SAM4L Datasheet, PDF (314/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
16.4.4
Peripheral Events
The PDCA peripheral events are connected via the Peripheral Event System. Refer to Section
31. ”Peripheral Event Controller (PEVC)” on page 839 for details.
16.5 Functional Description
16.5.1
Basic Operation
The PDCA consists of multiple independent PDCA channels, each capable of handling DMA
requests in parallel. Each PDCA channels contains a set of configuration registers which must
be configured to start a DMA transfer.
In this section the steps necessary to configure one PDCA channel is outlined.
The peripheral to transfer data to or from must be configured correctly in the Peripheral Select
Register (PSR). This is performed by writing the Peripheral Identity (PID) value for the corre-
sponding peripheral to the PID field in the PSR register. The PID also encodes the transfer
direction, i.e. memory to peripheral or peripheral to memory. See Section 16.5.6.
The transfer size must be written to the Transfer Size field in the Mode Register (MR.SIZE). The
size must match the data size produced or consumed by the selected peripheral. See Section
16.5.7.
The memory address to transfer to or from, depending on the PSR, must be written to the Mem-
ory Address Register (MAR). For each transfer the memory address is increased by either a
one, two or four, depending on the size set in MR. See Section 16.5.2.
The number of data items to transfer is written to the TCR register. If the PDCA channel is
enabled, a transfer will start immediately after writing a non-zero value to TCR or the reload ver-
sion of TCR, TCRR. After each transfer the TCR value is decreased by one. Both MAR and TCR
can be read while the PDCA channel is active to monitor the DMA progress. See Section 16.5.3.
The channel must be enabled for a transfer to start. A channel is enable by writing a one to the
EN bit in the Control Register (CR).
16.5.2
Memory Pointer
Each channel has a 32-bit Memory Address Register (MAR). This register holds the memory
address for the next transfer to be performed. The register is automatically updated after each
transfer. The address will be increased by either one, two or four depending on the size of the
DMA transfer (byte, halfword or word). The MAR can be read at any time during transfer.
16.5.3
Transfer Counter
Each channel has a 16-bit Transfer Counter Register (TCR). This register must be written with
the number of transfers to be performed. The TCR register should contain the number of data
items to be transferred independently of the transfer size. The TCR can be read at any time dur-
ing transfer to see the number of remaining transfers.
16.5.4
Reload Registers
Both the MAR and the TCR have a reload register, respectively Memory Address Reload Regis-
ter (MARR) and Transfer Counter Reload Register (TCRR). These registers provide the
possibility for the PDCA to work on two memory buffers for each channel. When one buffer has
completed, MAR and TCR will be reloaded with the values in MARR and TCRR. The reload logic
is always enabled and will trigger if the TCR reaches zero while TCRR holds a non-zero value.
After reload, the MARR and TCRR registers are cleared.
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