A coroutine call instruction.The instruction pops the top of stack into temporary register, pushes program counter onto the stack, and then puts the saved top of stack in the program counter. 一种协同程序访问指令，该指令把栈顶弹入临时寄存器，把程序计数器推入栈内，然后把保存的栈顶内容存入到程序计数器内。
Coroutines are computer program components that generalize subroutines for nonpreemptive multitasking, by allowing multiple entry points for suspending and resuming execution at certain locations. Coroutines are well-suited for implementing more familiar program components such as cooperative tasks, exceptions, event loop, iterators, infinite lists and pipes.