg(not(riscv32))]
+fn int_register_bit(interrupt: usize) -> (usize, usize) {
+    // On 64-bit RISC-V:
+    // - Each register is 64 bits wide
+    // - Only the even-numbered registers exist
+    let register = (interrupt / 64) * 2;
+    let bit = interrupt % 64;
+    (register, bit)
+}
+
+/// Read the supervisor external interrupt pending bit for the given
+/// external interrupt
+pub fn read_eip(interrupt: usize) -> bool {
+    let (register, bit) = int_register_bit(interrupt);
+    miselect::write_usize(miselect::Register::Eip0 as usize + register);
+    (unsafe { _read() } >> bit) & 1 == 1
+}
+
+/// Set the supervisor external interrupt pending bit for the given
+/// external interrupt
+pub fn set_eip(interrupt: usize) {
+    let (register, bit) = int_register_bit(interrupt);
+    miselect::write_usize(miselect::Register::Eip0 as usize + register);
+    unsafe {
+        _set(1 << bit);
+    }
+}
+
+/// Clear the supervisor external interrupt pending bit for the given
+/// external interrupt
+pub fn clear_eip(interrupt: usize) {
+    let (register, bit) = int_register_bit(interrupt);
+    miselect::write_usize(miselect::Register::Eip0 as usize + register);
+    unsafe {
+        _clear(1 << bit);
+    }
+}
+
+/// Read the supervisor external interrupt enable bit for the given
+/// external interrupt
+pub fn read_eie(interrupt: usize) -> bool {
+    let (register, bit) = int_register_bit(interrupt);
+    miselect::write_usize(miselect::Register::Eie0 as usize + register);
+    (unsafe { _read() } >> bit) & 1 == 1
+}
+
+/// Set the supervisor external interrupt enable bit for the given
+/// external interrupt
+pub fn set_eie(interrupt: usize) {
+    let (register, bit) = int_register_bit(interrupt);
+    miselect::write_usize(miselect::Register::Eie0 as usize + register);
+    unsafe {
+        _set(1 << bit);
+    }
+}
+
+/// Clear the supervisor external interrupt enable bit for the given
+/// external interrupt
+pub fn clear_eie(interrupt: usize) {
+    let (register, bit) = int_register_bit(interrupt);
+    miselect::write_usize(miselect::Register::Eie0 as usize + register);
+    unsafe {
+        _clear(1 << bit);
+    }
+}
+
+read_csr!(0x351);
+write_csr!(0x351);
+set!(0x351);
+clear!(0x351);

