1 files changed, 52 insertions, 0 deletions
diff --git a/board/src/shared/imxrt11xx.rs b/board/src/shared/imxrt11xx.rs
new file mode 100644
index 0000000..e0d1074
--- /dev/null
+++ b/board/src/shared/imxrt11xx.rs
@@ -0,0 +1,52 @@
+//! Code shared across all i.MX RT 11xx chips.
+
+use crate::ral;
+
+pub(crate) fn prepare_pit(timer_delay_microseconds: u32) -> Option<crate::Pit> {
+    #[cfg(feature = "rtic")]
+    {
+        extern "C" {
+            // Not actually mut in cortex-m. But, no one is reading it...
+            static __INTERRUPTS: [core::cell::UnsafeCell<unsafe extern "C" fn()>; 240];
+            fn PIT();
+        }
+        unsafe {
+            __INTERRUPTS[crate::ral::Interrupt::PIT1 as usize]
+                .get()
+                .write_volatile(PIT);
+        }
+    }
+
+    let ccm = unsafe { ral::ccm::CCM::instance() };
+
+    // Change the bus clock to the 24 MHz XTAL.
+    // Wouldn't recommend doing this in a real system,
+    // since the bus clock is running rather slowly.
+    // But, it's good enough for a demo, and it lets us match
+    // the behaviors of the 10xx examples.
+    //
+    // If we decrease the bus speed too much, we seem to reach a condition
+    // where we can't re-flash the device. Haven't dug too deeply; only
+    // observed that keeping the bus clock faster lets us flash more reliably,
+    // at least with pyOCD.
+    let clock_root_2 = &ccm.CLOCK_ROOT[2];
+    ral::modify_reg!(ral::ccm::clockroot, clock_root_2, CLOCK_ROOT_CONTROL, MUX: 0b001, DIV: 0);
+    while ral::read_reg!(
+        ral::ccm::clockroot,
+        clock_root_2,
+        CLOCK_ROOT_STATUS0,
+        CHANGING == 1
+    ) {}
+
+    // Enable the clock gate to PIT1.
+    ral::write_reg!(ral::ccm, ccm, LPCG61_DIRECT, 1);
+
+    let pit = unsafe { ral::pit::PIT1::instance() };
+    // 24x scaling accounts for the 24x faster PIT clock.
+    // Looks like it's blinking at 1Hz, but I'm not pulling out
+    // my scope or stopwatch or anything.
+    Some(crate::Pit::new(
+        &pit,
+        timer_delay_microseconds.saturating_mul(24),
+    ))
+}