feat: add idle thread

kernel/src/arch/riscv/trap.rs

@@ -2,7 +2,6 @@ use crate::entry::HART_ID;
 use crate::plat::console::CONSOLE;
 use crate::plat::timer::{Timer, TimerOps};
 use crate::plat::trap::{Trap, TrapContextOps, TrapOps};
-use crate::scheduler::SCHEDULER;
 use log::trace;
 use riscv::register::scause::{Exception as E, Interrupt as I, Trap as T};
 use riscv::register::stvec::TrapMode;
@@ -17,54 +16,10 @@ extern "C" {
 
 #[no_mangle]
 extern "C" fn kernel_trap_handler(tf: &mut TrapContext) {
+    // No trap in kernel, except from IDLE thread
     // TODO: Replace CONSOLE Mutex to ReentrantLock
     unsafe { CONSOLE.force_unlock() }
-    trap_handler(tf, true)
-}
-
-fn trap_handler(tf: &mut TrapContext, from_kernel: bool) {
-    let scause = riscv::register::scause::read();
-    trace!("[Trap] cpu@{} scause: {:?}", HART_ID.get(), scause.cause());
-
-    macro_rules! panic_fatal {
-        ($msg:expr) => {
-            panic!(
-                "[Trap] {}, scause: {:?}, bits: {:#x}, sepc: {:#x}, stval: {:#x}",
-                $msg,
-                scause.cause(),
-                scause.bits(),
-                tf.sepc,
-                riscv::register::stval::read()
-            )
-        };
-    }
-
-    match scause.cause() {
-        T::Interrupt(I::SupervisorTimer) => {
-            Timer::do_tick();
-
-            if !from_kernel {
-                SCHEDULER.schedule()
-            }
-        },
-        T::Exception(E::UserEnvCall) => {
-            // TODO: handle syscall
-            tf.sepc += 4;
-        },
-        T::Interrupt(I::SupervisorExternal) => {
-            // TODO: handle external interrupt, e.g. plic
-        },
-        T::Exception(E::InstructionPageFault) | T::Exception(E::LoadPageFault) | T::Exception(E::StorePageFault) => {
-            if from_kernel {
-                panic_fatal!("Page Fault in Kernel");
-            }
-            // TODO: handle page fault
-        },
-        _ => panic_fatal!("Unhandled Trap"),
-    }
-
-    Timer::set_next();
-    trace!("[Trap] exiting...");
+    tf.trap_handler(true);
 }
 
 impl TrapOps for Trap {
@@ -76,13 +31,70 @@ impl TrapOps for Trap {
     }
 }
 
+#[naked]
+extern "C" fn idle_thread() {
+    unsafe {
+        core::arch::asm!(
+            "
+                1: wfi
+                   j   1b
+            ",
+            options(noreturn)
+        )
+    };
+}
+
 impl TrapContextOps for TrapContext {
     fn restore(&mut self) {
         unsafe { switch_to_user(self) }
     }
+
+    fn configure_idle_thread(&mut self) {
+        self.sepc = idle_thread as usize;
+        self.sstatus = (1 << 5) | (1 << 8); // SPIE + SPP
+    }
+
+    fn trap_handler(&mut self, from_kernel: bool) {
+        let scause = riscv::register::scause::read();
+        trace!("[Trap] cpu@{} scause: {:?}", HART_ID.get(), scause.cause());
+
+        macro_rules! panic_fatal {
+            ($msg:expr) => {
+                panic!(
+                    "[Trap] {}, scause: {:?}, bits: {:#x}, sepc: {:#x}, stval: {:#x}",
+                    $msg,
+                    scause.cause(),
+                    scause.bits(),
+                    self.sepc,
+                    riscv::register::stval::read()
+                )
+            };
+        }
+
+        match scause.cause() {
+            T::Interrupt(I::SupervisorTimer) => Timer::do_tick(),
+            T::Exception(E::UserEnvCall) => {
+                // TODO: handle syscall
+                self.sepc += 4;
+            },
+            T::Interrupt(I::SupervisorExternal) => {
+                // TODO: handle external interrupt, e.g. plic
+            },
+            T::Exception(E::InstructionPageFault) | T::Exception(E::LoadPageFault) | T::Exception(E::StorePageFault) => {
+                if from_kernel {
+                    panic_fatal!("Page Fault in Kernel");
+                }
+                // TODO: handle page fault
+            },
+            _ => panic_fatal!("Unhandled Trap"),
+        }
+
+        Timer::set_next();
+        trace!("[Trap] exiting...");
+    }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Default)]
 #[repr(C)]
 pub struct GeneralRegs {
     pub ra:  usize,
@@ -118,7 +130,7 @@ pub struct GeneralRegs {
     pub t6:  usize,
 }
 
-#[derive(Debug)]
+#[derive(Debug, Default)]
 #[repr(C)]
 pub struct TrapContext {
     // [0:30] GPRs exclude zero

kernel/src/plat/trap.rs

@@ -6,4 +6,6 @@ pub trait TrapOps {
 
 pub trait TrapContextOps {
     fn restore(&mut self);
+    fn configure_idle_thread(&mut self);
+    fn trap_handler(&mut self, from_kernel: bool);
 }