RISC-V: Make atomic emulation opt-in

CHANGELOG.md

@@ -13,6 +13,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- C2, C3: atomic emulation trap is now opt-in and `esp-hal` now uses `portable-atomic` by default (#904)
+
 ### Fixed
 
 - ESP32-C2/C3 examples: fix build error (#899)

esp-hal-common/Cargo.toml

@@ -33,6 +33,10 @@ strum                = { version = "0.25.0", default-features = false, features
 void                 = { version = "1.0.2", default-features = false }
 usb-device           = { version = "0.2.9", optional = true }
 
+# atomic polyfill options
+portable-atomic              = { version = "1.5.1", default-features = false, optional = true }
+riscv-atomic-emulation-trap  = { version = "0.4.1", optional = true }
+
 # async
 embedded-hal-async = { version = "=1.0.0-rc.1", optional = true }
 embedded-io-async  = { version = "0.6.0", optional = true }
@@ -43,7 +47,6 @@ embassy-time       = { version = "0.1.5", optional = true, features = ["nightly"
 
 # RISC-V
 esp-riscv-rt                = { version = "0.5.0", optional = true, path = "../esp-riscv-rt" }
-riscv-atomic-emulation-trap = { version = "0.4.1", optional = true }
 
 # Xtensa
 xtensa-lx    = { version = "0.8.0",  optional = true }
@@ -125,9 +128,13 @@ embassy-time-systick = []
 embassy-time-timg0   = []
 
 # Architecture-specific features (intended for internal use)
-riscv  = ["critical-section/restore-state-u8", "esp-riscv-rt", "esp-riscv-rt/zero-bss", "riscv-atomic-emulation-trap"]
+riscv  = ["critical-section/restore-state-u8", "esp-riscv-rt", "esp-riscv-rt/zero-bss"]
 xtensa = ["critical-section/restore-state-u32"]
 
+portable-atomic = ["dep:portable-atomic"]
+riscv-atomic-emulation = ["dep:riscv-atomic-emulation-trap", "atomic-emulation"]
+atomic-emulation = []
+
 # Initialize / clear data sections and RTC memory
 rv-init-data     = ["esp-riscv-rt/init-data", "esp-riscv-rt/init-rw-text"]
 rv-zero-rtc-bss  = ["esp-riscv-rt/zero-rtc-fast-bss"]

esp-hal-common/build.rs

@@ -136,6 +136,28 @@ fn main() -> Result<(), Box<dyn Error>> {
         unreachable!() // We've confirmed exactly one known device was selected
     };
 
+    // The C6 has an "atomic" peripheral but it's an exception, not the rule
+    // For S2, we just keep lying for now. The target has emulation support
+    // force-enabled.
+    let has_native_atomic_support = matches!(
+        device_name,
+        "esp32" | "esp32s2" | "esp32s3" | "esp32c6" | "esp32h2"
+    );
+
+    let atomic_emulation_enabled = cfg!(feature = "atomic-emulation");
+    let portable_atomic_enabled = cfg!(feature = "portable-atomic");
+
+    if atomic_emulation_enabled && portable_atomic_enabled {
+        panic!("The `atomic-emulation` and `portable-atomic` features cannot be used together");
+    }
+
+    if has_native_atomic_support {
+        if atomic_emulation_enabled {
+            println!("cargo:warning={} has native atomic instructions, the `atomic-emulation` feature is not needed", device_name);
+        }
+        println!("cargo:rustc-cfg=has_native_atomic_support");
+    }
+
     // Load the configuration file for the configured device:
     let chip_toml_path = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
         .join("devices")

esp-hal-common/src/embassy/executor/xtensa/interrupt.rs

@@ -1,14 +1,14 @@
 //! Multicore-aware interrupt-mode executor.
-use core::{
-    cell::UnsafeCell,
-    marker::PhantomData,
-    mem::MaybeUninit,
-    sync::atomic::{AtomicUsize, Ordering},
-};
+use core::{cell::UnsafeCell, marker::PhantomData, mem::MaybeUninit};
 
 use embassy_executor::{raw, SendSpawner};
 
-use crate::{get_core, interrupt, peripherals, peripherals::SYSTEM};
+use crate::{
+    atomic::{AtomicUsize, Ordering},
+    get_core,
+    interrupt,
+    peripherals::{self, SYSTEM},
+};
 
 static FROM_CPU_IRQ_USED: AtomicUsize = AtomicUsize::new(0);
 

esp-hal-common/src/embassy/executor/xtensa/thread.rs

@@ -1,12 +1,13 @@
 //! Multicore-aware thread-mode embassy executor.
-use core::{
-    marker::PhantomData,
-    sync::atomic::{AtomicBool, Ordering},
-};
+use core::marker::PhantomData;
 
 use embassy_executor::{raw, Spawner};
 
