SH7021 datasheet(205/509 Pages) RENESAS

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1. Transfer requests are generated simultaneously to channels 1 and 0.

2. Channel 0 has a higher priority, so the channel 0 transfer begins first (channel 1 waits for

transfer).

3. A channel 3 transfer request occurs during the channel 0 transfer (channels 1 and 3 are both

waiting)

4. When the channel 0 transfer ends, channel 0 becomes lowest priority.

5. At this point, channel 3 has a higher priority than channel 1, so the channel 3 transfer begins

(channel 1 waits for transfer).

6. When the channel 3 transfer ends, channel 3 becomes lowest priority.

7. The channel 1 transfer begins.

8. When the channel 1 transfer ends, channels 1 and 2 shift downward in priority so that channel

1 becomes the lowest priority.

1, 3

None

(1) Channels 0 and 1

(3) Channel 3

(2) Channel 0

transfer starts

Priority order

changes

> 3 > 2 > 1

> 2 > 1 > 0

> 1 > 0 > 3

> 3 > 2 > 1

Transfer request

Waiting channel(s)

DMAC operation

Channel priority

(4) Channel 0

transfer ends

Priority order

changes

Priority order

changes

(5) Channel 3

transfer starts

(6) Channel 3

transfer ends

(7) Channel 1

transfer starts

(8) Channel 1

transfer ends

Figure 9.4 Changes in Channel Priority in Round-Robin Mode

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