SPRUGZ8D Datasheet, PDF (2162/3016 Pages) Texas Instruments – Technical Reference Manual

Architecture
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Note that the CPU may 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 CPU) and the common interrupt line can be used. The
RRDY bit for receive and XRDY bit for transmit will indicate when the threshold values are reached. Also,
by reading the receive buffer status RBUFFSTAT_REG register and transmit buffer status
XBUFFSTAT_REG register the CPU may 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 CPU needs to read this data. Since no interrupt or
DMA request is asserted the only option in this case is to read the receive buffer status register value and
to transfer the remaining data without using the DMA or interrupt indication.
17.2.5 Multichannel Selection Modes
17.2.5.1 Channels, Blocks, and Partitions
A McBSP channel is a time slot for shifting in/out the bits of one serial word. The McBSP 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 8 blocks that each contains 16 contiguous channels:
Block 0: Channels 0–15
Block 1: Channels 16–31
Block 2: Channels 32–47
Block 3: Channels 48–63
Table 17-3. Channels, Block, Partitions
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 2–partition mode,
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. For
example, it is possible to use two receive partitions (A and B) and eight transmit partitions (A–H).
17.2.5.2 Multichannel Selection
When a McBSP uses a time–division multiplexed (TDM) data stream while communicating with other
McBSPs or serial devices, the McBSP 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 has one receive multichannel selection mode and three transmit multichannel selection
modes.
17.2.5.3 Configuring a Frame for Multichannel Selection
Before you enable a multichannel selection mode, make sure you properly configure the data frame:
• Select a single–phase frame (RCR2_REG[15] register RPHASE bit and XCR2_REG[15] register
XPHASE bit = 0). Each frame represents a TDM data stream.
• Set a frame length (in RCR1_REG[14:8] register RFRLEN1 bit field and in XCR1_REG[14:8] register
XFRLEN1 bit field) that includes the highest–numbered channel to be used. For example, if you plan to
use channels 0, 15, and 39 for reception, the receive frame length must be at least 40 (RFRLEN1 =
39). If XFRLEN1 = 39 in this case, the receiver creates 40 time slots per frame but only receives data
during time slots 0, 15, and 39 of each frame.
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Multichannel Buffered Serial Port (McBSP)
SPRUGZ8D – 14 November 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated
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