Make rtc optional

This relies on an external dependecy.
Better make it optional to be able to reduce reliance
on external dependencies.

Author: Sh3Rm4n

CHANGELOG.md

@@ -18,6 +18,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Support cortex-m-rt `v0.7.0` but still allow `v0.6.13` ([#283])
 
+### Breaking Changes
+
+- Make `rtc` an optional feature. Without that feature `rtcc` as a dependency is
+  not needed. ([#283])
+
 ## [v0.8.0] - 2021-08-16
 
 ### Added

Cargo.toml

@@ -42,7 +42,7 @@ embedded-hal = { version = "0.2.5", features = ["unproven"] }
 embedded-time = "0.12.0"
 nb = "1.0.0"
 paste = "1.0.5"
-rtcc = "0.2.1"
+rtcc = { version = "0.2.1", optional = true }
 stm32f3 = { version = "0.13.2", default-features = false }
 bxcan = { version = ">=0.4, <0.6", optional = true }
 stm32-usbd = { version = "0.6.0", optional = true }
@@ -73,6 +73,7 @@ ld = []
 rt = ["stm32f3/rt"]
 can = ["bxcan"]
 usb = ["stm32-usbd"]
+rtc = ["rtcc"]
 
 svd-f301 = ["stm32f3/stm32f301"]
 svd-f302 = ["stm32f3/stm32f302"]

src/lib.rs

@@ -82,6 +82,10 @@
 
  Enable USB peripherals on supported targets via the [`stm32-usbd`](https://crates.io/crates/sttm32-usbd) crate.
 
+ ### `rtc`
+
+ Enables RTC support, build upon [`rtcc`](https://crates.io/crates/rtcc) crate.
+
  ### `enumset`
 
  Enable functions, which leverage [`enumset`](https://crates.io/crates/enumset).
@@ -180,6 +184,8 @@ pub mod interrupts;
 pub mod prelude;
 pub mod pwm;
 pub mod rcc;
+#[cfg(feature = "rtc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rtc")))]
 pub mod rtc;
 pub mod serial;
 pub mod spi;