HD6417021 Hitachi Semiconductor, HD6417021 Datasheet - Page 202

• Manufacturer Part Number: HD6417021
• Description: SuperH RISC engine
• Manufacturer: Hitachi Semiconductor

Figure 9.4 shows how the priority order changes when channel 0 and channel 1 transfers are
requested simultaneously and a channel 3 transfer is requested during the channel 0 transfer. The
DMAC operates as follows:
(1) When channel 0 transfers
Initial priority order
Priority order
after transfer
(2) When channel 3 transfers
Initial priority order
Priority order
after transfer
(3) When channel 2 transfers
Initial priority order
Priority order
after transfer
Post-transfer priority order when
there is an immediate transfer
request to channel 3 only
(4) When channel 1 transfers
Initial priority order
Priority order
after transfer
ch0
ch0
ch0
ch0
ch0
ch1
ch3
ch3
ch3
ch3
ch3
ch3
ch2
Figure 9.3 Round-Robin Mode
ch0
ch2
ch2
ch2
ch2
ch2
ch2
ch1
ch2
ch3
ch1
ch1
ch1
ch1
ch1
ch1
ch0
ch1
ch2
ch0
ch3
ch0
ch3
Channel 0 becomes
bottom priority
Channel 3 becomes bottom
priority. The priority of channel
0, which was higher than
channel 3, is also shifted.
Channel 2 becomes bottom
priority. The priority of channels
0and 3, which were higher than
channel 2, are also shifted.
If immediately thereafter there
is a request to transfer channel
3 only, channel 3 becomes
bottom priority and the priority
of channels 0 and 1, which
were higher than channel 3,
are also shifted.
Priority order does not change
HITACHI 187