Silicon Laboratories EFR32xG14 Wireless Gecko Reference Manual page 166

8.3.7.2 SYNC Descriptor Structure
This descriptor defines an intra-channel synchronizing structure. It allows the channel to wait for some external stimulus before continu-
ing on to the next descriptor. This structure is also used to provide stimulus to another channel to indicate that it may continue.
For example channel 1 may be configured to transfer a header into a buffer while channel 2 is simultaneously transferring data into the
same structure. When channel 1 has completed it can wait for a sync signal from channel 2 before transferring the now complete buffer
to a peripheral.
Synch descriptors do nothing until a condition is met. The condition is formed by the SYNCTRIG field in the LDMA_SYNC register and
the MATCHEN and MATCHVAL fields of the descriptor. When (SYNCTRIG & MATCHEN) == (MATCHVAL & MATCHEN) the next de-
scriptor is loaded. In addition to waiting for the condition a Link descriptor can set or clear bits in SYNCTRIG to meet the conditions of
another channel and cause it to continue. The CPU also has the ability to set and clear the SYNCTRIG bits from software.
This structure type can only be linked in from memory.
For specifying SYNC structure type, set STRUCTTYPE to 1.
Bit Name
1:0 STRUCTTYPE
This field indicates which type of descriptor this is. It must be 1 for a SYNC descriptor.
20 DONEIFSEN
If set the interrupt flag will be set when descriptor completes.
15:8 SYNCCLR
This bit-field is used to clear corresponding bits within the SYNCTRIG field of the SYNC LDMA_SYNC register. To clear
a given bit, a one should be loaded to the corresponding bit. Set is given priority over clear if both corresponding bits
are loaded with a one. The sync trigger clear function can only be used when loaded from a linked structure. Alternate-
ly, the user can directly write the SYNCTRIG bit-field if required.
7:0 SYNCSET
This bit-field is used to set corresponding bits within the SYNCTRIG bit-field. To set a given bit, a one should be loaded
to the corresponding bit. Set is given priority over clear if both corresponding bits are loaded with a one. The sync trig-
ger set function can only be used when loaded from a linked structure. Alternately, the user can directly write the SYN-
CTRIG bit-field if required.
15:8 MATCHEN
This bit-field serves as the SYNCTRIG match enable. A sync match triggers the load of the next linked DMA structure
as specified by link_mode, when: (SYNCTRIG & MATCHEN) == (MATCHVAL & MATCHEN).
7:0 MATCHVAL
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Bit Position
LINKADDR
Description
Descriptor Type
Done if Set indicator
Sync Trigger Clear
Sync Trigger Set
Sync Trigger Match Enable
Sync Trigger Match Value
LDMA - Linked DMA Controller
SYNCCLR
MATCHEN
Reference Manual
SYNCSET
MATCHVAL
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