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µDMA Channel Control Structure Registers
625
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Micro Direct Memory Access (µDMA)
Table 8-16. DMACHCTL Register Field Descriptions (continued)
Bit
Field
Type
Reset
Description
2-0
XFERMODE
R/W
X
µDMA Transfer Mode
This field configures the operating mode of the µDMA cycle. See
for a detailed explanation of transfer modes.
Because this register is in system RAM, it has no reset value.
Therefore, this field should be initialized to 0 before the channel is
enabled.
0x0 = Stop
0x1 = Basic
0x2 = Auto-Request
0x3 = Ping-Pong
0x4 = Memory Scatter-Gather
0x5 = Alternate Memory Scatter-Gather
0x6 = Peripheral Scatter-Gather
0x7 = Alternate Peripheral Scatter-Gather
Table 8-17. XFERMODE Bit Field Values
Mode
Description
Stop
Channel is stopped or configuration data is invalid. No more transfers can occur.
Basic
For each trigger (whether from a peripheral or a software request), the µDMA controller performs the number
of transfers specified by the ARBSIZE field.
Auto-Request
The initial request (software- or peripheral-initiated) is sufficient to complete the entire transfer of XFERSIZE
items without any further requests.
Ping-Pong
This mode uses both the primary and alternate control structures for this channel. When the number of
transfers specified by the XFERSIZE field have completed for the current control structure (primary or
alternate), the µDMA controller switches to the other one. These switches continue until one of the control
structures is not set to ping-pong mode. At that point, the µDMA controller stops. An interrupt is generated
on completion of the transfers configured by each control structure. See
Memory Scatter-
Gather
When using this mode, the primary control structure for the channel is configured to allow a list of operations
(tasks) to be performed. The source address pointer specifies the start of a table of tasks to be copied to the
alternate control structure for this channel. The XFERMODE field for the alternate control structure should be
configured to 0x5 (Alternate memory scatter-gather) to perform the task. When the task completes, the
µDMA switches back to the primary channel control structure, which then copies the next task to the
alternate control structure. This process continues until the table of tasks is empty. The last task must have
an XFERMODE value other than 0x5. Note that for continuous operation, the last task can update the
primary channel control structure back to the start of the list or to another list. See
.
Alternate Memory
Scatter-Gather
This value must be used in the alternate channel control data structure when the µDMA controller operates
in Memory Scatter-Gather mode.
Peripheral Scatter-
Gather
This value must be used in the primary channel control data structure when the µDMA controller operates in
Peripheral Scatter-Gather mode. In this mode, the µDMA controller operates exactly the same as in Memory
Scatter-Gather mode, except that instead of performing the number of transfers specified by the XFERSIZE
field in the alternate control structure at one time, the µDMA controller only performs the number of transfers
specified by the ARBSIZE field per trigger; see Basic mode for details. See
Alternate Peripheral
Scatter-Gather
This value must be used in the alternate channel control data structure when the µDMA controller operates
in Peripheral Scatter-Gather mode.