Motorola DSP56301 - Manual (Page 106)

DMA Control Registers 5–0 (DCR[5–0])
4 -32 DSP56301 User’s Manual
18–17
cont.
DPR[1–0]
OMR - CDP[1–0] CP[1–0] Core Priority
00 00 0 (lowest)
00 01 1
00 10 2
00 11 3 (highest)
01 xx DMA accesses have higher priority than core
accesses
10 xx DMA accesses have the same priority as core
accesses
11 xx DMA accesses have lower priority than core
accesses
n
If DMA priority > core priority (for example, if CDP = 01, or CDP = 00 and
DPR > CP), the DMA performs the external bus access first and the core waits for the
DMA channel to complete the current transfer.
n
If DMA priority = core priority (for example, if CDP = 10, or CDP = 00 and
DPR = CP), the core performs all its external accesses first and then the DMA channel
performs its access.
n
If DMA priority < core priority (for example, if CDP=11, or CDP = 00 and
DPR < CP), the core performs its external accesses and the DMA waits for a free slot
in which the core does not require the external bus.
n
In Dynamic Priority mode (CDP = 00), the DMA channel can be halted before
executing both the source and destination accesses if the core has higher priority. If
another higher-priority DMA channel requests access, the halted channel finishes its
previous access with a new higher priority before the new requesting DMA channel is
serviced.
16 DCON 0 DMA Continuous Mode Enable
Enables/disables DMA Continuous mode. When DCON is set, the channel enters the
Continuous Transfer mode and cannot be interrupted during a transfer by any other DMA
channel of equal priority. DMA transfers in the continuous mode of operation can be
interrupted if a DMA channel of higher priority is enabled after the continuous mode transfer
starts. If the priority of the DMA transfer in continuous mode (that is, DCON = 1) is higher
than the core priority (CDP = 01, or CDP = 00 and DPR > CP), and if the DMA requires an
external access, the DMA gets the external bus and the core is not able to use the external
bus in the next cycle after the DMA access even if the DMA does not need the bus in this
cycle. However, if a refresh cycle from the DRAM controller is requested, the refresh cycle
interrupts the DMA transfer. When DCON is cleared, the priority algorithm operates as for the
DPR bits.
Table 4-12. DMA Control Register (DCR) Bit Definitions (Continued)
Bit
Number
Bit Name
Reset
Value
Description