-use crate::{get_core, prelude::interrupt};
+use crate::{
+    atomic::{AtomicBool, Ordering},
+    get_core,
+    prelude::interrupt,
+};
 #[cfg(multi_core)]
 use crate::{
     interrupt,

esp-hal-common/src/interrupt/riscv.rs

@@ -474,74 +474,77 @@ unsafe fn handle_exception(pc: usize, trap_frame: *mut TrapFrame) {
         return;
     }
 
-    let mut frame = [
-        0,
-        (*trap_frame).ra,
-        (*trap_frame).sp,
-        (*trap_frame).gp,
-        (*trap_frame).tp,
-        (*trap_frame).t0,
-        (*trap_frame).t1,
-        (*trap_frame).t2,
-        (*trap_frame).s0,
-        (*trap_frame).s1,
-        (*trap_frame).a0,
-        (*trap_frame).a1,
-        (*trap_frame).a2,
-        (*trap_frame).a3,
-        (*trap_frame).a4,
-        (*trap_frame).a5,
-        (*trap_frame).a6,
-        (*trap_frame).a7,
-        (*trap_frame).s2,
-        (*trap_frame).s3,
-        (*trap_frame).s4,
-        (*trap_frame).s5,
-        (*trap_frame).s6,
-        (*trap_frame).s7,
-        (*trap_frame).s8,
-        (*trap_frame).s9,
-        (*trap_frame).s10,
-        (*trap_frame).s11,
-        (*trap_frame).t3,
-        (*trap_frame).t4,
-        (*trap_frame).t5,
-        (*trap_frame).t6,
-    ];
-    riscv_atomic_emulation_trap::atomic_emulation((*trap_frame).pc, &mut frame);
-
-    (*trap_frame).ra = frame[1];
-    (*trap_frame).sp = frame[2];
-    (*trap_frame).gp = frame[3];
-    (*trap_frame).tp = frame[4];
-    (*trap_frame).t0 = frame[5];
-    (*trap_frame).t1 = frame[6];
-    (*trap_frame).t2 = frame[7];
-    (*trap_frame).s0 = frame[8];
-    (*trap_frame).s1 = frame[9];
-    (*trap_frame).a0 = frame[10];
-    (*trap_frame).a1 = frame[11];
-    (*trap_frame).a2 = frame[12];
-    (*trap_frame).a3 = frame[13];
-    (*trap_frame).a4 = frame[14];
-    (*trap_frame).a5 = frame[15];
-    (*trap_frame).a6 = frame[16];
-    (*trap_frame).a7 = frame[17];
-    (*trap_frame).s2 = frame[18];
-    (*trap_frame).s3 = frame[19];
-    (*trap_frame).s4 = frame[20];
-    (*trap_frame).s5 = frame[21];
-    (*trap_frame).s6 = frame[22];
-    (*trap_frame).s7 = frame[23];
-    (*trap_frame).s8 = frame[24];
-    (*trap_frame).s9 = frame[25];
-    (*trap_frame).s10 = frame[26];
-    (*trap_frame).s11 = frame[27];
-    (*trap_frame).t3 = frame[28];
-    (*trap_frame).t4 = frame[29];
-    (*trap_frame).t5 = frame[30];
-    (*trap_frame).t6 = frame[31];
-    (*trap_frame).pc = pc + 4;
+    #[cfg(feature = "atomic-emulation")]
+    {
+        let mut frame = [
+            0,
+            (*trap_frame).ra,
+            (*trap_frame).sp,
+            (*trap_frame).gp,
+            (*trap_frame).tp,
+            (*trap_frame).t0,
+            (*trap_frame).t1,
+            (*trap_frame).t2,
+            (*trap_frame).s0,
+            (*trap_frame).s1,
+            (*trap_frame).a0,
+            (*trap_frame).a1,
+            (*trap_frame).a2,
+            (*trap_frame).a3,
+            (*trap_frame).a4,
+            (*trap_frame).a5,
+            (*trap_frame).a6,
+            (*trap_frame).a7,
+            (*trap_frame).s2,
+            (*trap_frame).s3,
+            (*trap_frame).s4,
+            (*trap_frame).s5,
+            (*trap_frame).s6,
+            (*trap_frame).s7,
+            (*trap_frame).s8,
+            (*trap_frame).s9,
+            (*trap_frame).s10,
+            (*trap_frame).s11,
+            (*trap_frame).t3,
+            (*trap_frame).t4,
+            (*trap_frame).t5,
+            (*trap_frame).t6,
+        ];
+        riscv_atomic_emulation_trap::atomic_emulation((*trap_frame).pc, &mut frame);
+
+        (*trap_frame).ra = frame[1];
+        (*trap_frame).sp = frame[2];
+        (*trap_frame).gp = frame[3];
+        (*trap_frame).tp = frame[4];
+        (*trap_frame).t0 = frame[5];
+        (*trap_frame).t1 = frame[6];
+        (*trap_frame).t2 = frame[7];
+        (*trap_frame).s0 = frame[8];
+        (*trap_frame).s1 = frame[9];
+        (*trap_frame).a0 = frame[10];
+        (*trap_frame).a1 = frame[11];
+        (*trap_frame).a2 = frame[12];
+        (*trap_frame).a3 = frame[13];
+        (*trap_frame).a4 = frame[14];
+        (*trap_frame).a5 = frame[15];
+        (*trap_frame).a6 = frame[16];
+        (*trap_frame).a7 = frame[17];
+        (*trap_frame).s2 = frame[18];
+        (*trap_frame).s3 = frame[19];
+        (*trap_frame).s4 = frame[20];
+        (*trap_frame).s5 = frame[21];
+        (*trap_frame).s6 = frame[22];
+        (*trap_frame).s7 = frame[23];
+        (*trap_frame).s8 = frame[24];
+        (*trap_frame).s9 = frame[25];
+        (*trap_frame).s10 = frame[26];
+        (*trap_frame).s11 = frame[27];
+        (*trap_frame).t3 = frame[28];
+        (*trap_frame).t4 = frame[29];
+        (*trap_frame).t5 = frame[30];
+        (*trap_frame).t6 = frame[31];
+        (*trap_frame).pc = pc + 4;
+    }
 }
 
