Freescale Semiconductor MPC5553, Reference Manual

Page: 346 / 1208

MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor 9-27
161–166 /
0x14 [1:6]
CITER
[0:5]
or
CITER.LINKCH
[0:5]
Current “major” iteration count or link channel number.
If channel-to-channel linking is disabled (TCD.CITER.E_LINK = 0), then
• No channel-to-channel linking (or chaining) is performed after the inner minor
loop is exhausted. TCD bits [161:175] are used to form a 15-bit CITER field.
otherwise
• After the minor loop is exhausted, the eDMA engine initiates a channel service
request at the channel defined by CITER.LINKCH[0:5] by setting that channel’s
TCD.START bit.
167–175 /
0x14 [7:15]
CITER
[6:14]
Current “major” iteration count. This 9 or 15-bit count represents the current major
loop count for the channel. It is decremented each time the minor loop is completed
and updated in the transfer control descriptor memory. After the major iteration
count is exhausted, the channel performs a number of operations (for example, final
source and destination address calculations), optionally generating an interrupt to
signal channel completion before reloading the CITER field from the beginning
iteration count (BITER) field.
Note: When the CITER field is initially loaded by software, it must be set to the
same value as that contained in the BITER field.
Note: If the channel is configured to execute a single service request, the initial
values of BITER and CITER should be 0x0001.
176–191 /
0x14 [16:31]
DOFF
[0:15]
Destination address signed offset. Sign-extended offset applied to the current
destination address to form the next-state value as each destination write is
completed.
192–223 /
0x18 [0:31]
DLAST_SGA
[0:31]
Last destination address adjustment or the memory address for the next transfer
control descriptor to be loaded into this channel (scatter/gather).
If scatter/gather processing for the channel is disabled (TCD.E_SG = 0) then
• Adjustment value added to the destination address at the completion of the outer
major iteration count.
This value can be applied to “restore” the destination address to the initial value, or
adjust the address to reference the next data structure.
Otherwise
• This address points to the beginning of a 0-modulo-32 byte region containing the
next transfer control descriptor to be loaded into this channel. This channel
reload is performed as the major iteration count completes. The scatter/gather
address must be 0-modulo-32 byte, otherwise a configuration error is reported.
224 /
0x1C [0]
BITER.E_LINK Enables channel-to-channel linking on minor loop complete. As the channel
completes the inner minor loop, this flag enables the linking to another channel,
defined by BITER.LINKCH[0:5]. The link target channel initiates a channel service
request via an internal mechanism that sets the TCD.START bit of the specified
channel. If channel linking is disabled, the BITER value is extended to 15 bits in
place of a link channel number. If the major loop is exhausted, this link mechanism
is suppressed in favor of the MAJOR.E_LINK channel linking.
0 The channel-to-channel linking is disabled.
1 The channel-to-channel linking is enabled.
Note: When the TCD is first loaded by software, this field must be set equal to the
corresponding CITER field, otherwise a configuration error will be reported. As the
major iteration count is exhausted, the contents of this field is reloaded into the
CITER field.
Table 9-18. TCDn Field Descriptions (Continued)
Bits /
Word Offset [n:n]
Name Description