SH7243 datasheet(445/1726 Pages) RENESAS

445 / 1726 page

Section 10 Direct Memory Access Controller (DMAC)

Rev. 1.00 Jun. 26, 2008 Page 415 of 1692

REJ09B0393-0100

10.4.3

Channel Priority

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

channel according to a predetermined priority order. Three modes (fixed mode 1, fixed mode 2,

and round-robin mode) are selected using the PR1 and PR0 bits in DMAOR.

(1)

Fixed Mode

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

modes as follows:

Fixed mode 1: CH0 > CH1 > CH2 > CH3 > CH4 > CH5 > CH6 > CH7

Fixed mode 2: CH0 > CH4 > CH1 > CH5 > CH2 > CH6 > CH3 > CH7

These are selected by the PR1 and PR0 bits in the DMA operation register (DMAOR).

(2)

Round-Robin Mode

Each time one unit of word, byte, longword, or 16 bytes is transferred on one channel, the priority

order is rotated. The channel on which the transfer was just finished is rotated to the lowest of the

priority order among the four round-robin channels (channels 0 to 4). The priority of the channels

other than the round-robin channels (channels 0 to 4) does not change even in round-robin mode.

The round-robin mode operation is shown in figure 10.3. The priority in round-robin mode is CH0

> CH1 > CH2 > CH3 > CH4 > CH5 > CH6 > CH7 immediately after a reset.

When round-robin mode has been specified, do not concurrently specify cycle steal mode and

burst mode as the bus modes of any two or more channels.

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