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Merge pull request #246 from rust-embedded/asm
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`riscv`: align assembly functions with `cortex-m`
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@romancardenas
romancardenas authored Dec 17, 2024
2 parents b3a42fd + 2ba1abf commit 60800c1
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1 change: 1 addition & 0 deletions riscv/CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).

### Changed

- Align assembly functions with `cortex-m`
- Use CSR helper macros to define `marchid` register
- Re-use `try_*` functions in `mcountinhibit`
- Use CSR helper macros to define `mcause` register
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142 changes: 69 additions & 73 deletions riscv/src/asm.rs
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Original file line number Diff line number Diff line change
@@ -1,30 +1,24 @@
//! Assembly instructions
macro_rules! instruction {
($(#[$attr:meta])*, unsafe $fnname:ident, $asm:expr) => (
($(#[$attr:meta])*, unsafe $fnname:ident, $asm:expr, $($options:tt)*) => (
$(#[$attr])*
#[inline]
#[inline(always)]
pub unsafe fn $fnname() {
match () {
#[cfg(riscv)]
() => core::arch::asm!($asm),

#[cfg(not(riscv))]
() => unimplemented!(),
}
#[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
core::arch::asm!($asm, $($options)*);
#[cfg(not(any(target_arch = "riscv32", target_arch = "riscv64")))]
unimplemented!();
}
);
($(#[$attr:meta])*, $fnname:ident, $asm:expr) => (
($(#[$attr:meta])*, $fnname:ident, $asm:expr, $($options:tt)*) => (
$(#[$attr])*
#[inline]
#[inline(always)]
pub fn $fnname() {
match () {
#[cfg(riscv)]
() => unsafe { core::arch::asm!($asm) },

#[cfg(not(riscv))]
() => unimplemented!(),
}
#[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
unsafe { core::arch::asm!($asm, $($options)*) };
#[cfg(not(any(target_arch = "riscv32", target_arch = "riscv64")))]
unimplemented!();
}
);
}
Expand All @@ -37,18 +31,35 @@ instruction!(
///
/// This function generates a no-operation; it's useful to prevent delay loops from being
/// optimized away.
, nop, "nop");
, nop, "nop", options(nomem, nostack));

instruction!(
/// `WFI` instruction wrapper
///
/// Provides a hint to the implementation that the current hart can be stalled until an interrupt might need servicing.
/// The WFI instruction is just a hint, and a legal implementation is to implement WFI as a NOP.
, wfi, "wfi", options(nomem, nostack));

instruction!(
/// `EBREAK` instruction wrapper
///
/// Generates a breakpoint exception.
, unsafe ebreak, "ebreak");
, unsafe ebreak, "ebreak", options(nomem, nostack));

instruction!(
/// `WFI` instruction wrapper
/// `ECALL` instruction wrapper
///
/// Provides a hint to the implementation that the current hart can be stalled until an interrupt might need servicing.
/// The WFI instruction is just a hint, and a legal implementation is to implement WFI as a NOP.
, wfi, "wfi");
/// Generates an exception for a service request to the execution environment.
/// When executed in U-mode, S-mode, or M-mode, it generates an environment-call-from-U-mode
/// exception, environment-call-from-S-mode exception, or environment-call-from-M-mode exception,
/// respectively, and performs no other operation.
///
/// # Note
///
/// The ECALL instruction will **NOT** save and restore the stack pointer, as it triggers an exception.
/// The stack pointer must be saved and restored accordingly by the exception handler.
, unsafe ecall, "ecall", options(nomem, nostack));

instruction!(
/// `SFENCE.VMA` instruction wrapper (all address spaces and page table levels)
///
Expand All @@ -57,7 +68,8 @@ instruction!(
/// are ordinarily not ordered with respect to loads and stores in the instruction stream.
/// Executing an `SFENCE.VMA` instruction guarantees that any stores in the instruction stream prior to the
/// `SFENCE.VMA` are ordered before all implicit references subsequent to the `SFENCE.VMA`.
, sfence_vma_all, "sfence.vma");
, sfence_vma_all, "sfence.vma", options(nostack));

