Renesas SH7781 - Manual (Page 736)

14. Direct Memory Access Controller (DMAC)
Rev.1.00 Jan. 10, 2008 Page 706 of 1658
REJ09B0261-0100
14.4.2 Channel Priority
When the DMAC receives transfer requests on two or more channels simultaneously, it transfers
data according to a determined priority. Modes are chosen from among fixed mode and round-
robin mode. Modes are selected by bits PR1 and PR0 in DMAOR0 (channels 0 to 5) and
DMAOR1 (channels 6 to 11).
The relationship between channels 0 to 5 and channels 6 to 11 is round-robin.
The priority immediately after reset is CH0 to CH5 > CH6 to CH11.
(1) Fixed Mode
In fixed mode, the channel priority does not change. There are two kinds of fixed modes as
follows.
• Channels 0 to 5
⎯ CH0 > CH1 > CH2 > CH3 > CH4 > CH5
⎯ CH0 > CH2 > CH3 > CH1 > CH4 > CH5
• Channels 6 to 11
⎯ CH6 > CH7 > CH8 > CH9 > CH10 > CH11
⎯ CH6 > CH8 > CH9 > CH7 > CH10 > CH11
These are selected by bits PR1 and PR0 in DMAOR0 and DMAOR1.
(2)
Round-Robin Mode
In round-robin mode, each time data of one transfer unit (byte, word, longword, 16-byte, or 32-
byte unit) is transferred on one channel, the channel on which the transfer has just ended is the
bottom of the priority. Figure 14.2 shows the round-robin mode operation. The priority of round-
robin mode immediately after reset is CH0 > CH1 > CH2 > CH3 > CH4 > CH5, and CH6 > CH7
> CH8 > CH9 > CH10 > CH11.
When round-robin mode is specified, do not mix cycle steal mode and burst mode in all channels
(channels 0 to 5) corresponding to DMAOR0.
All channels (channels 6 to 11) corresponding to DMAOR1 can be set in only normal mode 2
(CHCR.LCKN=1, CHCR.TB=0) for cycle steal mode.