Public Version
McBSP Functional Description
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NOTE:
The MPU/IVA2.2 subsystem can decide not to use the DMA to transfer the data. In this
case, the DMA must be disabled (or the DMA request can be ignored by MPU/IVA2.2
subsystem) and the common interrupt line (McBSPi_IRQ) can be used. The
McBSPi.
[1] RRDY bit for receive and
[1] XRDY bit for transmit will indicate when the threshold
values are reached. Also, by reading the receive buffer status
McBSPi.
register and transmit buffer status
register, the MPU/IVA2.2 subsystem can decide to
transfer data even if the threshold is not reached. This mechanism is useful on the last
transfer on receive side when the threshold value is bigger than the occupied locations inside
the receive buffer and the MPU/IVA2.2 subsystem needs to read this data. Since no interrupt
or DMA request is asserted the only option in this case is to read the RB status register
value and to transfer the remaining data without using the DMA or interrupt indication.
21.4.6 Multichannel Selection Modes
21.4.6.1 Channels, Blocks, and Partitions
A McBSP channel is a time slot for shifting in/out the bits of one serial word. The McBSP module supports
up to 128 channels for reception and 128 channels for transmission. In the receiver and in the transmitter,
the 128 available channels are divided into eight blocks that contain 16 contiguous channels each:
•
Block 0: Channels 0–15
•
Block 1: Channels 16–31
•
Block 2: Channels 32–47
•
Block 3: Channels 48–63
•
Block 4: Channels 64–79
•
Block 5: Channels 80–95
•
Block 6: Channels 96–111
•
Block 7: Channels 112–127
The blocks are assigned to partitions according to the selected partition mode. In the two-partition mode
described in
, you assign one even-numbered block (0, 2, 4, or 6) to partition A and one
odd-numbered block (1, 3, 5, or 7) to partition B. In the 8-partition mode
, blocks 0 through
7 are automatically assigned to partitions A through H, respectively.
The number of partitions for reception and the number of partitions for transmission are independent of
each other. For example, it is possible to use two receive partitions (A and B) and eight transmit partitions
(A–H).
21.4.6.2 Multichannel Selection
When a McBSP module uses a time-division multiplexed (TDM) data stream while communicating with
other McBSP modules or serial devices, the McBSP module may need to receive and/or transmit on only
a few channels. To save memory and bus bandwidth, you can use a multichannel selection mode to
prevent data flow in some of the channels.
Each channel partition has a dedicated channel enable register. If the appropriate multichannel selection
mode is on, each bit in the register controls whether data flow is allowed or prevented in one of the
channels that is assigned to that partition.
The McBSP module has one receive multichannel selection mode
, and three transmit
multichannel selection modes
21.4.6.3 Configuring a Frame for Multichannel Selection
Before enabling a multichannel selection mode, make sure you properly configure the data frame:
•
Select a single-phase frame (McBSPi.
[15] RPHASE bit and
[15] XPHASE bit = 0). Each frame represents a TDM data stream.
3114
Multi-Channel Buffered Serial Port
SWPU177N – December 2009 – Revised November 2010
Copyright © 2009–2010, Texas Instruments Incorporated