When an SPU tries to read from an empty mailbox, it will stop execution until some value is written to its memory-mapped register.

当spu视图从一个空的邮箱中读取信息时，它会停止执行，直到有值写入自己的内存映射寄存器中为止。

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The ppe does this through memory-mapped register access from kernel mode, while the SPE writes to its DMA channels from code running on the SPU.

PPE可以通过在内核模式中使用内存映射寄存器来发起dma传输，而SPE则可以使用在SPU上运行的代码来写入dma通道。

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When the ppe wants to access the mailbox, it needs to have access to the memory-mapped register space, which is normally only available to kernel space.

当PPE希望访问邮箱时，它需要能够访问内存映射的寄存器空间，后者通常只对于内核空间来说是可用的。

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