Because channels are written using a register's preferred word-sized slot, the 64-bit address already has the high-order bits in the preferred slot.
由于信道是通过寄存器单字大小的首选槽写入的，所以64位地址在首选槽内已经有了高阶位。
2
The effective address is, under the hood, always split into a pair of 32-bit registers; the high-order register is optional and if it's not specified, it is treated as zero.