use core::arch::asm;

const SYSCALL_WRITE: usize = 64;
const SYSCALL_EXIT: usize = 93;
const SYSCALL_YIELD: usize = 124;
const SYSCALL_GET_TIME: usize = 169;


fn syscall(id: usize, args: [usize; 3]) -> isize {
    let mut ret: isize;
    unsafe {
        // a0寄存器同时作为输入参数和输出参数, {in_var} => {out_var}
        asm!(
        "ecall",
        inlateout("x10") args[0] => ret,
        in("x11") args[1],
        in("x12") args[2],
        in("x17") id
        );
    }
    ret
}


pub fn sys_write(fd: usize, buffer: &[u8]) -> isize {
    syscall(SYSCALL_WRITE, [fd, buffer.as_ptr() as usize, buffer.len()])
}

pub fn sys_exit(exit_code: i32) -> isize {
    syscall(SYSCALL_EXIT, [exit_code as usize, 0, 0])
}

pub fn sys_yield() {
    syscall(SYSCALL_YIELD, [0, 0, 0]);
}

pub fn sys_get_time() -> isize {
    syscall(SYSCALL_GET_TIME, [0, 0, 0])
}


