Overview Of Dma Transfer - Fujitsu MB91260B Series Hardware Manual

CHAPTER 16 DMAC (DMA Controller)
16.6

Overview of DMA Transfer

This section explains the overview of the DMA transfer.
■ Block Size
• The value set in the block size setting register specifies the volume of data for each transfer operation
(× data width).
• The size of the data transferred in each transfer cycle is fixed the value specified by data width, and each
transfer consists of the number of transfer cycles specified by the block size.
• During a transfer, if a transfer request for a channel with a higher priority is received or if a transfer
pause request is issued, block transfer does not halt unless set to the boundary of a transfer unit.
Although this prevents undesirable splitting or pausing within a data block, it causes the response to be
slower if the block size is large.
• In the case of a reset, transfer halts immediately and therefore the validity of the transferred data cannot
be guaranteed.
■ Reload Operation
The following three reload functions can be configured for each channel in this module.
●
Transfer count register reload function
When the specified number of transfers completes, the transfer count register is reset with its initial value
and the DMAC waits for the next trigger.
Use this setting to perform any of the transfer sequences repeatedly.
If reloading is not enabled, the count register remains at zero after the specified number of transfers
complete and no further transfers are performed.
●
Reload function for transfer source address register
The transfer source address register is reset with its initial value after the specified number of transfers
complete.
Use this setting if repeatedly performing a transfer from a fixed region in the transfer source address range.
If reloading is not enabled, the value of the next transfer address remains set in the transfer source address
register after the specified number of transfers complete. Use this setting if the address range is not fixed.
●
Reload function for transfer destination address register
The transfer destination address register is reset with its initial value after the specified number of transfers
complete.
Use this setting if repeatedly performing a transfer to a fixed region in the transfer destination address
range.
Only enabling the reload functions for transfer source and destination registers does not restart after the
specified number of transfers complete. It only causes the address registers to be reset.
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