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Media Local Bus (MLB)
PXN20 Microcontroller Reference Manual, Rev. 1
27-32
Freescale Semiconductor
27.4.6
DMA Controller (Ping-Pong Buffering)
Using the MLB DMA Controller with ping-pong buffering dictates a particular method used for
transferring data between hardware channels and system memory. When the MLB hardware channels are
configured in this mode, the CCBCR
n
and CNBCR
n
registers are used to configure and monitor the
system memory
Current Buffer
and
Next Buffer
, respectively.
Channels use ping-pong buffering when CECR
n
[MDS[1:0]] = 00. The
Current Buffer
and
Next Buffer
are
independent system memory buffers, which allow hardware to support the ping-pong buffering. Each is
addressed using two 16-bit address pointers, as follows:
•
Buffer Start Address (CNBCR
n
[BSA]) – defines the beginning address of the
Next Buffer
in
system memory
•
Buffer End Address (CNBCR
n
[BEA]) – determines the end of the
Next Buffer
in system memory
•
Buffer Current Address (CCBCR
n
[BCA]) – defines the beginning of the
Current Buffer
in system
memory
•
Buffer Final Address (CCBCR
n
[BFA]) – defines the end of the
Current Buffer
in system memory
27.4.6.1
Asynchronous and Control Packet Handling
The
Current Buffer
and
Next Buffer
can be configured for either multi-packet or single-packet buffering,
when receiving and transmitting asynchronous and control packet data. Multi-packet buffering allows the
system to reduce the interrupt load at the expense of larger system memory buffers. Single-packet
buffering allows system memory buffer size to be reduced at the expense of increasing the interrupt rate.
An example of multi-packet buffering for asynchronous and control channels is provided in
Содержание PXN2020
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Страница 42: ...PXN20 Microcontroller Reference Manual Rev 1 lxiv Freescale Semiconductor...
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