HD6417705 Datasheet, PDF (304/739 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

Round-Robin Mode: Each time one byte, word, longword, or 16-byte 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 8.3. The
priority of round-robin mode is CH0 > CH1 > CH2 > CH3 immediately after a reset.
When the round-robin mode is specified, cycle-steal mode and burst mode should not be mixed
among the bus modes for multiple channels.
(1) When channel 0 transfers
Initial priority order
CH0 > CH1 > CH2 > CH3
Priority order
after transfer
CH 1 > CH2 > CH3 > CH0
Channel 0 becomes bottom
priority
(2) When channel 1 transfers
Initial priority order
CH0 > CH1 > CH2 > CH3
Priority order
after transfer
CH2 > CH3 > CH0 > CH1
Channel 1 becomes bottom
priority.
The priority of channel 0, which
was higher than channel 1, is also
shifted.
(3) When channel 2 transfers
Initial priority order
CH0 > CH1 > CH2 > CH3
Priority order
after transfer
CH3 > CH0 > CH1 > CH2
Post-transfer priority order
when there is an
immediate transfer
request to channel 1 only
CH2 > CH3 > CH0 > CH1
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 3 and 0, which were
higher than channel 1, are also
shifted.
(4) When channel 3 transfers
Initial priority order
CH0 > CH1 > CH2 > CH3
Priority order
after transfer
CH0 > CH1 > CH2 > CH3
Priority order does not change
Figure 8.3 Round-Robin Mode
Rev. 2.00, 09/03, page 258 of 690