Freescale Semiconductor MSC8156 Evaluation Module MSC8156EVM MSC8156EVM Manual Do Utilizador

Freescale Semiconductor

  

14-7

In an incremental buffer, a data transfer starts at the buffer base address and continues until all 
data is transferred. An interrupt is generated each time BD_SIZE reaches zero. 
BD_ATTR[CONT] = 1, so the channel does not close when BD_SIZE reaches zero. 
BD_ATTR[CYC] = 0, signifying sequential addressing. NBD points to the buffer itself. Figure 
14-5 shows an example incremental buffer.

Figure 14-5.  One-Dimensional Incremental Buffer

Table 14-4 lists the channel parameter values for an incremental buffer (BD0). Blocks of 0x100 
bytes are read, starting at address 0x1000, and an interrupt is generated every 0x100 bytes. The 
mode is continuous and addressing is sequential. Be aware that in an incremental buffer, memory 
can be corrupted because of overwriting. 

Table 14-4.  Channel Parameter Values for an Incremental Buffer 

0

BD_ADDR 

0x1000

External memory buffer current address.

BD_SIZE 

0x100

Size of transfer left for this buffer.

BD_BSIZE 

0x100

Buffer base size of cyclic buffer.

BD_ATTR 

SST 

0x1

Generate interrupt when buffer ends.

CONT 

0x1

Continuous mode. Do not close the buffer when size reaches zero.

CYC

0x0

Increment BD_ADDRESS when size reaches zero.

NBD

0x0

Next request calls buffer 0 when size reaches zero.

0x1000

0x10F8

0x1200

0x12F8

Interrupt

0x1100

0x11F8

Interrupt

Interrupt

BD0