bsp(atsame54_xpro): Add defmt feature

Author: ianrrees

boards/atsame54_xpro/.cargo/config.toml

@@ -5,10 +5,14 @@ runner = 'arm-none-eabi-gdb'
 [build]
 target = "thumbv7em-none-eabihf"
 rustflags = [
-
    # This is needed if your flash or ram addresses are not aligned to 0x10000 in memory.x
    # See https://github.com/rust-embedded/cortex-m-quickstart/pull/95
    "-C", "link-arg=--nmagic",
 
+   # To use defmt, the linker needs to be provided with this argument.  The BSP
+   # uses build.rs to supply it conditionally, uncomment this line to use it
+   # unconditionally.
+   # "-C", "link-arg=-Tdefmt.x",
+
    "-C", "link-arg=-Tlink.x",
 ]

boards/atsame54_xpro/Cargo.toml

@@ -38,6 +38,8 @@ rtt-target = {version = "0.3", features = ["cortex-m"]}
 
 [features]
 default = ["rt", "atsamd-hal/same54p"]
+# Use DEFMT_LOG environment variable to set logging level, defaults to `error`
+defmt = ["atsamd-hal/defmt"]
 dma = ["atsamd-hal/dma"]
 max-channels = ["dma", "atsamd-hal/max-channels"]
 # Enable async support from atsamd-hal

boards/atsame54_xpro/build.rs

@@ -12,5 +12,8 @@ fn main() {
         println!("cargo:rustc-link-search={}", out.display());
         println!("cargo:rerun-if-changed=memory.x");
     }
+    if env::var_os("CARGO_FEATURE_DEFMT").is_some() {
+        println!("cargo:rustc-link-arg=-Tdefmt.x");
+    }
     println!("cargo:rerun-if-changed=build.rs");
 }