Attempt to fix docs.rs build

Cargo.toml

@@ -93,6 +93,10 @@ optional = true
 # warnings.
 no-target-warning = []
 
+# Indicates to the build script that we're building docs, and it can skip
+# whatever might not work or is not necessary.
+docs = []
+
 # Internal implementation detail. Used by HAL code to determine the exact
 # hardware capabilites.
 20 = []
@@ -188,4 +192,4 @@ opt-level = "s"
 
 
 [package.metadata.docs.rs]
-features = ["845"]
+features = ["845", "docs"]

build.rs

@@ -11,6 +11,16 @@ use termion::{color, style};
 fn main() -> Result<(), Error> {
     let target = Target::read();
 
+    // Nothing this build script does after this point is required when
+    // generating documentation.
+    //
+    // In addition, the docs.rs build environment has a read-only file system,
+    // meaning an attempt to run this build script will fail the whole build for
+    // no reason.
+    if cfg!(feature = "docs") {
+        return Ok(());
+    }
+
     copy_openocd_config(target)?;
     copy_memory_config(target)?;