DMA Controller

5

This chapter describes the on-chip DMA controller (DMAC) for the PXA255 processor. The DMAC transfers data to and from main memory in response to requests generated by internal and external peripherals. The peripherals do not directly supply addresses and commands to the memory system. The DMAC has 16 DMA channels, 0 through 15, and every DMA request from the peripheral generates at least one memory bus cycle.

5.1DMA Description

The DMAC supports only flow-through transfers.

Flow-through data passes through the DMAC before the data is latched by the destination in its buffers/memory. This DMAC can perform memory-to-memory moves with flow-through transfers.

Figure 5-1provides an overview of the DMAC. Table 5-1provides a list of the DMAC signals and descriptions.

Figure 5-1. DMAC Block Diagram

 

 

Memory Controller

 

 

 

System Bus (internal)

 

 

Control Registers

DMA Controller

 

 

 

16 DMA Channels

 

 

 

Channel 15

 

DREQ[1:0]

DCSR0

 

 

(external)

Channel 0

 

 

 

 

 

DDADR0

 

 

DRCMR0

DSADR0

DMA_IRQ

 

(internal)

 

 

 

 

DTADR0

 

PREQ[37:0]

 

DCMD0

 

(internal)

DINT

 

 

 

 

Peripheral Bus

 

 

 

(internal)

 

Intel® PXA255 Processor Developer’s Manual

 

5-1

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Intel PXA255 manual DMA Description, Dmac Block Diagram