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Enhanced Direct Memory Access Controller (eDMA)
MPC5644A Microcontroller Reference Manual, Rev. 6
164
Freescale Semiconductor
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. See
Channel pre-emption is enabled on a per-channel basis by setting the ECP bit in the EDMA_CPR
n
register.
Channel pre-emption allows the executing channel’s data transfers to be temporarily suspended in favor
of starting a higher priority channel. After the pre-empting channel has completed all its minor loop data
transfers, the pre-empted channel is restored and resumes execution. After the restored channel completes
one read/write sequence, it is again eligible for pre-emption. If any higher priority channel requests
service, the restored channel is suspended and the higher priority channel is serviced. Nested pre-emption
(attempting to pre-empt a pre-empting channel) is not supported. After a pre-empting channel begins
execution, it cannot be pre-empted. Pre-emption is available only when fixed arbitration is selected for
both group and channel arbitration modes.
A channel’s ability to pre-empt another channel can be disabled by setting EDMA_CPR[DPA]. When a
channel’s pre-empt ability is disabled, that channel cannot suspend a lower priority channel’s data transfer;
regardless of the lower priority channel’s ECP setting. This allows for a pool of low priority, large data
moving channels to be defined. These low priority channels can be configured to not pre-empt each other,
thus preventing a low priority channel from consuming the pre-empt slot normally available a true, high
priority channel.
Address: EDM
n
Access: User read/write
0
1
2
3
4
5
6
7
R
ECP
DPA
GRPPRI
CHPRI
W
Reset
0
0
0
0
1
The reset value for the channel priority field, CHPRI[0–3], is equal to the corresponding channel
number for each priority register; that is, EDMA_CPRI0[CHPRI] = 0b0000 and
EDMA_CPR15[CHPRI] = 0b1111.
Figure 8-22. eDMA Channel n Priority Register (EDMA_CPRn)
Table 8-18. EDMA_CPRn field descriptions
Field
Description
ECP
Enable Channel Pre-emption
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.
DPA
Disable pre-empt ability
0 Channel n can suspend a lower priority channel.
1 Channel n cannot suspend any channel, regardless of channel priority.
Содержание MPC5644A
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