Media Local Bus (MLB)
PXN20 Microcontroller Reference Manual, Rev. 1
27-30 Freescale Semiconductor
27.4.4 Local Channel Buffer RAM
A single-port RAM is used to implement the memory space for local channel buffering. The size of the
RAM is 2k x 36-bits (1 quadlet of data; 4-bit tag). The initial start address and depth values for the logical
channels buffered in the RAM are controlled via the LCBCRn. After reset, the initial settings can be
overwritten by software.
See Figure 27-17 for more information on using the LCBCRn to configure the local RAM buffer.
Figure 27-17. Programming Example for LCBCRn
27.4.4.1 Local Buffer Start Address
The initial buffer start address of each local channel buffer is defined by the default (after reset) start
address of each local channel buffer (LCBCRn[SA[8:0]]). The start address is the location of the beginning
of the buffer in the local buffer RAM. Software may change the start address of each local channel buffer
after reset by writing to LCBCRn[SA[8:0]] directly.
27.4.4.2 Local Channel Buffer Depth
The initial buffer depth of each local channel buffer is configured by the default (after reset) depth of each
local channel buffer (LCBCRn[BD[8:0]]) in quadlets. The buffer depth should be set based on the
worst-case DMA interface read/write latency. Software may change the depth of each local channel buffer
after reset by writing to LCBCRn[BD[8:0]] directly.
Local Channel Buffer 0
LCBCR0.BD
LCBCR0.SA
Local Channel Buffer 2
LCBCR2.BD
LCBCR2.SA
Local Channel Buffer 1
LCBCR1.BD
LCBCR1.SA
0
2048
36 bits
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