boot/stm32: autodetect thumbv6, remove cargo feature.

embassy-boot/stm32/Cargo.toml

@@ -27,7 +27,6 @@ defmt = [
     "embassy-stm32/defmt",
 ]
 debug = ["defmt-rtt"]
-thumbv6 = []
 
 [profile.dev]
 debug = 2

embassy-boot/stm32/build.rs

@@ -24,4 +24,9 @@ fn main() {
     if env::var("CARGO_FEATURE_DEFMT").is_ok() {
         println!("cargo:rustc-link-arg-bins=-Tdefmt.x");
     }
+
+    let target = env::var("TARGET").unwrap();
+    if target.starts_with("thumbv6m-") {
+        println!("cargo:rustc-cfg=armv6m");
+    }
 }

embassy-boot/stm32/src/lib.rs

@@ -76,7 +76,7 @@ impl<const PAGE_SIZE: usize> BootLoader<PAGE_SIZE> {
         trace!("Loading app at 0x{:x}", start);
         #[allow(unused_mut)]
         let mut p = cortex_m::Peripherals::steal();
-        #[cfg(not(feature = "thumbv6"))]
+        #[cfg(not(armv6m))]
         p.SCB.invalidate_icache();
         p.SCB.vtor.write(start as u32);