Freescale Semiconductor ColdFire MCF52210 - Manual (Page 287)

DMA Controller Module
MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor 17-13
17.4.3 Channel Initialization and Startup
Before a block transfer starts, channel registers must be initialized with information describing
configuration, request-generation method, and the data block.
17.4.3.1 Channel Prioritization
The four DMA channels are prioritized in ascending order (channel 0 having highest priority and channel
3 having the lowest) or in an order determined by DCRn[BWC]. If the BWC encoding for a DMA channel
is 000, that channel has priority only over the channel immediately preceding it. For example, if
DCR3[BWC] equals 000, DMA channel 3 has priority over DMA channel 2 (assuming DCR2[BWC]
≠
000), but not over DMA channel 1.
If DCR0[BWC] equals 000 and DCR1[BWC] equals 000, DMA0 continues having priority over DMA1.
In this case, DCR1[BWC] equals 000 does not affect prioritization.
Simultaneous external requests are prioritized in ascending order or in an order determined by each
channel’s DCRn[BWC] bits.
17.4.3.2 Programming the DMA Controller Module
General guidelines for programming the DMA are:
• No mechanism exists within the DMA module itself to prevent writes to control registers during
DMA accesses.
• If the DCRn[BWC] value of sequential channels are equal, the channels are prioritized in
ascending order.
The DMAREQC register is configured to assign peripheral DMA requests to the individual DMA
channels.
The SARn is loaded with the source (read) address. If the transfer is from a peripheral device to memory,
the source address is the location of the peripheral data register. If the transfer is from memory to a
peripheral device or memory, the source address is the starting address of the data block. This can be any
aligned byte address.
The DARn should contain the destination (write) address. If the transfer is from a peripheral device to
memory, or from memory to memory, the DARn is loaded with the starting address of the data block to be
written. If the transfer is from memory to a peripheral device, DARn is loaded with the address of the
peripheral data register. This address can be any aligned byte address.
SARn and DARn change after each cycle depending on DCRn[SSIZE,DSIZE,
SINC,DINC,SMOD,DMOD] and on the starting address. Increment values can be 1, 2, 4, or 16 for byte,
word, longword, or 16-byte line transfers, respectively. If the address register is programmed to remain
unchanged (no count), the register is not incremented after the data transfer.
BCRn[BCR] must be loaded with the number of byte transfers to occur. It is decremented by 1, 2, 4, or 16
at the end of each transfer, depending on the transfer size. DSRn[DONE] must be cleared for channel
startup.