MSC8113 Reference Manual, Rev. 0
16-22
Freescale Semiconductor
Direct Memory Access (DMA) Controller
16.2.4.2 Cyclic Buffer
A cyclic buffer is a continuous buffer. When the buffer at the current address reaches zero, the
pointer jumps back to the base address and the buffer is executed again. An example cyclic buffer
is shown in Figure 16-17.
Table 16-2 lists the DCPRAM values for channel BD 4. A 0x200 byte block is read from address
0x1000, an interrupt is generated when the buffer size reaches zero, and the transfer restarts from
base address 0x1000
.
Figure 16-17. Cyclic Buffer
Table 16-2. DCPRAM Values for a Cyclic Buffer
BD
DCPRAM Parameters
Value
Description
4
BD_ADDR
0x1000
External memory buffer current address
BD_SIZE
0x200
Size of transfer left for this buffer
BD_ATTR
INTRPT 0x1
Generate an interrupt when the buffer ends
CYC 0x1
Reinitialize BD_ADDR to original value when the size
reaches zero
CONT
0x1
Continuous mode: the channel is not closed when the size
reaches zero
NO_INC
0x0
Increment address after request is serviced
NBD
0x4
When the size reaches zero, the next request calls buffer 4
TSZ 0x4
Maximum transfer size is one burst
RD 0x1
Read buffer
BD_BSIZE
0x200
Buffer base size of cyclic buffer
0x1000
0x11f8
Interrupt
.
.
.
BD 4
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