revise utralib to use features to select the SVD file

utralib/Cargo.toml

@@ -7,11 +7,6 @@ license = "MIT OR Apache-2.0"
 repository = "https://github.com/betrusted-io/xous-core/"
 homepage = "https://betrusted.io/xous-book/"
 
-[features]
-std = []
-
-default_features = ["std"]
-
 # Dependency versions enforced by Cargo.lock.
 [dependencies]
 
@@ -19,4 +14,21 @@ default_features = ["std"]
 svd2utra = "0.1.0"
 
 # UTRA pre-generated version tracker
-# 0.1.0 - betrusted-soc v0.9.9-7-gc809403 without performance profiling
+[features]
+std = []
+
+# This specifies the SVD rev for platform targets
+# Precursor is an FPGA, so the actual hardware register spec can change over time,
+# hence the gitrev is specified as part of the precursor feature spec. We specify
+# every gitrev that we may need to refer back to, so that we're not trying to
+# map utralib version numbers to precursor soc revs -- by having the gitrev exposed,
+# we can directly look up what generated the SVD file we're using without having
+# to go through some manually maintained lookup table of version # to gitrev.
+#
+# SoCs in custom silicon would typically not need the gitrev, since their
+# hardware is immutable.
+precursor-c809403 = []
+precursor-c809403-perflib = []
+
+# Specify a Precusor default so that we can pass packaging CI tests.
+default_features = ["std", "precursor-c809403"]

utralib/build.rs

@@ -1,9 +1,8 @@
-use std::env;
-
 fn main() {
-    let svd_filename = env::var("XOUS_SVD_FILE")
-        .expect("Set the environment variable `XOUS_SVD_FILE` to point to an SVD file");
-    println!("cargo:rerun-if-env-changed=XOUS_SVD_FILE");
+    #[cfg(feature="precursor-c809403")]
+    let svd_filename = "precursor/soc-c809403.svd";
+    #[cfg(feature="precursor-c809403-perflib")]
+    let svd_filename = "precursor/soc-perf-c809403.svd";
 
     let svd_file_path = std::path::Path::new(&svd_filename);
     println!("cargo:rerun-if-changed={}", svd_file_path.canonicalize().unwrap().display());