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Media Local Bus (MLB)
PXN20 Microcontroller Reference Manual, Rev. 1
27-36
Freescale Semiconductor
Figure 27-20. Isochronous/Synchronous Data Buffering Examples
For reception or transmission of isochronous data, single-packet and multi-packet buffering is handled in
the same manner. Since isochronous channels have a fixed packet length (determined by CECR
n
[IPL]),
software should set the system memory buffer length as an even multiple of CECR
n
[IPL] for multi-packet
buffering and equal to CECR
n
[IPL] for single-packet buffering. It is assumed that all isochronous packets
in the system are of the same length, with the minimum supported length being 5 bytes.
For reception or transmission of synchronous data, the concept of multi-packet or single-packet buffering
is not applicable since synchronous data has no packet format. As a result, CCBCR
n
[BFA] always
indicates the end address of the
Current Buffer
for synchronous channels.
27.4.7
DMA Controller (Circular Buffering)
Logical channels can be programmed to operate using circular buffering by programming
CECR
n
[MDS[1:0]] = 01. It is recommended that circular buffering be used with synchronous channels
only (CECR
n
[CT[1:0]] = 00). Logical channels configured for transmitting or receiving other types of
data (e.g. asynchronous, control, or isochronous) should not use circular buffering.
In contrast ping-pong buffering, this mode effectively uses a single, circular system memory buffer to
process channel data. Software must program the beginning and ending address of the circular buffer in
the CNBCR
n
[BSA] and CNBCR
n
[BEA] fields. For proper operation, software must not change the
addresses in CNBCR
n
[BSA] and CNBCR
n
[BEA] once buffer processing has started.
Isochronous
BS
BD
BCA
BFA
BEA
BSA
BCA
Note 3
Note 1
Note 4
Note 2
Legend
= 16-bit address pointer
= channel interrupt
(Shows RX/TX handling of Isochronous/Synchronous Data using the Current Buffer)
Isochronous/Synchronous Data Buffering Examples
(First Packet)
Packet 1
Isochronous
Packet 2
Isochronous
Packet 3
Isochronous
(Last Packet)
Packet N
Synchronous
Data
Current Buffer
for Synchronous
channel
Current Buffer
for Isochronous
channel
Summary of Contents for PXN2020
Page 1: ...PXN20 Microcontroller Reference Manual Devices Supported PXN2020 PXN2120 PXN20RM Rev 1 06 2011...
Page 42: ...PXN20 Microcontroller Reference Manual Rev 1 lxiv Freescale Semiconductor...
Page 64: ...Introduction PXN20 Microcontroller Reference Manual Rev 1 1 22 Freescale Semiconductor...
Page 112: ...Signal Description PXN20 Microcontroller Reference Manual Rev 1 3 44 Freescale Semiconductor...
Page 118: ...Resets PXN20 Microcontroller Reference Manual Rev 1 4 6 Freescale Semiconductor...
Page 372: ...e200z6 Core Z6 PXN20 Microcontroller Reference Manual Rev 1 13 8 Freescale Semiconductor...
Page 412: ...e200z0 Core Z0 PXN20 Microcontroller Reference Manual Rev 1 14 14 Freescale Semiconductor...
Page 821: ...Media Local Bus MLB PXN20 Microcontroller Reference Manual Rev 1 Freescale Semiconductor 27 49...
Page 822: ...Media Local Bus MLB PXN20 Microcontroller Reference Manual Rev 1 27 50 Freescale Semiconductor...
Page 1376: ...Memory Map PXN20 Microcontroller Reference Manual Rev 1 A 118 Freescale Semiconductor...