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The SPP DMA Controller Module (SPP_DMA2)

MAC7200 Microcontroller Family Reference Manual, Rev. 2

202

Freescale Semiconductor

•

32 bytes of data registers, used as temporary storage to support burst transfers

Throughout this document, n is used to reference the channel number. Additionally, data sizes are defined

as byte (8-bit), halfword (16-bit), word (32-bit) and doubleword (64-bit).

12.2.2

Features

The DMA module supports the following features:

•

All data movement via dual-address transfers: read from source, write to destination

— Programmable source, destination addresses, transfer size, plus support for enhanced

addressing modes

•

Transfer control descriptor organized to support two-deep, nested transfer operations

—An inner data transfer loop defined by a “minor” byte transfer count

—An outer data transfer loop defined by a “major” iteration count

•

Channel service request via one of three methods:

— Explicit software initiation

— Initiation via a channel-to-channel linking mechanism for continuous transfers

— Independent channel linking at end of minor loop and/or major loop

— Peripheral-paced hardware requests (one per channel)

— For all three methods, one service request per execution of the minor loop is required

•

Support for fixed-priority and round-robin channel arbitration

•

Channel completion reported via optional interrupt requests

— One interrupt per channel, optionally asserted at completion of major iteration count

— Error terminations are optionally enabled per channel, and logically summed together to form

a small number of error interrupt outputs

•

Optional support for scatter/gather DMAprocessing

The structure of the transfer control descriptor is fundamental to the operation of the DMA module. It is

defined below in a ‘C‘ pseudo-code specification:

NOTE

To compile these structures, change any periods ’.’ in the variable name to

underscores ’_’.

typedef union {

struct {

/* citer.e_link = 1 */

unsigned short citer.linkch:6;

/* link channel number, */

unsigned short citer:9;

/* current (“major”) iteration count */

} minor_link_enabled;

/* channel link at end of the minor loop */

struct {

/* citer.e_link = 0 */

unsigned short citer:15;

/* current (“major”) iteration count */

} minor_link_disabled;

/* no linking at end of the minor loop */

} t_minor_link_citer;

typedef union {

struct {

/* biter.e_link = 1 */

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