SAM4L Datasheet, PDF (315/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
If TCR is zero when writing to TCRR, the TCR and MAR are automatically updated with the
value written in TCRR and MARR.
16.5.5
Ring Buffer
When Ring Buffer mode is enabled the TCRR and MARR registers will not be cleared when
TCR and MAR registers reload. This allows the PDCA to read or write to the same memory
region over and over again until the transfer is actively stopped by the user. Ring Buffer mode is
enabled by writing a one to the Ring Buffer bit in the Mode Register (MR.RING).
16.5.6
Peripheral Selection
The Peripheral Select Register (PSR) decides which peripheral should be connected to the
PDCA channel. A peripheral is selected by writing the corresponding Peripheral Identity (PID) to
the PID field in the PSR register. Writing the PID will both select the direction of the transfer
(memory to peripheral or peripheral to memory), which handshake interface to use, and the
address of the peripheral holding register. Refer to the Peripheral Identity (PID) table in the Mod-
ule Configuration section for the peripheral PID values.
16.5.7
Transfer Size
The transfer size can be set individually for each channel to be either byte, halfword or word (8-
bit, 16-bit or 32-bit respectively). Transfer size is set by writing the desired value to the Transfer
Size field in the Mode Register (MR.SIZE).
When the PDCA moves data between peripherals and memory, data is automatically sized and
aligned. When memory is accessed, the size specified in MR.SIZE and system alignment is
used. When a peripheral register is accessed the data to be transferred is converted to a word
where bit n in the data corresponds to bit n in the peripheral register. If the transfer size is byte or
halfword, bits greater than 8 and16 respectively are set to zero.
Refer to the Module Configuration section for information regarding what peripheral registers are
used for the different peripherals and then to the peripheral specific chapter for information
about the size option available for the different registers.
16.5.8
Enabling and Disabling
Each DMA channel is enabled by writing a one to the Transfer Enable bit in the Control Register
(CR.TEN) and disabled by writing a one to the Transfer Disable bit (CR.TDIS). The current sta-
tus can be read from the Status Register (SR).
While the PDCA channel is enabled all DMA request will be handled as long the TCR and TCRR
is not zero.
16.5.9 Interrupts
Interrupts can be enabled by writing a one to the corresponding bit in the Interrupt Enable Regis-
ter (IER) and disabled by writing a one to the corresponding bit in the Interrupt Disable Register
(IDR). The Interrupt Mask Register (IMR) can be read to see whether an interrupt is enabled or
not. The current status of an interrupt source can be read through the Interrupt Status Register
(ISR).
The PDCA has three interrupt sources:
• Reload Counter Zero - The TCRR register is zero.
• Transfer Finished - Both the TCR and TCRR registers are zero.
• Transfer Error - An error has occurred in accessing memory.
42023C–SAM–02/2013
315