If write returned zero, register the channel for OP_WRITE, remember the buffer somehow, and keep selecting.

如果写返回零，OP _ WRITE注册通道，记得缓冲区，并保持选择。

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If the protocol stack wants to update a register value because a write register function was received a buffer with the new register values is passed to the callback function.

如果协议栈收到了一个写寄存器命令，将会执行寄存器更新操作，一个包含新寄存器数值的缓冲区会传给回调函数。

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