CHAPTER 11: DSTC
520 FM4 Peripheral Manual, Doc. No. 002-04856 Rev. *E
If details of a transfer defined in a DES are fixed, and the CPU has to reuse details of the DES, setting DV
to"11" grants the ownership of the DES to the DSTC. In this situation, since the DES close process is not
executed after the transfer, the process of CPU transferring the ownership of the DES again can be
omitted. After specified times (ORM×IIN) of transfer have ended, if a new Start Trigger is issued, transfers
of the same details as the previous ones are started.
With DV set to 11, since the DSTC keeps having the ownership of the DES and does not return it to the
CPU, the transfer becomes an infinite loop process. To escape from the infinite loop of transfer, set DV to
"10" to return to CPU the ownership of the DES that has been transferred to the DSTC when DV was set
to "11".
The CPU can update the DES if DV is set to 00. If DV is set to 01, 10 or 11, the CPU cannot update
details of the DES area other than DV while the DSTC is executing the transfer according to that DES.
If DV[1] is set to 1, the DSTC reuses the values of the DES after executing ORM×IIN times of transfer.
Therefore, specific restrictions on reloading the transfer counter and transfer address are added. If DV[1]
is set to 1 and the settings of the DES make the values of DES1, DES2 and DES3 not return to their
respective values, the DSTC notifies the CPU a DES open error. For details, see “3.2.8 MONERS
Register”.
ST[1:0]
ST(Status)[1:0] of DES0 is for the DSTC to notify the CPU of the transfer end status. Table 3-10 shows
data the DSTC writes to ST in a DES close process.
Table 3-10 Content of ST Notification
After the transfer specified in a DES has ended, in a DES close process, the DSTC writes the end
status value to ST.
00: The transfer has ended normally.
01: The transfer has ended abnormally because an error occurred at a transfer source access.
10: The transfer has ended abnormally because an error occurred at a transfer destination access.
11: The transfer has ended abnormally because a transfer compulsory stopped by standby
transition command is issued from CPU.
If a transfer ends abnormally due to a DES access error or a DES open error, the DSTC does not execute
a DES close process and does not write data to ST because the DSTC cannot access the DES area.
Such error notifications are executed according to the MONERS Register of the DSTC but not ST of the
DES. For details, see 3.2.8 MONERS Register.
PCHK[3:0]
PCHK[3:0] (Parity Check) sets the parity (to be called equation below) of the DES0 area.
PCHK[3:0] != (DES0[27:24] ^ DES0[23:20] ^ DES0[19:16] ^ DES0[15:12] ^ DES0[11:8] ^ DES0[7:4])
If data in the DES area is corrupted by an event like a runaway of the CPU, the DSTC may start an
unintended transfer. The parity check function is installed in DES0 to prevent the above from occurring.
The CPU sets the parity of DES0 to PCHK when building the DES for the first time. The DSTC checks the
consistency between the values of PCHK and those of DES0 in the DES open process. If a parity error
occurs, the DSTC notifies the CPU of a DES open error and does not execute the transfer. For details,
see 3.2.8 MONERS Register.
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