Atmel SAM9X25, Manual

Page: 481 / 1145

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11054A–ATARM–27-Jul-11
SAM9X25
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11054A–ATARM–27-Jul-11
SAM9X25
31.4.5 Programming a Channel
F our re gisters, the DMAC_DSCRx, the DM AC_CTRL Ax, th e DMAC_ CTRLBx an d
DMAC_CFGx, need to be programmed to set up whether single or multi-buffer transfers take
place, and which type of multi-buffer transfer is used. The different transfer types are shown in
Table 31-3 on page 479 .
The “BTSIZE, SADDR and DADDR” columns indicate where the values of DMAC_SARx,
DMAC_DARx, DMAC_CTLx, and DMAC_LLPx are obtained for the next buffer transfer when
multi-buffer DMAC transfers are enabled.
31.4.5.1 Programming Examples
Single-buffer Transfer (Row 1)
1. Read the Channel Handler Status Register DMAC_CHSR.ENABLE Field to choose a
free (disabled) channel.
2. Clear any pending interrupts on the channel from the previous DMAC transfer by read-
ing the interrupt status register, DMAC_EBCISR.
3. Program the following channel registers:
a. Write the starting source address in the DMAC_SADDRx register for channel x.
b. Write the starting destination address in the DMAC_DADDRx register for
channel x.
c. Write the next descriptor address in the DMA_DSCRx register for channel x with
0x0.
d. Program DMAC_CTRLAx, DMAC_CTRLBx and DMAC_CFGx according to Row 1
as shown in
Table 31-3 on page 479 . Program the DMAC_CTRLBx register with
both AUTO fields set to 0.
e. Write the control information for the DMAC transfer in the DMAC_CTRLAx and
DMAC_CTRLBx registers for channel x. For example, in the register, you can pro-
gram the following:
– i. Set up the transfer type (memory or non-memory peripheral for source and
destination) and flow control device by programming the FC of the DMAC_CTRLBx
register.
– ii. Set up the transfer characteristics, such as:
– Transfer width for the source in the SRC_WIDTH field.
– Transfer width for the destination in the DST_WIDTH field.
– Source AHB Master interface layer in the SIF field where source resides.
– Destination AHB Master Interface layer in the DIF field where destination resides.
– Incrementing/decrementing or fixed address for source in SRC_INC field.
– Incrementing/decrementing or fixed address for destination in DST_INC field.
f. Write the channel configuration information into the DMAC_CFGx register for chan-
nel x.
– i. Designate the handshaking interface type (hardware or software) for the source
and destination peripherals. This is not required for memory. This step requires
programming the SRC_H2SEL/DST_H2SEL bits, respectively. Writing a ‘1’ activates
the hardware handshaking interface to handle source/destination requests. Writing a
‘0’ activates the software handshaking interface to handle source/destination
requests.