Reading The Transfer Descriptors Of Active Channels - NXP Semiconductors freescale KV4 Series Reference Manual

to test the TCDn_CSR[START] bit and the TCDn_CSR[ACTIVE] bit. The minor-loop-
complete condition is indicated by both bits reading zero after the TCDn_CSR[START]
was set. Polling the TCDn_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:
Stage
START
1 1
2 0
3a 0
3b 0
The best method to test for minor-loop completion when using hardware, that is,
peripheral, initiated service requests is to read the TCDn_CITER field and test for a
change. The hardware request and acknowledge handshake signals are not visible in the
programmer's model.
The TCD status bits execute the following sequence for a hardware-activated channel:
Stage
START
1 0
2 0
3a 0
3b 0
For both activation types, the major-loop-complete status is explicitly indicated via the
TCDn_CSR[DONE] bit.
The TCDn_CSR[START] bit is cleared automatically when the channel begins execution
regardless of how the channel activates.

23.5.5.2 Reading the transfer descriptors of active channels

The eDMA reads back the true TCDn_SADDR, TCDn_DADDR, and TCDn_NBYTES
values if read while a channel executes. The true values of the SADDR, DADDR, and
NBYTES are the values the eDMA engine currently uses in its internal register file and
not the values in the TCD local memory for that channel. The addresses, SADDR and
Freescale Semiconductor, Inc.
TCDn_CSR bits
ACTIVE DONE
0 0
1 0
0 0
0 1
TCDn_CSR bits
ACTIVE DONE
0 0
1 0
0 0
0 1
KV4x Reference Manual, Rev. 2, 02/2015
Preliminary
Chapter 23 Direct Memory Access Controller (eDMA)
State
Channel service request via software
Channel is executing
Channel has completed the minor loop and is idle
Channel has completed the major loop and is idle
State
Channel service request via hardware (peripheral
request asserted)
Channel is executing
Channel has completed the minor loop and is idle
Channel has completed the major loop and is idle
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