General Aspects Of Dma Transfer - Fujitsu MB91319 Series Hardware Manual

16.3.3

General Aspects of DMA Transfer

This section describes the block size for DMA transfers and the reload operation.
■ Block Size
• The unit and increment for transfer data is a set of (the number set in the block size
specification register × data width) data.
• Since the amount of data transferred in one transfer cycle is determined by the value specified
as the data width, one transfer unit is consists of the number of transfer cycles for the
specified block size.
• If a transfer request with a higher priority is received during transfer or if a temporary stop
request for a transfer occurs, the transfer stops only at the transfer unit boundary, whether or
not the transfer is a block transfer. This arrangement makes it possible to protect data for
which division or temporary stopping is not desirable. However, if the block size is large,
response time increases.
• Transfer stops immediately only when a reset occurs, in which case the data being transferred
cannot be guaranteed.
■ Reload Operation
In this module, the following three types of reloading can be set for each channel:
❍ Transfer count register reloading
After transfer is performed the specified number of times, the initial value is set in the transfer
count register again and waiting for a start request starts.
Set this type of reloading when the entire transfer sequence is to be performed repeatedly.
If reload is not specified, the count register value remains 0 after the transfer is performed the
specified number of times and no further transfer is performed.
❍ Transfer source address register reloading
After transfer is performed the specified number of times, the initial value is set in the transfer
source address register again.
Set this type of reloading when transfer is to be repeated from a fixed area in the transfer source
address area.
If reload is not specified, the transfer source address register value after the transfer is performed
the specified number of times becomes the next address. Use this type when the address area is
not fixed.
❍ Transfer destination address register reloading
After transfer is performed the specified number of times, the initial value is set in the transfer
destination address register again.
Set this type of reloading when transfer is to be repeated to a fixed area in the transfer destination
address area.
(The processing hereafter is the same as described in "Transfer source address register
reloading" above.)
CHAPTER 16 DMA CONTROLLER (DMAC)
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