Mark pipe descriptor register memory as volatile.

Most of the values in the descriptor memory can be modified by the
hardware, so we need to tell Rust that.

Also, refactor the common register setup code into `register.rs`.

1 files changed, 1 insertions, 0 deletions

diff --git a/Cargo.toml b/Cargo.toml
index 8d37175..869801c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,6 +16,7 @@ starb = "~0.3"
 log = "~0.4"
 embedded-hal = "~0.2"
 atsamd-hal = "~0.7"
+vcell = "~0.1"
 
 [dev-dependencies.atsamd-hal]
 version = "~0.7"