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Enhanced Direct Memory Access (eDMA)
Freescale Semiconductor
19-35
(0x1234567
x
) retain their original value. In this example the source address is set to 0x12345670, the
offset is set to 4 bytes and the MOD field is set to 4, allowing for a 2
4
byte (16-byte) size queue.
19.6.5
eDMA TCD
n
Status Monitoring
19.6.5.1
Minor Loop Complete
There are two methods to test for minor loop completion when using software initiated service requests.
The first is to read the TCD
n
_CITER field and test for a change. (Another method may be extracted from
the sequence shown below). The second method is to test the TCD
n
_CSR[START] bit and the
TCD
n
_CSR[ACTIVE] bit. The minor-loop-complete condition is indicated by both bits reading zero after
the TCD
n
_CSR[START] was set. Polling the TCD
n
_CSR[ACTIVE] bit may be inconclusive, because the
active status may be missed if the channel execution is short in duration.
The TCD status bits execute the following sequence for a software activated channel:
The best method to test for minor-loop completion when using hardware (peripheral) initiated service
requests is to read the TCD
n
_CITER field and test for a change. The hardware request and acknowledge
handshakes signals are not visible in the programmer’s model.
The TCD status bits execute the following sequence for a hardware-activated channel:
Table 19-34. Modulo Feature Example
Transfer
Number
Address
1
0x12345670
2
0x12345674
3
0x12345678
4
0x1234567C
5
0x12345670
6
0x12345674
TCD
n
_CSR bits
State
START
ACTIVE
DONE
1
1
0
0
Channel service request via software
2
0
1
0
Channel is executing
3a
0
0
0
Channel has completed the minor loop and is idle
3b
0
0
1
Channel has completed the major loop and is idle
Содержание MCF54455
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