Chapter 18 Enhanced Direct Memory Access (eDMA)
MPC5602P Microcontroller Reference Manual, Rev. 4
Freescale Semiconductor
399
18.5.2.16 eDMA Channel n Priority Registers (EDMA_CPRn)
When the fixed-priority channel arbitration mode is enabled (EDMA_CR[ERCA] = 0), the contents of
these registers define the unique priorities associated with each channel within a group. The channel
priorities are evaluated by numeric value; that is, 0 is the lowest priority, 1 is the next higher priority, then
2, 3, etc. If software chooses to modify channel priority values, then the software must ensure that the
channel priorities contain unique values, otherwise a configuration error is reported. The range of the
priority value is limited to the values of 0 through 15. When read, the GRPPRI bits of the EDMA_CPR
n
register reflect the current priority level of the group of channels in which the corresponding channel
resides. GRPPRI bits are not affected by writes to the EDMA_CPR
n
registers. The group priority is
assigned in the EDMA_CR.
Refer to
Channel preemption is enabled on a per-channel basis by setting the ECP bit in the EDMA_CPR
n
register.
Channel preemption allows the executing channel’s data transfers to be temporarily suspended in favor of
starting a higher priority channel. After the preempting channel has completed all of its minor loop data
transfers, the preempted channel is restored and resumes execution. After the restored channel completes
one read/write sequence, it is again eligible for preemption. If any higher priority channel is requesting
service, the restored channel is suspended and the higher priority channel is serviced. Nested preemption
(attempting to preempt a preempting channel) is not supported. After a preempting channel begins
execution, it cannot be preempted. Preemption is only available when fixed arbitration is selected for both
group and channel arbitration modes.
The following table describes the fields in the eDMA channel
n
priority register:
Address: Base + 0x100 +
n
Access: User read/write
0
1
2
3
4
5
6
7
R
ECP
0
0
0
CHPRI
W
Reset
0
0
0
0
—
1
1
The reset value for the channel priority fields, GRPPRI[0–1] and CHPRI[0–3] is the
channel number for the priority register;
EDMA_CPR15[CHPRI] = 0b1111.
Figure 18-17. eDMA Channel
n
Priority Register (EDMA_CPR
n
)
Table 18-17. EDMA_CPR
n
field descriptions
Field
Description
0
ECP
Enable channel preemption.
0 Channel
n
cannot be suspended by a higher priority channel’s service request.
1 Channel
n
can be temporarily suspended by the service request of a higher priority channel.
1-3
Reserved.
4–7
CHPRI[0:3]
Channel
n
arbitration priority. Channel priority when fixed-priority arbitration is enabled. The reset
value for the channel priority fields CHPRI[0–3], is equal to the corresponding channel number for
each priority register; that is, EDMA_CPR31[CHPRI] = 0b1111.
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