K60P100M100SF2RM Datasheet, PDF (502/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Initialization/application information
DADDR, and NBYTES, decrements to zero as the transfer progresses, can give an
indication of the progress of the transfer. All other values are read back from the TCD
local memory.
21.5.5.3 Checking channel preemption status
Preemption is available only when fixed arbitration is selected as the channel arbitration
mode. A preemptive situation is one in which a preempt-enabled channel runs and a
higher priority request becomes active. When the eDMA engine is not operating in fixed
channel arbitration mode, the determination of the actively running relative priority
outstanding requests become undefined. Channel priorities are treated as equal, that is,
constantly rotating, when Round-Robin Arbitration mode is selected.
The TCDn_CSR[ACTIVE] bit for the preempted channel remains asserted throughout
the preemption. The preempted channel is temporarily suspended while the preempting
channel executes one major loop iteration. If two TCDn_CSR[ACTIVE] bits are set
simultaneously in the global TCD map, a higher priority channel is actively preempting a
lower priority channel.
21.5.6 Dynamic programming
21.5.6.1 Dynamically changing the channel priority
The following two options are recommended for dynamically changing channel priority
levels:
1. Switch to Round-Robin Channel Arbitration mode, change the channel priorities,
then switch back to Fixed Arbitration mode,
2. Disable all the channels, change the channel priorities, then enable the appropriate
channels.
21.5.6.2 Dynamically changing the channel linking and scatter/gather
options
Dynamic channel linking and dynamic scatter/gather is the process of changing the
TCDn_CSR[MAJOR_E_LINK] or TCDn_CSR[E_SG] bits during channel execution.
These bits are read from the TCD local memory at the end of channel execution,
therefore allowing software to enable either feature during channel execution.
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
502
Freescale Semiconductor, Inc.