Motorola ColdFire MCF5281 - Manual (Page 309)

DMA Controller Module
Freescale Semiconductor 16-13
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] 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.
As soon as the channel has been initialized, it is started by writing a one to DCRn[START] or asserting
DREQn, depending on the status of DCRn[EEXT]. Programming the channel for internal requests causes
the channel to request the bus and start transferring data immediately. If the channel is programmed for
external request, DREQn must be asserted before the channel requests the bus.
Changes to DCRn are effective immediately while the channel is active. To avoid problems with changing
a DMA channel setup, write a one to DSRn[DONE] to stop the DMA channel.
16.5.4 Data Transfer
This section describes auto-alignment and bandwidth control for DMA transfers.
16.5.4.1 Auto-Alignment
Auto-alignment allows block transfers to occur at the optimal size based on the address, byte count, and
programmed size. To use this feature, DCRn[AA] must be set. The source is auto-aligned if DCRn[SSIZE]
indicates a transfer size larger than DCRn[DSIZE]. Source alignment takes precedence over the
destination when the source and destination sizes are equal. Otherwise, the destination is auto-aligned. The
address register chosen for alignment increments regardless of the increment value. Configuration error
checking is performed on registers not chosen for alignment.
If BCRn is greater than 16, the address determines transfer size. Bytes, words, or longwords are transferred
until the address is aligned to the programmed size boundary, at which time accesses begin using the
programmed size.
If BCRn is less than 16 at the start of a transfer, the number of bytes remaining dictates transfer size. For
example, AA = 1, SARn = 0x0001, BCRn = 0x00F0, SSIZE = 00 (longword), and DSIZE = 01 (byte).
Because SSIZE > DSIZE, the source is auto-aligned. Error checking is performed on destination registers.
The access sequence is as follows:
1. Read byte from 0x0001—write 1 byte, increment SARn.
2. Read word from 0x0002—write 2 bytes, increment SARn.
3. Read longword from 0x0004—write 4 bytes, increment SARn.
4. Repeat longwords until SARn = 0x00F0.
5. Read byte from 0x00F0—write byte, increment SARn.
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3