src/register/miselect.rs

@@ -0,0 +1,156 @@
+//! miselect register
+//!
+//! The `miselect` CSR is defined in "The RISC-V Advanced Interrupt
+//! Architecture" Version 1.0-RC2
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub enum Register {
+    Eidelivery = 0x70,
+    Eithreshold = 0x72,
+    Eip0 = 0x80,
+    Eip1 = 0x81,
+    Eip2 = 0x82,
+    Eip3 = 0x83,
+    Eip4 = 0x84,
+    Eip5 = 0x85,
+    Eip6 = 0x86,
+    Eip7 = 0x87,
+    Eip8 = 0x88,
+    Eip9 = 0x89,
+    Eip10 = 0x8a,
+    Eip11 = 0x8b,
+    Eip12 = 0x8c,
+    Eip13 = 0x8d,
+    Eip14 = 0x8e,
+    Eip15 = 0x8f,
+    Eip16 = 0x90,
+    Eip17 = 0x91,
+    Eip18 = 0x92,
+    Eip19 = 0x93,
+    Eip20 = 0x94,
+    Eip21 = 0x95,
+    Eip22 = 0x96,
+    Eip23 = 0x97,
+    Eip24 = 0x98,
+    Eip25 = 0x99,
+    Eip26 = 0x9a,
+    Eip27 = 0x9b,
+    Eip28 = 0x9c,
+    Eip29 = 0x9d,
+    Eip30 = 0x9e,
+    Eip31 = 0x9f,
+    Eip32 = 0xa0,
+    Eip33 = 0xa1,
+    Eip34 = 0xa2,
+    Eip35 = 0xa3,
+    Eip36 = 0xa4,
+    Eip37 = 0xa5,
+    Eip38 = 0xa6,
+    Eip39 = 0xa7,
+    Eip40 = 0xa8,
+    Eip41 = 0xa9,
+    Eip42 = 0xaa,
+    Eip43 = 0xab,
+    Eip44 = 0xac,
+    Eip45 = 0xad,
+    Eip46 = 0xae,
+    Eip47 = 0xaf,
+    Eip48 = 0xb0,
+    Eip49 = 0xb1,
+    Eip50 = 0xb2,
+    Eip51 = 0xb3,
+    Eip52 = 0xb4,
+    Eip53 = 0xb5,
+    Eip54 = 0xb6,
+    Eip55 = 0xb7,
+    Eip56 = 0xb8,
+    Eip57 = 0xb9,
+    Eip58 = 0xba,
+    Eip59 = 0xbb,
+    Eip60 = 0xbc,
+    Eip61 = 0xbd,
+    Eip62 = 0xbe,
+    Eip63 = 0xbf,
+    Eie0 = 0xc0,
+    Eie1 = 0xc1,
+    Eie2 = 0xc2,
+    Eie3 = 0xc3,
+    Eie4 = 0xc4,
+    Eie5 = 0xc5,
+    Eie6 = 0xc6,
+    Eie7 = 0xc7,
+    Eie8 = 0xc8,
+    Eie9 = 0xc9,
+    Eie10 = 0xca,
+    Eie11 = 0xcb,
+    Eie12 = 0xcc,
+    Eie13 = 0xcd,
+    Eie14 = 0xce,
+    Eie15 = 0xcf,
+    Eie16 = 0xd0,
+    Eie17 = 0xd1,
+    Eie18 = 0xd2,
+    Eie19 = 0xd3,
+    Eie20 = 0xd4,
+    Eie21 = 0xd5,
+    Eie22 = 0xd6,
+    Eie23 = 0xd7,
+    Eie24 = 0xd8,
+    Eie25 = 0xd9,
+    Eie26 = 0xda,
+    Eie27 = 0xdb,
+    Eie28 = 0xdc,
+    Eie29 = 0xdd,
+    Eie30 = 0xde,
+    Eie31 = 0xdf,
+    Eie32 = 0xe0,
+    Eie33 = 0xe1,
+    Eie34 = 0xe2,
+    Eie35 = 0xe3,
+    Eie36 = 0xe4,
+    Eie37 = 0xe5,
+    Eie38 = 0xe6,
+    Eie39 = 0xe7,
+    Eie40 = 0xe8,
+    Eie41 = 0xe9,
+    Eie42 = 0xea,
+    Eie43 = 0xeb,
+    Eie44 = 0xec,
+    Eie45 = 0xed,
+    Eie46 = 0xee,
+    Eie47 = 0xef,
+    Eie48 = 0xf0,
+    Eie49 = 0xf1,
+    Eie50 = 0xf2,
+    Eie51 = 0xf3,
+    Eie52 = 0xf4,
+    Eie53 = 0xf5,
+    Eie54 = 0xf6,
+    Eie55 = 0xf7,
+    Eie56 = 0xf8,
+    Eie57 = 0xf9,
+    Eie58 = 0xfa,
+    Eie59 = 0xfb,
+    Eie60 = 0xfc,
+    Eie61 = 0xfd,
+    Eie62 = 0xfe,
+    Eie63 = 0xff,
+}
+
+#[inline]
+pub fn write(register: Register) {
+    unsafe { _write(register as usize) };
+}
+
+#[inline]
+pub fn write_usize(register: usize) {
+    unsafe { _write(register) };
+}
+
+#[inline]
+pub fn read() -> usize {
+    unsafe { _read() }
+}
+
+read_csr!(0x350);
+write_csr!(0x350);

src/register/mod.rs

@@ -89,6 +89,8 @@ pub mod mscratch;
 pub mod mtval;
 
 // Machine-Level Interrupts
+pub mod mireg;
+pub mod miselect;
 pub mod mtopei;
 
 // Machine Configuration