DMA_DCRn field descriptions (continued)
Field
Description
10
DMA Channel 2
11
DMA Channel 3
LCH2
Link Channel 2
Indicates the DMA channel assigned as link channel 2. The link channel number cannot be the same as
the currently executing channel, and generates a configuration error if this is attempted (DSRn[CE] is set).
00
DMA Channel 0
01
DMA Channel 1
10
DMA Channel 2
11
DMA Channel 3
21.4 Functional Description
In the following discussion, the term DMA request implies that DCRn[START] is set, or
DCRn[ERQ] is set and then followed by assertion of the properly selected DMA
peripheral request. DCRn[START] is cleared when the channel is activated.
Before initiating a dual-address access, the DMA module verifies that DCRn[SSIZE] and
DCRn[DSIZE] are consistent with the source and destination addresses. If they are not
consistent, the configuration error bit, DSRn[CE], is set. If misalignment is detected, no
transfer occurs, DSRn[CE] is set, and, depending on the DCR configuration, an interrupt
event may be issued. If the auto-align bit, DCRn[AA], is set, error checking is performed
on the appropriate registers.
A read/write transfer sequence reads data from the source address and writes it to the
destination address. The number of bytes transferred is the largest of the sizes specified
by DCRn[SSIZE] and DCRn[DSIZE] in the DMA Control Registers (DCRn).
Source and destination address registers (SARn and DARn) can be programmed in the
DCRn to increment at the completion of a successful transfer.
21.4.1 Transfer requests (Cycle-Steal and Continuous modes)
The DMA channel supports software-initiated or peripheral-initiated requests. A request
is issued by setting DCRn[START] or when the selected peripheral request asserts and
DCRn[ERQ] is set. Setting DCRn[ERQ] enables recognition of the peripheral DMA
requests. Selecting between cycle-steal and continuous modes minimizes bus usage for
either type of request.
Chapter 21 DMA Controller Module
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
Freescale Semiconductor, Inc.
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Содержание MKL27Z128VFM4
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