 #[doc(hidden)]

esp-hal-common/src/lib.rs

@@ -161,6 +161,12 @@ pub mod trapframe {
 // be directly exposed.
 mod soc;
 
+#[cfg(any(has_native_atomic_support, feature = "atomic-emulation"))]
+use core::sync::atomic;
+
+#[cfg(feature = "portable-atomic")]
+use portable_atomic as atomic;
+
 #[no_mangle]
 extern "C" fn EspDefaultHandler(_level: u32, _interrupt: peripherals::Interrupt) {
     #[cfg(feature = "log")]
@@ -317,7 +323,7 @@ mod critical_section_impl {
 
     #[cfg(multi_core)]
     mod multicore {
-        use core::sync::atomic::{AtomicUsize, Ordering};
+        use crate::atomic::{AtomicUsize, Ordering};
 
         // We're using a value that we know get_raw_core() will never return. This
         // avoids an unnecessary increment of the core ID.

esp32-hal/Cargo.toml

@@ -47,7 +47,7 @@ lis3dh-async       = "0.8.0"
 sha2               = { version = "0.10.8", default-features = false}
 smart-leds         = "0.3.0"
 ssd1306            = "0.8.4"
-static_cell        = { version = "=1.2.0", features = ["nightly"] }
+static_cell        = { version = "2.0.0", features = ["nightly"] }
 
 [features]
 default            = ["rt", "vectored", "xtal-40mhz"]

esp32c2-hal/.cargo/config.toml

@@ -3,22 +3,6 @@ runner = "espflash flash --monitor"
 rustflags = [
   "-C", "link-arg=-Tlinkall.x",
   "-C", "force-frame-pointers",
-
-  # comment the cfgs below if you do _not_ wish to emulate atomics.
-  # enable the atomic codegen option for RISCV
-  "-C", "target-feature=+a",
-  # tell the core library have atomics even though it's not specified in the target definition
-  "--cfg", "target_has_atomic_load_store",
-  "--cfg", 'target_has_atomic_load_store="8"',
-  "--cfg", 'target_has_atomic_load_store="16"',
-  "--cfg", 'target_has_atomic_load_store="32"',
-  "--cfg", 'target_has_atomic_load_store="ptr"',
-  # enable cas
-  "--cfg", "target_has_atomic",
-  "--cfg", 'target_has_atomic="8"',
-  "--cfg", 'target_has_atomic="16"',
-  "--cfg", 'target_has_atomic="32"',
-  "--cfg", 'target_has_atomic="ptr"',
 ]
 
