Motorola MPC860 PowerQUICC, User Manual

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MOTOROLA Chapter 20. SDMA Channels and IDMA Emulation 20-1
Chapter 20
SDMA Channels and IDMA Emulation
200
200
The CPM controls two physical serial DMA (SDMA) channels on the MPC860. Using the
two physical channels, the CP implements sixteen virtual SDMA channels, each dedicated
to a serial controller transmitter or receiverÑeight for the full-duplex SCCs, and the
remaining eight for the SPI, I
2
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.
20.1 SDMA Channels
Data from the SCCs, SMCs, SPI, and I
2
C can be routed to external memory (path 1) or the
internal dual-port RAM (path 2), as shown in Figure 20-1. 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 conÞgured in show-cycles mode. Thus, in normal operation, U-bus transfers occur
simultaneously with external system bus operations.
Figure 20-1. MPC860 SDMA Data Paths
SCC1 SCC2 SCC3 SCC4 SMC1 SMC2 SPI I
2
C
System Bus
System
Interface
Unit
(SIU)
External
ROM
External
RAM
PowerPC
Core
Dual-Port
RAM
Communications
Processor
(CP)
SDMA
2
1
Internal U-Bus