Provide arch module on RP2040

This improves code portability between rp2040-hal and rp235x-hal

rp2040-hal-examples/src/bin/pio_side_set.rs

@@ -65,6 +65,6 @@ fn main() -> ! {
 
     // PIO runs in background, independently from CPU
     loop {
-        cortex_m::asm::wfi();
+        hal::arch::wfi();
     }
 }

rp2040-hal/src/arch.rs

@@ -0,0 +1,68 @@
+//! Portable in-line assembly
+//!
+//! On the RP235x, this is useful to write code portable between ARM and RISC-V cores.
+//! While there's no such choice on the RP2040, providing the same functions helps writing
+//! code that works on both RP2040 and RP235x.
+
+#[cfg(all(target_arch = "arm", target_os = "none"))]
+mod inner {
+    pub use cortex_m::asm::{delay, dsb, nop, sev, wfe, wfi};
+    pub use cortex_m::interrupt::{disable as interrupt_disable, enable as interrupt_enable};
+
+    /// Are interrupts current enabled?
+    pub fn interrupts_enabled() -> bool {
+        cortex_m::register::primask::read().is_active()
+    }
+
+    /// Run the closure without interrupts
+    ///
+    /// No critical-section token because we haven't blocked the second core
+    pub fn interrupt_free<T, F>(f: F) -> T
+    where
+        F: FnOnce() -> T,
+    {
+        let active = interrupts_enabled();
+        if active {
+            interrupt_disable();
+        }
+        let t = f();
+        if active {
+            unsafe {
+                interrupt_enable();
+            }
+        }
+        t
+    }
+}
+
+#[cfg(not(all(any(target_arch = "arm", target_arch = "riscv32"), target_os = "none")))]
+mod inner {
+    /// Placeholder function to disable interrupts
+    pub fn interrupt_disable() {}
+    /// Placeholder function to enable interrupts
+    pub fn interrupt_enable() {}
+    /// Placeholder function to check if interrupts are enabled
+    pub fn interrupts_enabled() -> bool {
+        false
+    }
+    /// Placeholder function to wait for an event
+    pub fn wfe() {}
+    /// Placeholder function to do nothing
+    pub fn nop() {}
+    /// Placeholder function to emit a data synchronisation barrier
+    pub fn dsb() {}
+    /// Placeholder function to run a closure with interrupts disabled
+    pub fn interrupt_free<T, F>(f: F) -> T
+    where
+        F: FnOnce() -> T,
+    {
+        f()
+    }
+    /// Placeholder function to wait for some clock cycles
+    pub fn delay(_: u32) {}
+    /// Placeholder function to emit an event
+    pub fn sev() {}
+}
+
+pub use inner::*;
+

rp2040-hal/src/lib.rs

@@ -51,6 +51,7 @@ pub use rp2040_pac as pac;
 mod intrinsics;
 
 pub mod adc;
+pub mod arch;
 #[macro_use]
 pub mod async_utils;
 pub(crate) mod atomic_register_access;