General Aspects Of Dma Transfer - Fujitsu FR60 Hardware Manual

CHAPTER 14 DMA CONTROLLER (DMAC)

14.3.3 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 x 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 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 decreases.
• 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.)
• If only reloading of the transfer source/transfer destination register is enabled, restart after
transfer is performed the specified number of times is not implemented and only the values
of each address register are set.
414