CHAPTER 11: DSTC
518 FM4 Peripheral Manual, Doc. No. 002-04856 Rev. *E
Operations of Chain Start
Using the Chain Start enables making a Start Trigger for different transfers set in multiple DES.
Figure 3-3 illustrates how the DES reference and transfer operation are executed when the DSTC
executes a Chain Start on the next DES. 1st-DES is located at the position of DESP0. The size of
1st-DES is defined by the value of ORL[2:0] of 1st-DES. If there is a Chain Start Trigger in the DES after
1st-DES, the DSTC computes DESP1 of the succeeding 2nd-DES from the DESP0 and the size of
1st-DES. The DSTC starts a transfer specified in 2nd-DES after referring to details of 2nd-DES.
Therefore, the succeeding 2nd-DES to be started by the Chain Start must be located next to 1st-DES
started first.
Specifying the Chain Start in 2nd-DES can start the transfer of 3rd-DES. The DSTC can keep executing
the Chain Start transfer until there is no more Chain Start Trigger within the maximum number of DES
that can be built.
Figure 3-3 DES Reference in Chain Start Transfer
DES2 (SA0)
DES3 (DA0)
DES0 (Control0)
DES1 (Count0)
1st-DES
2nd-DES
3rd-DES
DES2 (SA1)
DES3 (DA1)
DES0 (Control1)
DES1 (Count1)
DES2 (SA2)
DES3 (DA2)
DES0 (Control2)
DES1 (Count2)
data
data
data
data
data
data2
Chain Start Trigger
Transfer
operation
(1st-DES)
Transfer
operation
(2nd-DES)
Transfer
operation
(3rd-DES)
DESP0
DESP0 +
1st-DES size
DESP1
DESP2
DESP1 +
2nd-DES size
Chain Start Trigger
SA0
DA0
SA1
DA1
SA2
DA2
Transfer memory areaDES memory area
DES4 (Count1 OuterReload)
DES4 (Count1 OuterReload)
DES6 (DA2 OuterReload)
Chain Lock Function
The DSTC may execute other transfer first according to the transfer priority order if there is a transfer start
request of other source at the timing of a Chain Start. If that occurs, the DSTC executes a specified Chain
start transfer after executing other transfer. The Chain Lock Function ensures that in the situation
described above, transfers started by a Chain Start are executed successively and that no other transfer
request interrupts the transfers, regardless of the transfer priority order. The Chain Lock Function can be
enabled by writing 1 to CHLK in a DES.
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