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    //! Implementation of [`TaskContext`]

    /// Task Context
    #[derive(Copy, Clone)]
    #[repr(C)]
    pub struct TaskContext {
        /// return address ( e.g. __restore ) of __switch ASM function
        ra: usize,
        /// kernel stack pointer of app
        sp: usize,
        /// callee saved registers:  s 0..11
        s: [usize; 12],
    }

    impl TaskContext {
        /// init task context
        pub fn zero_init() -> Self {
            Self {
                ra: 0,
                sp: 0,
                s: [0; 12],
            }
        }

        /// set task context {__restore ASM funciton, kernel stack, s_0..12 }
        pub fn goto_restore(kstack_ptr: usize) -> Self {
            extern "C" {
                fn __restore();
            }
            Self {
                ra: __restore as usize,
                sp: kstack_ptr,
                s: [0; 12],
            }
        }
    }