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4-6 Optimizing DSP56300/DSP56600 Applications MOTOROLA

Using the DMA

Servicing a Peripheral

;DAM[5:3]101 destination address post-increment

;DAM[2:0]000 source address: 2D with offset register 0

;DS[3:2]01 transfer destination: y memory.

;DS[1:0]01 transfer source: y memory.

movep #$580285,x:M_DCR0;load control register.

;============ main program

...

bset #23,x:M_DCR0 ;trigger transfer

...

;============ interrupt definition

org p:I_DMA0

jsr <USE_COMPACT_DATA

4.4 SERVICING A PERIPHERAL

DMA transfers can be triggered by peripherals and can transfer data

to and from them, thus giving the user a powerful alternative for

driving peripherals. Examples for interrupt-driven core handling

were given earlier in Section 3. Using the DMA to handle

peripheral requests has the following advantages:

1. Saves core MIPS because the DMA is triggered

independently and transfers the data in parallel to the core

2. Frees core address registers that previously had to be

reserved as pointers to the data buffers to keep them

available for processing a fast interrupt

3. Decreases the latency between peripheral triggering and

actual handling by using the DMA (under the same

circumstances, i.e., no other triggers/interrupts with higher

priorities)

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Motorola DSP56305 Manuale Utente Pagina 55