Enable cache for AST10x0 performance

target/ast10x0/BUILD.bazel

@@ -81,6 +81,7 @@ rust_library(
     tags = ["kernel"],
     target_compatible_with = TARGET_COMPATIBLE_WITH,
     deps = [
+        "@ast1060_pac",
         "@pigweed//pw_kernel/arch/arm_cortex_m:arch_arm_cortex_m",
         "@pigweed//pw_kernel/kernel",
         "@pigweed//pw_status/rust:pw_status",

target/ast10x0/entry.rs

@@ -10,11 +10,14 @@ use arch_arm_cortex_m::Arch;
 #[cfg(feature = "jtag-halt")]
 use core::ptr::{self, addr_of};
 
-/// Pre-kernel hardware initialization
-/// Runs before RAM is initialized, before main()
 #[cfg(feature = "jtag-halt")]
-#[cortex_m_rt::pre_init]
-unsafe fn pre_kernel_init() {
+/// Enable ARM JTAG pins via SCU pinmux and halt waiting for a debugger.
+///
+/// # Safety
+/// Caller must have exclusive early-boot ownership of SCU MMIO and must have
+/// already unlocked SCU write protection (write `0x1688_A8A8` to `SCU000`);
+/// otherwise the `SCU41C` pinmux write is silently dropped.
+unsafe fn jtag_init() {
     // Enable JTAG pins via SCU pinmux - must happen very early
     // Scu::steal() is safe here: it's a zero-sized type with no RAM allocation
     let scu = unsafe { ast1060_pac::Scu::steal() };
@@ -43,6 +46,48 @@ unsafe fn pre_kernel_init() {
         }
     }
 }
+/// Configure and enable the AST10x0 instruction/data cache.
+///
+/// Sequence: disable cache, program the cacheable area, invalidate, re-enable.
+///
+/// # Safety
+/// Caller must have exclusive early-boot ownership of SCU MMIO and must have
+/// already unlocked SCU write protection.
+unsafe fn init_cache() {
+    // SAFETY: see function-level safety contract.
+    let scu = unsafe { &*ast1060_pac::Scu::ptr() };
+
+    // Disable cache.
+    scu.scua58().write(|w| unsafe { w.bits(0) });
+
+    // Configure cache area.
+    scu.scua50().write(|w| unsafe { w.bits(0x000f_ffff) });
+
+    // Invalidate cache.
+    scu.scua54().write(|w| unsafe { w.bits(0x8660_0000) });
+
+    // Re-enable cache.
+    scu.scua58().write(|w| unsafe { w.bits(1) });
+}
+
+// Pre-kernel hardware initialization
+/// Runs before RAM is initialized, before main()
+#[cortex_m_rt::pre_init]
+unsafe fn pre_init() {
+    // SAFETY: pre-init has exclusive early-boot ownership of SCU MMIO.
+    let scu = unsafe { &*ast1060_pac::Scu::ptr() };
+
+    // Unlock SCU write-protected registers.
+    scu.scu000().write(|w| unsafe { w.bits(0x1688_A8A8) });
+
+    #[cfg(feature = "jtag-halt")]
+    jtag_init();
+
+    // SAFETY: SCU is unlocked above; pre-init has exclusive ownership.
+    unsafe { init_cache() };
+}
+
+
 
 #[unsafe(no_mangle)]
 #[allow(non_snake_case)]