feat(hal/imx8mn): added test code to test armv8 exception handling impl

Author: nihalpasham

boards/bootloaders/imx8mn/imx8mn.bin

@@ -18,7 +18,7 @@ global_asm!(include_str!("entry.s"));
 ///
 #[no_mangle]
 pub unsafe extern "C" fn _start_rust() -> ! {
-    // disable mmu, i and d caching
+    // disable i and d caching, mmu is already disabled.
     memory::mmu::mmu().disable_mmu_and_caching();
     // set the vector base address for excpetion handlers
     exception::exception::handling_init();

boards/bootloaders/imx8mn/src/boot.rs

@@ -71,9 +71,8 @@ fn kernel_main() -> ! {
     }
 
     // info!("");
-    // info!("Trying to read from address 8 GiB...");
-    // let mut big_addr: u64 = 8 * 1024 * 1024 * 1024;
-    // unsafe { core::ptr::read_volatile(big_addr as *mut u64) };
+    // info!("Trying to read from non-existent OCRAM addresss 0x980000...");
+    // unsafe { core::ptr::read_volatile(0x980000 as *mut u64) };
 
     wait_forever()
 }

boards/bootloaders/imx8mn/src/main.rs

@@ -8,6 +8,8 @@ use tock_registers::{
     registers::InMemoryRegister,
 };
 
+pub use aarch64_cpu::registers::VBAR_EL3;
+
 // Assembly counterpart to this file.
 global_asm!(include_str!("exception.s"));
 
@@ -270,4 +272,5 @@ pub unsafe fn handling_init() {
 
     // Force VBAR update to complete before next instruction.
     barrier::isb(barrier::SY);
+    
 }