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Media Local Bus (MLB)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
27-29
27.4.3
System Memory Buffers
System software must define system memory buffers for each hardware channel, using the CCBCR
n
and
CNBCR
n
registers. Each system memory buffer can occupy as much as 64 KB and must be aligned on a
64 KB boundary; however, the system memory buffers are not required to be contiguous with each other.
Each of the system memory buffers can be configured for either multi-packet or single-packet buffering.
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.
System memory must accommodate situations in which the end of the buffer does not coincide with the
end of the current packet (e.g. asynchronous and control RX packets). This requires the system memory
buffers to allow overflow by the worst-case packet length.
System memory buffers are referred to as
Previous Buffer
,
Current Buffer
, and
Next Buffer
. The
Current
Buffer
is the system memory buffer the DMA Controller is currently processing and is defined by the
CCBCR
n
register. The status of the
Current Buffer
is reflected in CSCR
n
[STS[3:0]]. The
Previous Buffer
is the system memory buffer the DMA Controller completed processing prior to the
Current Buffer
. The
status of the
Previous Buffer
is reflected in CSCR
n
[STS[11:8]]. The
Next Buffer
is the system memory
buffer the DMA Controller begins processing after the
Current Buffer
. The
Next Buffer
is defined by the
CNBCR
n
register.
For Isochronous RX channels, the DMA Controller aligns incoming packets on a packet boundary in
system memory, dependent on the setting of CECR
n
[IPL[7:0]] and the arrival of the
IsoSyncByte
command.
MLB Logical Channel 4 Interrupt
101
CSCR4[20:31]
CECR4[9:15]
MLB Logical Channel 5 Interrupt
102
CSCR5[20:31]
CECR5[9:15]
MLB Logical Channel 6 Interrupt
103
CSCR6[20:31]
CECR6[9:15]
MLB Logical Channel 7 Interrupt
104
CSCR7[20:31]
CECR7[9:15]
MLB Logical Channel 8 Interrupt
105
CSCR8[20:31]
CECR8[9:15]
MLB Logical Channel 9 Interrupt
106
CSCR9[20:31]
CECR9[9:15]
MLB Logical Channel 10 Interrupt
107
CSCR10[20:31]
CECR10[9:15]
MLB Logical Channel 11 Interrupt
108
CSCR11[20:31]
CECR11[9:15]
MLB Logical Channel 12 Interrupt
109
CSCR12[20:31]
CECR12[9:15]
MLB Logical Channel 13 Interrupt
110
CSCR13[20:31]
CECR13[9:15]
MLB Logical Channel 14 Interrupt
111
CSCR14[20:31]
CECR14[9:15]
MLB Logical Channel 15 Interrupt
112
CSCR15[20:31]
CECR15[9:15]
Table 27-24. MLB Interrupts
Interrupt Name
PXN20
Interrupt Vector
Interrupt Flag Bits
Interrupt Mask Bits
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