 [build]

esp32c2-hal/Cargo.toml

@@ -41,7 +41,7 @@ heapless           = "0.7.16"
 lis3dh-async       = "0.8.0"
 sha2               = { version = "0.10.8", default-features = false}
 ssd1306            = "0.8.4"
-static_cell        = { version = "=1.2.0", features = ["nightly"] }
+static_cell        = { version = "2.0.0", features = ["nightly"] }
 hex-literal       = "0.4.1"
 crypto-bigint     = {version = "0.5.3", default-features = false }
 elliptic-curve    = {version = "0.13.6", default-features = false, features = ["sec1"] }
@@ -50,7 +50,7 @@ p256              = {version = "0.13.2", default-features = false, features = ["
 embassy-sync       = "0.3.0"
 
 [features]
-default              = ["rt", "vectored", "xtal-40mhz"]
+default              = ["rt", "vectored", "xtal-40mhz", "portable-atomic"]
 async                = ["esp-hal-common/async"]
 debug                = ["esp-hal-common/debug"]
 defmt                = ["esp-hal-common/defmt", "esp-println/defmt"]
@@ -70,6 +70,9 @@ embassy              = ["esp-hal-common/embassy"]
 embassy-time-systick = ["esp-hal-common/embassy-time-systick", "embassy-time/tick-hz-16_000_000"]
 embassy-time-timg0   = ["esp-hal-common/embassy-time-timg0",   "embassy-time/tick-hz-1_000_000"]
 
+portable-atomic  = ["esp-hal-common/portable-atomic"]
+atomic-emulation = ["esp-hal-common/riscv-atomic-emulation"]
+
 [profile.release]
 debug = true
 

esp32c3-hal/.cargo/config.toml

@@ -3,22 +3,6 @@ runner = "espflash flash --monitor"
 rustflags = [
   "-C", "link-arg=-Tlinkall.x",
   "-C", "force-frame-pointers",
-
-  # comment the cfgs below if you do _not_ wish to emulate atomics.
-  # enable the atomic codegen option for RISCV
-  "-C", "target-feature=+a",
-  # tell the core library have atomics even though it's not specified in the target definition
-  "--cfg", "target_has_atomic_load_store",
-  "--cfg", 'target_has_atomic_load_store="8"',
-  "--cfg", 'target_has_atomic_load_store="16"',
-  "--cfg", 'target_has_atomic_load_store="32"',
-  "--cfg", 'target_has_atomic_load_store="ptr"',
-  # enable cas
-  "--cfg", "target_has_atomic",
-  "--cfg", 'target_has_atomic="8"',
-  "--cfg", 'target_has_atomic="16"',
-  "--cfg", 'target_has_atomic="32"',
-  "--cfg", 'target_has_atomic="ptr"',
 ]
 
 [build]

esp32c3-hal/Cargo.toml

@@ -49,11 +49,11 @@ lis3dh-async       = "0.8.0"
 sha2               = { version = "0.10.8", default-features = false }
 smart-leds         = "0.3.0"
 ssd1306            = "0.8.4"
-static_cell        = { version = "=1.2.0", features = ["nightly"] }
+static_cell        = { version = "2.0.0", features = ["nightly"] }
 embassy-sync       = "0.3.0"
 
 [features]
-default              = ["rt", "vectored", "esp-hal-common/rv-zero-rtc-bss"]
+default              = ["rt", "vectored", "esp-hal-common/rv-zero-rtc-bss", "portable-atomic"]
 async                = ["esp-hal-common/async"]
 debug                = ["esp-hal-common/debug"]
 defmt                = ["esp-hal-common/defmt", "esp-println/defmt"]
@@ -72,6 +72,9 @@ embassy              = ["esp-hal-common/embassy"]
 embassy-time-systick = ["esp-hal-common/embassy-time-systick", "embassy-time/tick-hz-16_000_000"]
 embassy-time-timg0   = ["esp-hal-common/embassy-time-timg0", "embassy-time/tick-hz-1_000_000"]
 
+portable-atomic  = ["esp-hal-common/portable-atomic"]
+atomic-emulation = ["esp-hal-common/riscv-atomic-emulation"]
+
 [profile.release]
 debug = true
 

esp32c6-hal/Cargo.toml

@@ -48,7 +48,7 @@ lis3dh-async       = "0.8.0"
 sha2               = { version = "0.10.8", default-features = false}
 smart-leds         = "0.3.0"
 ssd1306            = "0.8.4"
-static_cell        = { version = "=1.2.0", features = ["nightly"] }
+static_cell        = { version = "2.0.0", features = ["nightly"] }
 hex-literal       = "0.4.1"
 elliptic-curve    = {version = "0.13.6", default-features = false, features = ["sec1"] }
 p192              = {version = "0.13.0", default-features = false, features = ["arithmetic"] }