Add optional DCD section in linker script

Users can define their device configuration data (DCD), and place the
data in the .dcd section. If the .dcd section has content, the entry in
the IVT points at the user's DCD. This plays well with imxrt-dcd.

2 files changed, 20 insertions, 0 deletions

diff --git a/board/Cargo.toml b/board/Cargo.toml
index 21defd4..9072274 100644
--- a/board/Cargo.toml
+++ b/board/Cargo.toml
@@ -45,3 +45,8 @@ imxrt1170evk-cm7 = [
     "dep:rtt-target",
     "dep:panic-rtt-target",
 ]
+
+# Dummy boards for testing DCD linking.
+# Don't try running these on hardware; they might not work.
+__dcd = ["teensy4"]
+__dcd_missize = ["teensy4"]
diff --git a/board/src/teensy4.rs b/board/src/teensy4.rs
index 28587cd..2aaee82 100644
--- a/board/src/teensy4.rs
+++ b/board/src/teensy4.rs
@@ -35,3 +35,18 @@ pub fn prepare(timer_delay_microseconds: u32) -> Option<crate::Resources> {
         pit,
     })
 }
+
+/// Dummy DCD section containing a single NOP command (for testing linker scripts).
+#[cfg(feature = "__dcd")]
+#[link_section = ".dcd"]
+#[no_mangle]
+#[used]
+pub static DEVICE_CONFIGURATION_DATA: [u8; 8] = [0xD2, 0x00, 0x08, 0x41, 0xC0, 0x00, 0x04, 0x00];
+
+/// Ditto but incorrect size (not a multiple of 4 bytes). The linker script should catch this error
+/// and fail the build.
+#[cfg(feature = "__dcd_missize")]
+#[link_section = ".dcd"]
+#[no_mangle]
+#[used]
+pub static DEVICE_CONFIGURATION_DATA: [u8; 7] = [0xD2, 0x00, 0x08, 0x41, 0xC0, 0x00, 0x04];