Stop autogenerating config.rs file

Cargo.toml

@@ -28,4 +28,5 @@ default = ["avr-std-stub"]
 
 [dependencies]
 avr-std-stub = { version = "1.0", optional = true }
+const_env--value = "0.1"
 target-cpu-macro = "0.1"

core_generator/src/main.rs

@@ -46,7 +46,6 @@ fn main() {
     };
     let current_mcu_name = current_mcu.device.name.clone();
 
-    generate_config_module().unwrap();
     generate_cores(&[current_mcu]).unwrap();
 
     println!("cargo:rustc-cfg=avr_mcu_{}", normalize_device_name(&current_mcu_name));
@@ -59,23 +58,6 @@ fn generate_cores(mcus: &[Mcu]) -> Result<(), io::Error> {
     generate_cores_mod_rs(mcus)
 }
 
-fn generate_config_module() -> Result<(), io::Error> {
-    let path = base_output_path().join("config.rs");
-    let mut f = File::create(&path)?;
-
-    let clock: u64 = if cfg!(arch = "avr") {
-        env::var("AVR_CPU_FREQUENCY_HZ")
-            .expect("Please set the '$AVR_CPU_FREQUENCY_HZ' environment variable")
-            .parse()
-            .expect("The $AVR_CPU_FREQUENCY_HZ environment variable is not an integer")
-    } else {
-        DEFAULT_FREQUENCY_HZ_FOR_NON_AVR_DOCS
-    };
-    writeln!(f, "/// The clock frequency of device being targeted in Hertz.")?;
-    writeln!(f, "pub const CPU_FREQUENCY_HZ: u32 = {};", clock)?;
-    Ok(())
-}
-
 fn generate_core_module(mcu: &Mcu) -> Result<(), io::Error> {
     let path = cores_path().join(format!("{}.rs", core_module_name(mcu)));
     let mut file = File::create(&path)?;

src/config.rs

@@ -1,2 +1,13 @@
+#[cfg(target_arch = "avr")] use const_env::value_from_env;
+
 /// The clock frequency of device being targeted in Hertz.
-pub const CPU_FREQUENCY_HZ: u32 = 16000000;
+#[cfg(target_arch = "avr")]
+pub const CPU_FREQUENCY_HZ: u32 = value_from_env!("AVR_CPU_FREQUENCY_HZ": u32);
+
+/// The clock frequency of device being targeted in Hertz.
+///
+/// This value is arbitrarily set to 16MHz as this crate is currently being targeted for a non-AVR
+/// device.
+#[cfg(not(target_arch = "avr"))]
+pub const CPU_FREQUENCY_HZ: u32 = 16_000_000; // Choose a nice default when not targeting AVR.
+

src/lib.rs

@@ -11,6 +11,8 @@
 
 #[cfg(feature = "avr-std-stub")] extern crate avr_std_stub;
 
+extern crate const_env__value as const_env;
+
 pub use self::register::{Register, RegisterBits, RegisterValue};
 pub use self::pin::{DataDirection, Pin};