C2510Fx / CC2511Fx
13.5.2 DMA Configuration Parameters
Variable Length Transfers: When VLEN≠000
and VLEN≠111, the DMA channel will use the
first byte or word (for word, bits 12:0 are used)
in source data as the transfer count, hence
allowing variable length transfers. When using
variable length transfer, various options
regarding how to count number of bytes to
transfer is given.
Setup and control of the DMA operation is
performed by the user software. This section
describes the parameters which must be
configured before a DMA channel can be
used. Section 13.5.3 on Page 103 describes
how the parameters are set up in software and
passed to the DMA controller.
Options are:
The behavior of each of the five DMA
channels is configured with the following
parameters:
1. Default: Transfer number of bytes/words
commanded by first byte/word + 1
(transfers length byte/word, and then as
many bytes/words as dictated by length
byte/word)
13.5.2.1 Source Address (SRCADDR)
The address of the location in XDATA memory
space where the DMA channel shall start to
read data for the transfer.
2. Transfer
number
of
bytes/words
commanded by first byte/word (transfers
length byte/word, and then as many
bytes/words as dictated by length
byte/word - 1)
13.5.2.2 Destination Address (DESTADDR)
3. Transfer
number
of
bytes/words
The address of the location in XDATA memory
space where the DMA channel will write the
data read from the source address. The user
must ensure that the destination is writable.
commanded by first byte/word + 2
(transfers length byte/word, and then as
many bytes/words as dictated by length
byte/word + 1)
4. Transfer
number
of
bytes/words
13.5.2.3 Transfer Count
commanded by first byte/word + 3
(transfers length byte/word, and then as
many bytes/words as dictated by length
byte/word + 2)
The number of bytes/words needed to be
transferred for the DMA transfer to be
complete. When the transfer count is reached,
the DMA controller rearms or disarms the
DMA channel (depending on transfer mode)
and alert the CPU by setting the
DMAIRQ.DMAIFn bit to 1. If IRQMASK=1,
IRCON.DMAIFwill also be set and an interrupt
request is generated if IEN1.DMAIE=1. The
transfer count can be of fixed or variable
length depending on how the DMA channel is
configured.
In any case, the LEN setting is used as
maximum transfer count. LEN should be set to
the largest allowed transfer count (specified by
the first byte or word) plus one.
Note that the M8 bit is only used when byte
size transfers are chosen.
Figure 26 shows the different VLENoptions.
Fixed Length Transfers: When VLEN=000or
VLEN=111, the length is set by the LENsetting
SWRS055D
Page 101 of 243
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