SH7721 datasheet(493/1524 Pages) RENESAS

493 / 1524 page

Section 10

Direct Memory Access Controller (DMAC)

Rev. 3.00 Jan. 18, 2008 Page 431 of 1458

REJ09B0033-0300

10.4.3

Channel Priority

When the DMAC receives simultaneous transfer requests on two or more channels, it transfers

data according to a predetermined priority. Two modes (fixed mode and round-robin mode) are

selected by the PR1 and PR0 bits in DMAOR.

(1)

Fixed Mode

In this mode, the priority levels among the channels remain fixed. There are two kinds of fixed

modes as follows:

• CH0 > CH1 > CH2 > CH3 > CH4 > CH5

• CH0 > CH2 > CH3 > CH1 > CH4 > CH5

These are selected by the PR1 and the PR0 bits in DMAOR.

(2)

Round-Robin Mode

In round-robin mode each time data of one transfer unit (word, byte, longword, or 16-byte unit) is

transferred on one channel, the priority is rotated. The channel on which the transfer was just

finished rotates to the bottom of the priority. The round-robin mode operation is shown in figure

10.3. The priority of round-robin mode is CH0 > CH1 > CH2 > CH3 > CH4 > CH5 immediately

after a reset. When round-robin mode is specified, the same bus mode, either cycle steal mode or

burst mode, must be specified for all of the channels.

SH7721 Datasheet(PDF) 493 Page - Renesas Technology Corp