diff --git a/kernel/src/arch/riscv/entry.rs b/kernel/src/arch/riscv/entry.rs
index 1c863a3..fe41b8c 100644
--- a/kernel/src/arch/riscv/entry.rs
+++ b/kernel/src/arch/riscv/entry.rs
@@ -16,7 +16,7 @@ unsafe extern "C" fn _start(hart_id: usize, fdt_addr: usize) -> ! {
     // we should be launched by OpenSBI and running is S-mode
 
     // 128 KiB stack for debugging only
-    const STACK_SIZE: usize = 4096 * 32;
+    const STACK_SIZE: usize = 4096 * 32; // at least 21, TODO: figure out why we need sooo much stack
     #[link_section = ".bss.boot_stack"]
     static mut STACK: [u8; STACK_SIZE] = [0u8; STACK_SIZE];
 
diff --git a/kernel/src/drivers/irq/plic.rs b/kernel/src/drivers/irq/plic.rs
index 3139224..2784b90 100644
--- a/kernel/src/drivers/irq/plic.rs
+++ b/kernel/src/drivers/irq/plic.rs
@@ -6,7 +6,7 @@ use fdt::{node::FdtNode, Fdt};
 use log::trace;
 use spin::Mutex;
 
-const IRQ_INVALID: usize = u32::MAX as usize;
+const IRQ_OCCUPIED: usize = u32::MAX as usize; // OpenSBI will rewrite IRQ_M_EXT to this value
 const IRQ_S_EXT: usize = 9;
 const IRQ_M_EXT: usize = 11;
 
@@ -62,7 +62,7 @@ impl Driver for IrqPlic {
             let phandle = ctx.phandle; // cpu intc
             let irq = ctx.interrupts().next().unwrap(); // IRQ_M_EXT/IRQ_S_EXT
 
-            if irq == IRQ_INVALID {
+            if irq == IRQ_OCCUPIED {
                 trace!("[IrqPlic] context {} taken by SBI", i);
                 continue;
             }
diff --git a/kernel/src/plat/irq.rs b/kernel/src/plat/irq.rs
index 39041ad..fe2a554 100644
--- a/kernel/src/plat/irq.rs
+++ b/kernel/src/plat/irq.rs
@@ -23,3 +23,12 @@ pub struct IrqManager {
     state:   [IrqState; IRQ_NUM],
 }
 
+impl IrqManager {
+    pub fn new() -> Self {
+        Self {
+            handler: core::array::from_fn::<_, IRQ_NUM, _>(|_| CapEntry::new(NullCap::mint())),
+            state:   [IrqState::Inactive; IRQ_NUM],
+        }
+    }
+
+    }