Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 587

Chapter 19
SDMA Channels and IDMA Emulation
The CPM controls four physical serial DMA (SDMA) channels on the MPC885 for the CP, the first FEC,
the second FEC, and the security engine. Using a physical channel, the CP implements twenty-two virtual
SDMA channels, each dedicated to a serial controller transmitter or receiver—eight for the USB, six for
2
the full-duplex SCCs, and the remaining eight for the SPI, I C, and the two SMCs. The CPM also emulates
two general-purpose independent DMA (IDMA) channels for memory/memory and peripheral/memory
transfers using the two physical SDMA channels.
19.1 SDMA Channels
Data from the CP, FECs, and security engine can be routed to external memory (path 1) or the internal
dual-port RAM (path 2), as shown in Figure 19-1. On a path 1 access, the SDMA channel must acquire
both the U-bus and the external system bus. On a path 2 access, the data transfer occurs only on the U-bus,
independent of the external system bus unless the SIU is configured in show-cycles mode. Thus, in normal
operation, U-bus transfers occur simultaneously with external system bus operations. The description is
the same for the FECs and the security engine.
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor 19-1