Freescale Semiconductor MSC8156 Evaluation Module MSC8156EVM MSC8156EVM Benutzerhandbuch

Freescale Semiconductor

  

14-19

There are two types of DMA arbitration: round-robin and early-deadline-serve-first (EDF). The 
type of arbitration is selected via the DGCR[AT] bit (see  Table 14-17, DMAGCR Field 
Descriptions, on page 14-31).

The round-robin arbitration between channels is a least recently used (LRU) schema. Following 
is a list of the arbitration parameters according to their weight:

„ DMA port. Each channel is assigned to one DMA port. Each time a channel request is 

serviced, the channels assigned to its port are masked for three clock cycles. When there 
are requesting channels for both ports, they are serviced intermittently.

„ Fixed-priority among round-robin groups. Each channel is assigned to one of the four 

priority groups as defined by the DCHCRx[RRPG] bit. Each priority group can contain 
from 0 (empty) to all 16 channels. Pending requests from the highest-priority group are 
serviced first.

Table 14-11.  Parameter Values for a Three-Dimensional Cyclic Buffer 

8

BD_ADDR 

0x1000

External memory buffer current address.

BD_MD_SIZE 

0x40

Size of transfer left for this buffer.

BD_MD_BSIZE

0x40

Buffer base size of continuous buffer.

BD_MD_ATTR

SST 

0x1

Generate interrupt when buffer ends.

CONT

0x1

Non-continuous mode: the channel closes when the size reaches 
zero.

CYC

0x1

Cyclic three dimensions.

BTSZ

0x5

Basic transfer size is 16 bytes.

BD

0x2

Buffer dimension is 3.

SSTD 

0x2

Interrupt issued at the end of the third dimension.

CONTD 

0x2

Cyclic three-dimensional buffer.

BD_MD_2D

M2D_COUNT

0x10

Second dimension iterations left.

M2D_BCOUNT

0x10

Second dimension base number of iterations.

M2D_OFFSET

0xF3C0

Second dimension offset between two consecutive iterations.

BD_MD_3D

M3D_COUNT

0x100

Third dimension iterations left.

M3D_BCOUNT

0x100

Third dimension base number of iterations.

M3D_OFFSET

–0xF3FB0

Third dimension offset between two consecutive iterations of two 
dimension buffers.

BD_MD_4D

M4D_COUNT

0

Fourth dimension iterations left.

M4D_OFFSET

–0xFBFB0

Fourth dimension offset between two consecutive iterations.