Renesas SH7641 - Manual (Page 480)

Section 13 Direct Memory Access Controller (DMAC)
Rev. 4.00 Sep. 14, 2005 Page 430 of 982
REJ09B0023-0400
These are selected by the PR1 and the PR0 bits in the DMA operation register (DMAOR).
Round-Robin Mode: Each time one word, byte, or longword is transferred on one channel, the
priority order is rotated. The channel on which the transfer was just finished rotates to the bottom
of the priority order. The round-robin mode operation is shown in figure 13.3. The priority of the
round-robin mode is CH0 > CH1 > CH2 > CH3 immediately after reset.
When the round-robin mode has been specified, do not concurrently specify cycle steal mode and
burst mode as the bus modes of any two channels.
CH1 > CH2 > CH3 > CH0
CH0 > CH1 > CH2 > CH3
CH2 > CH3 > CH0 > CH1
CH0 > CH1 > CH2 > CH3
CH2 > CH3 > CH0 > CH1
CH0 > CH1 > CH2 > CH3
CH0 > CH1 > CH2 > CH3
CH3 > CH0 > CH1 > CH2
CH0 > CH1 > CH2 > CH3
(1) When channel 0 transfers
Initial priority order
Initial priority order
Initial priority order
Priority order
afrer transfer
Priority order
afrer transfer
Priority order does not change
Channel 2 becomes bottom
priority.
The priority of channels 0 and 1,
which were higher than channel 2,
are also shifted. If immediately
after there is a request to transfer
channel 1 only, channel 1 becomes
bottom priority and the priority of
channels 0 and 3, which were
higher than channel 1, are also
shifted.
Channel 1 becomes bottom
priority.
The priority of channel 0, which
was higher than channel 1, is also
shifted.
Channel 0 becomes bottom
priority
Priority order
afrer transfer
Priority order
afrer transfer
Priority order
afrer transfer
Post-transfer priority order
when there is an
immediate transfer
request to channel 5 only
(2) When channel 1 transfers
(3) When channel 2 transfers
(4) When channel 3 transfers
Figure 13.3 Round-Robin Mode