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2014-07-02 - Tiny Gecko Family - d0034_Rev1.20
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8. The controller generates an auto-request for the channel and then arbitrates.
Task C
9. The controller performs task C. After it completes the task, it generates an
auto-request for the channel and then arbitrates.
Primary, copy D
10.The controller performs four DMA transfers. These transfers write the alternate
data structure for task D.
11.The controller sets the cycle_ctrl bits of the primary data structure to b000, to
indicate that this data structure is now invalid.
12.The controller generates an auto-request for the channel and then arbitrates.
Task D
13.The controller performs task D using an auto-request cycle.
14.The controller sets
dma_done[C]
HIGH for one
HFCORECLK
cycle and enters
the arbitration process.
8.4.2.3.6 Peripheral scatter-gather
In peripheral scatter-gather mode the controller receives an initial request from a peripheral and then it
performs four DMA transfers using the primary data structure. It then immediately starts a DMA cycle
using the alternate data structure, without re-arbitrating.
Note
These are the only circumstances, where the controller does not enter the arbitration
process after completing a transfer using the primary data structure.
After this cycle completes, the controller re-arbitrates and if the controller receives a request from the
peripheral that has the highest priority then it performs another four DMA transfers using the primary
data structure. It then immediately starts a DMA cycle using the alternate data structure, without re-
arbitrating. The controller continues to switch from primary to alternate to primary… until either:
• the host processor configures the alternate data structure for a basic cycle
• it reads an invalid data structure.
Note
After the controller completes the N primary transfers it invalidates the primary data
structure by setting the cycle_ctrl field to b000.
The controller asserts
dma_done[C]
when the scatter-gather transaction completes using a basic cycle.
In scatter-gather mode, the controller uses the primary data structure to program the alternate data
structure. Table 8.5 (p. 56) lists the fields of the channel_cfg memory location for the primary data
structure, that you must program with constant values and those that can be user defined.
Table 8.5. channel_cfg for a primary data structure, in peripheral scatter-gather mode
Bit
Field
Value
Description
Constant-value fields:
[31:30]
dst_inc
b10
Configures the controller to use word increments for the address
[29:28]
dst_size
b10
Configures the controller to use word transfers
[27:26]
src_inc
b10
Configures the controller to use word increments for the address
[25:24]
src_size
b10
Configures the controller to use word transfers
[17:14]
R_power
b0010
Configures the controller to perform four DMA transfers
[2:0]
cycle_ctrl
b110
Configures the controller to perform a peripheral scatter-gather DMA cycle
User defined values:
[23:21]
dst_prot_ctrl
-
Configures the state of
HPROT
when the controller writes the destination data
Summary of Contents for EFM32TG
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