3.4
Peripheral Servicing Example
3.4.1 Nonbursting Peripherals
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01E0 2000h
Peripheral Servicing Example
www.ti.com
The EDMA3 channel controller also services peripherals in the background of CPU operation, without
requiring any CPU intervention. Through proper initialization of the DMA channels, they can be configured
to continuously service on-chip and off-chip peripherals throughout the device operation. Each event
available to the EDMA3 has its own dedicated channel, and all channels operate simultaneously. The only
requirements are to use the proper channel for a particular transfer and to enable the channel event in the
event enable register (EER). When programming a DMA channel to service a peripheral, it is necessary to
know how data is to be presented to the ARM. Data is always provided with some kind of synchronization
event as either one element per event (nonbursting) or multiple elements per event (bursting).
Nonbursting peripherals include the on-chip audio serial port (ASP) and many external devices, such as
codecs. Regardless of the peripheral, the DMA channel configuration is the same.
The ASP transmit and receive data streams are treated independently by the EDMA3. The transmit and
receive data streams can have completely different counts, data sizes, and formats.
shows
servicing incoming ASP data.
To transfer the incoming data stream to its proper location in L2 memory, the DMA channel must be set
up for a 1D-to-1D transfer with A-synchronization. Since an event (REVT) is generated for every word as it
arrives, it is necessary to have the EDMA3 issue the transfer request for each element individually.
shows the parameters for this transfer. The source address of the DMA channel is set to the
data receive register (DRR) address for ASP, and the destination address is set to the start of the data
block in L2. Since the address of DRR is fixed, the source B index is cleared to 0 (no modification) and the
destination B index is set to 01b (increment).
Based on the premise that serial data is typically a high priority, the DMA channel should be programmed
to be on queue 0.
Figure 3-7. Servicing Incoming ASP Data Example
EDMA3 Transfer Examples
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