instruction!(
/// `FENCE` instruction wrapper
///
Expand All @@ -66,12 +78,12 @@ instruction!(
/// (O), memory reads (R), and memory writes (W) may be ordered with respect to any combination
/// of the same. Informally, no other RISC-V hart or external device can observe any operation in the
/// successor set following a FENCE before any operation in the predecessor set preceding the FENCE.
/// Chapter 17 provides a precise description of the RISC-V memory consistency model.
///
/// The FENCE instruction also orders memory reads and writes made by the hart as observed by
/// memory reads and writes made by an external device. However, FENCE does not order observations
/// of events made by an external device using any other signaling mechanism.
, fence, "fence");
, fence, "fence", options(nostack));

instruction!(
/// `FENCE.I` instruction wrapper
///
Expand All @@ -89,7 +101,7 @@ instruction!(
/// The unused fields in the FENCE.I instruction, imm\[11:0\], rs1, and rd, are reserved for
/// finer-grain fences in future extensions. For forward compatibility, base
/// implementations shall ignore these fields, and standard software shall zero these fields.
, fence_i, "fence.i");
, fence_i, "fence.i", options(nostack));

/// `SFENCE.VMA` instruction wrapper
///
Expand All @@ -98,38 +110,18 @@ instruction!(
/// are ordinarily not ordered with respect to loads and stores in the instruction stream.
/// Executing an `SFENCE.VMA` instruction guarantees that any stores in the instruction stream prior to the
/// `SFENCE.VMA` are ordered before all implicit references subsequent to the `SFENCE.VMA`.
#[inline]
#[allow(unused_variables)]
pub unsafe fn sfence_vma(asid: usize, addr: usize) {
match () {
#[cfg(riscv)]
() => core::arch::asm!("sfence.vma {0}, {1}", in(reg) addr, in(reg) asid),

#[cfg(not(riscv))]
() => unimplemented!(),
}
}

/// `ECALL` instruction wrapper
///
/// Generates an exception for a service request to the execution environment.
/// When executed in U-mode, S-mode, or M-mode, it generates an environment-call-from-U-mode
/// exception, environment-call-from-S-mode exception, or environment-call-from-M-mode exception,
/// respectively, and performs no other operation.
///
/// # Note
///
/// The ECALL instruction will **NOT** save and restore the stack pointer, as it triggers an exception.
/// The stack pointer must be saved and restored accordingly by the exception handler.
#[inline]
pub unsafe fn ecall() {
match () {
#[cfg(riscv)]
() => core::arch::asm!("ecall", options(nostack)),

#[cfg(not(riscv))]
() => unimplemented!(),
}
#[inline(always)]
#[cfg_attr(
not(any(target_arch = "riscv32", target_arch = "riscv64")),
allow(unused_variables)
)]
pub fn sfence_vma(asid: usize, addr: usize) {
#[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
unsafe {
core::arch::asm!("sfence.vma {0}, {1}", in(reg) addr, in(reg) asid, options(nostack));
};
#[cfg(not(any(target_arch = "riscv32", target_arch = "riscv64")))]
unimplemented!();
}

/// Blocks the program for *at least* `cycles` CPU cycles.
Expand All @@ -142,22 +134,26 @@ pub unsafe fn ecall() {
/// timer-less initialization of peripherals if and only if accurate timing is not essential. In
/// any other case please use a more accurate method to produce a delay.
#[inline]
#[allow(unused_variables)]
#[cfg_attr(
not(any(target_arch = "riscv32", target_arch = "riscv64")),
allow(unused_variables)
)]
pub fn delay(cycles: u32) {
match () {
#[cfg(riscv)]
() => unsafe {
#[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
() => {
let real_cyc = 1 + cycles / 2;
core::arch::asm!(
"2:",
"addi {0}, {0}, -1",
"bne {0}, zero, 2b",
inout(reg) real_cyc => _,
options(nomem, nostack),
)
},

#[cfg(not(riscv))]
unsafe {
core::arch::asm!(
"2:",
"addi {0}, {0}, -1",
"bne {0}, zero, 2b",
inout(reg) real_cyc => _,
options(nomem, nostack),
);
}
}
#[cfg(not(any(target_arch = "riscv32", target_arch = "riscv64")))]
() => unimplemented!(),
}
}

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