rp/multicore: enable fpu on second core only if building for -eabihf …

…targets.

embassy-rp/build.rs

@@ -1,7 +1,8 @@
 use std::env;
+use std::ffi::OsStr;
 use std::fs::File;
 use std::io::Write;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 fn main() {
     if env::var("CARGO_FEATURE_RP2040").is_ok() {
@@ -16,4 +17,23 @@ fn main() {
         println!("cargo:rerun-if-changed=build.rs");
         println!("cargo:rerun-if-changed=link-rp.x.in");
     }
+
+    // code below taken from https://github.com/rust-embedded/cortex-m/blob/master/cortex-m-rt/build.rs
+
+    let mut target = env::var("TARGET").unwrap();
+
+    // When using a custom target JSON, `$TARGET` contains the path to that JSON file. By
+    // convention, these files are named after the actual target triple, eg.
+    // `thumbv7m-customos-elf.json`, so we extract the file stem here to allow custom target specs.
+    let path = Path::new(&target);
+    if path.extension() == Some(OsStr::new("json")) {
+        target = path
+            .file_stem()
+            .map_or(target.clone(), |stem| stem.to_str().unwrap().to_string());
+    }
+
+    println!("cargo::rustc-check-cfg=cfg(has_fpu)");
+    if target.ends_with("-eabihf") {
+        println!("cargo:rustc-cfg=has_fpu");
+    }
 }

embassy-rp/src/multicore.rs

@@ -170,7 +170,7 @@ where
         };
 
         // Enable FPU
-        #[cfg(feature = "_rp235x")]
+        #[cfg(all(feature = "_rp235x", has_fpu))]
         unsafe {
             let p = cortex_m::Peripherals::steal();
             p.SCB.cpacr.modify(|cpacr| cpacr | (3 << 20) | (3 << 22));