MSC8144E Reference Manual, Rev. 3
17-10
Freescale
Semiconductor
RapidIO Interface Dedicated DMA Controller
descriptor address. As a result, two list descriptor fetches always exist after channel continue
before the first link descriptor fetch and the first transfer.
17.2.1.3 Channel Abort
Software can abort a previously initiated transfer by setting MRn[CA]. Once the DMA channel
controller detects a zero-to-one transition of MRn[CA], it finishes the current sub-block transfer
and halts all further activity. The controller then waits for all previously initiated transfers from
the specified channel to drain and clears SRn[CB]. Successful completion of a software initiated
abort request can be recognized by MRn[CA] being set and SRn[CB] being cleared. Obviously, if
the controller was already halted because of an error condition (SRn[TE] is set), or the channel
has completed all transfers, then SRn[CB] being cleared may not signify that the controller
entered a halt state due to the abort request.
17.2.1.4 Bandwidth Control
MRn[BWC] specifies how much data to allow a specific channel to transfer before allowing the
next channel to use the shared data transfer hardware. This promotes equitable bandwidth
allocation between channels. However, if only one channel is busy, hardware overrides the
specified bandwidth control size value. The DMA controller allows a channel to transfer up to 1
Kbyte at a time when no other channel is active.
17.2.1.5 Channel State
Table 17-2 defines the state of a channel based on the values of the channel start (MRn[CS]),
channel busy (SRn[CB]), transfer error (SRn[TE]), and channel continue (MRn[CC]) bits.
Table 17-2. Channel State Table
MRn[CS]
SRn[CB]
SRn[TE]
MRn[CC]
Channel State
0
0
0
0
Idle state. This is the state of the bits out of reset.
0
0
0
1
Channel continue unexpected. Channel remains idle
0
0
1
0
Error occurred after software halted the channel.
0
0
1
1
Channel Continue unexpected. Channel remains in error halt state
0
1
0
0
Software halted channel. The channel was busy and software cleared
MRn[CS].
0
1
0
1
Channel remains in halt state.
—
1
1
—
The channel has encountered an error condition and it is trying to halt.
1
0
0
0
Ready to start a transfer, or transfer completed
1
0
0
1
Continue transfer (only meaningful in chaining mode, not direct mode). In
direct mode, the channel continue has no effect.
1
0
1
0
Error occurred during transfer
1
0
1
1
Channel remains in error halt state
Содержание MSC8144E
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Страница 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
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