RX610 Group
12. DMA Controller (DMAC)
R01UH0032EJ0120 Rev.1.20
Page 323 of 1006
Feb 20, 2013
12.3
Operation
12.3.1
Bus Mastership Release Timing
The DMAC must release bus mastership for an interval of at least one cycle per single operation of data reading and
writing. The bus is thus accessible by another master (CPU or DTC) during this interval.
Furthermore, access by the CPU (except with the DMAC as the target) is possible during access by the DMAC.
However, when the external bus is set as the source or destination for transfer by the DMAC, access over the internal bus
by the CPU and DTC may become impossible due to the relation between the clock and the timing of access. In such
cases, divided up the data for transfer by the DMAC into smaller units and handle transfer in these units so that the CPU
and DTC become able to accept access requests when transfer-completed interrupts are conveyed to the CPU and DTC.
For details, refer to section 11, Bus.
Figure 12.2 shows an example of how bus mastership passes between the DMAC and other bus masters.
(1) The CPU with bus mastership can access areas other than the DMAC read and
write targets.
System clock
Read
Read
Read
Read
Write
Write
Write
Write
CPU/DTC
Single-operand transfer
Single-operand transfer
DMAC source
DMAC destination
: Master that has bus mastership
(1)
(1)
(1)
(1)
(1)
(1)
Figure 12.2 Example of how Bus Mastership Passes between the DMAC and Other Bus Masters