Datasheet

SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
926
37.8.6.2 Block Length is Not Multiple of 4 and Padding Not Used (ROPT field in HSMCI_DMA register set to 0)
In the previous DMA transfer flow (block length multiple of 4), the DMA controller is configured to use only WORD
AHB access. When the block length is no longer a multiple of 4 this is no longer true. The DMA controller is
programmed to copy exactly the block length number of bytes using 2 transfer descriptors.
1. Use the previous step until READ_SINGLE_BLOCK then
2. Program the DMA controller to use a two descriptors linked list.
a.Read the channel Register to choose an available (disabled) channel.
b.Clear any pending interrupts on the channel from the previous DMA transfer by reading the
DMAC_EBCISR register.
c. Program the channel registers in the Memory for the first descriptor. This descriptor will be word ori-
ented. This descriptor is referred to as LLI_W, standing for LLI word oriented transfe
r.
d
. The LLI_W.DMAC_SADDRx field in memory must be set with the starting address of the
HSMCI_FIFO address.
e. The LLI_W.DMAC_DADDRx field in the memory must be word aligned.
f. Program LLI_W.DMAC_CTRLAx with the following field’s values:
–DST_WIDTH is set to WORD.
–SRC_WIDTH is set to WORD.
–SCSIZE must be set according to the value of HSMCI_DMA, CHKSIZE field.
–BTSIZE is programmed with block_length/4. If BTSIZE is zero, this descriptor is skipped later.
g.
Pro
gram LLI_W.DMAC_CTRLBx with the following field’s values:
–DST_INCR is set to INCR
–SRC_INCR is set to INCR
–FC field is programmed with peripheral to memory flow control mode.
–SRC_DSCR is set to zero. (descriptor fetch is enabled for the SRC)
–DST_DSCR is set to one. (descriptor fetch is disabled for the DST)
–DIF and SIF are set with their respective layer ID. If SIF is different from DIF, DMA controller is able
to prefetch data and write HSMCI simultane
ously
.
h. Program LLI_W.DMAC_CFGx register for channel x with the following field’s values:
–FIFOCFG defines the watermark of the DMA channel FIFO.
–DST_REP is set to zero meaning that address are contiguous.
–SRC_H2SEL is set to true to enable hardware handshaking on the destination.
–SRC_PER is programmed with the hardware handshaking ID of the targeted HSMCI Host
Controller.
i. Program LLI
_W.DMAC_DSCR
x with the address of LLI_B descriptor. And s et DSCRx_IF to the AHB
Layer ID. This operation actually links the Word oriented descriptor on the second byte oriented
descriptor. When block_length[1:0] is equal to 0 (multiple of 4) LLI_W.DMAC_DSCRx points to 0, only
LLI_W is relevant.
j. Program the channel registers in the Memory for the second descriptor. This descriptor will be byte
oriented. This descriptor is referred to as LLI_B, standing for LLI Byte oriented.
k. The LLI_B.DMAC_SADDRx field in memory must be set with the starting address of
the
HSMC
I_FIFO a ddress.
l. The LLI_B.DMAC_DADDRx is not relevant if previous word aligned descriptor was enabled. If 1, 2 or
3 bytes are transferred that address is user defined and not word aligned.
m. Program LLI_B.DMAC_CTRLAx with the following field’s values:
–DST_WIDTH is set to BYTE.