Channels are unidirectional, function-specific registers or queues. They are the primary means of communication between an SPE’s SPU and its MFC, which in turn mediates communication with the PPE, other SPEs, and other devices. These other devices use MMIO registers in the destination SPE to transfer information on the channel interface of that destination SPE.
Specific channels have read or write properties, and blocking or nonblocking properties. Software on the SPU uses channel commands to enqueue DMA commands, query DMA and processor status, perform MFC synchronization, access auxiliary resources such as the decrementer (timer), and perform interprocessor-communication via mailboxes and signal-notification.