Enhanced Direct Memory Access Controller (eDMA)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 24-29
24.4 Functional Description
This section provides an overview of the microarchitecture and functional operation of the eDMA block.
250 /
0x1C [26]
MAJOR.E_LINK Enable channel-to-channel linking on major loop completion. As the channel completes
the outer major loop, this flag enables the linking to another channel, defined by
MAJOR.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.
Note: To support the dynamic linking coherency model, this field is forced to zero when
written to while the TCD.DONE bit is set.
0 The channel-to-channel linking is disabled.
1 The channel-to-channel linking is enabled.
251 /
0x1C [27]
E_SG Enable scatter-gather processing. As the channel completes the outer major loop, this
flag enables scatter-gather processing in the current channel. If enabled, the DMA
engine uses DLAST_SGA as a memory pointer to a 0-modulo-32 address containing a
32-byte data structure which is loaded as the transfer control descriptor into the local
memory.
Note: To support the dynamic scatter-gather coherency model, this field is forced to zero
when written to while the TCD.DONE bit is set.
0 The current channel’s TCD is normal format.
1 The current channel’s TCD specifies a scatter gather format. The DLAST_SGA field
provides a memory pointer to the next TCD to be loaded into this channel after the
outer major loop completes its execution.
252 /
0x1C [28]
D_REQ Disable hardware request. If this flag is set, the eDMA hardware automatically clears the
corresponding EDMA_ERQL bit when the current major iteration count reaches zero.
0 The channel’s EDMA_ERQL bit is not affected.
1 The channel’s EDMA_ERQL bit is cleared when the outer major loop is complete.
253 /
0x1C [29]
INT_HALF Enable an interrupt when major counter is half complete. If this flag is set, the channel
generates an interrupt request by setting the appropriate bit in the EDMA_IRQRL when
the current major iteration count reaches the halfway point. Specifically, the comparison
performed by the eDMA engine is (CITER == (BITER >> 1)). This halfway point interrupt
request is provided to support double-buffered (aka ping-pong) schemes, or other types
of data movement where the processor needs an early indication of the transfer’s
progress. CITER = BITER = 1 with INT_HALF enabled will generate an interrupt as it
satisfies the equation (CITER == (BITER >> 1)) after a single activation.
0 The half-point interrupt is disabled.
1 The half-point interrupt is enabled.
254 /
0x1C [30]
INT_MAJ Enable an interrupt when major iteration count completes. If this flag is set, the channel
generates an interrupt request by setting the appropriate bit in the EDMA_ERQL when
the current major iteration count reaches zero.
0 The end-of-major loop interrupt is disabled.
1 The end-of-major loop interrupt is enabled.
255 /
0x1C [31]
START Channel start. If this flag is set the channel is requesting service. The eDMA hardware
automatically clears this flag after the channel begins execution.
0 The channel is not explicitly started.
1 The channel is explicitly started via a software initiated service request.
Table 24-20. TCDn Field Descriptions (continued)
Bits /
Word Offset
[n:n]
Name Description
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