NXP Semiconductors PXN2020 - 27.4.8 Streaming Channel Frame Synchronization

Media Local Bus (MLB)
PXN20 Microcontroller Reference Manual, Rev. 1
27-38 Freescale Semiconductor
27.4.8 Streaming Channel Frame Synchronization
Certain types of streaming applications require data to be synchronous with the MLB frame, including:
stereo, 5.1 audio, and Generic Synchronous Packet Format (GSPF) DTCP. The MLB
Streaming Channel Frame Synchronization feature provides this option.
For example, 24-bit stereo channels require two MLB physical channels (PC) to transmit left (0xLLLLLn)
and right (0xRRRRRn) speaker data. Assuming the MLB Controller allocates Physical Channel 1 (PC1)
and Physical Channel 2 (PC2) to this stereo channel, the data would be synchronized to the MLB frame as
shown in Table 27-25.
Without frame synchronization, the MLB may begin transmitting or receiving data that is not aligned with
the MLB frame. Misalignment, as depicted in Table 27-26, may result in data corruption.
The MLB supports Streaming Channel Frame Synchronization as a programmable option for each logical
channel configured for synchronous dataflow. System software can enable the frame synchronization
feature for a synchronous logical channel by setting CECHRn[FSE]. When enabled, the synchronous
logical channel begins transmitting and receiving data only at a MLB frame boundary.
When the loss of MLB frame synchronization occurs, the MLB detects it and optionally notifies system
software via a maskable channel interrupt. In order to use this option, system software must:
• program CECRn[FSPC[4:0]] with the expected number of physical channels per frame for the
logical channel, and
• unmask the CSCRn[STS[6]] bit by setting CECRn[MLFS] to 0.
A channel interrupt is generated when the actual number of physical channels detected during a MLB
frame does not match the expected value. An additional channel interrupt is generated if the local channel
buffer overflows (for RX channels) or underflows (for TX channels).
Table 27-25. Example of 24-bit Stereo Data Synchronous to 256 Fs MediaLB frame
Frame PC=0 PC=1 PC=2 PC=3 PC=4 PC=5 PC=6 PC=7
n=0
0xLLLL_LLRR 0xRRRR_xxxx
n=1
0xLLLL_LLRR 0xRRRR_xxxx
n=2
0xLLLL_LLRR 0xRRRR_xxxx
n=3
0xLLLL_LLRR 0xRRRR_xxxx
Table 27-26. Example of 24-bit Stereo Data Asynchronous to 256 Fs MediaLB frame
Frame PC=0 PC=1 PC=2 PC=3 PC=4 PC=5 PC=6 PC=7
n=0
0xLLLL_LLRR
n=1
0xRRRR_xxxx 0xLLLL_LLRR
n=2
0xRRRR_xxxx 0xLLLL_LLRR
n=3
0xRRRR_xxxx 0xLLLL_LLRR