2.11.1.2 TR Pipelining
2.11.1.3 Performance Tuning
2.11.2 Error Generation
EDMA3 Transfer Controller (EDMA3TC)
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Table 2-15. Read/Write Command Optimization Rules
SAM/DAM =
ACNT
≤
DBS
ACNT is power of 2
BIDX = ACNT
BCNT
≤
1023
Increment
Description
Yes
Yes
Yes
Yes
Yes
Optimized
No
x
x
x
x
Not Optimized
x
No
x
x
x
Not Optimized
x
x
No
x
x
Not Optimized
x
x
x
No
x
Not Optimized
x
x
x
x
No
Not Optimized
TR pipelining refers to the ability of the source active set to get ahead of the destination active set.
Essentially, the reads for a given TR may already be in progress while the writes of a previous TR may
not have completed.
The number of outstanding TRs is limited by the number of destination FIFO register entries. A single TR
must be assured to target a single source peripheral endpoint.
TR pipelining is useful for maintaining throughput on back-to-back small TRs. It eliminates the read
overhead because reads start in the background of a previous TR writes.
By default, reads are as issued as fast as possible. In some cases, the reads issued by the EDMA3TC
could fill the available command buffering for a slave, delaying other (potentially higher priority) masters
from successfully submitting commands to that slave. The rate at which read commands are issued by the
EDMA3TC is controlled by the RDRATE register. The RDRATE register defines the number of cycles that
the EDMA3TC read controller waits before issuing subsequent commands for a given TR, thus minimizing
the chance of the EDMA3TC consuming all available slave resources. The RDRATE value should be set
to a relatively small value if the transfer controller is targeted for high priority transfers and to a higher
value if the transfer controller is targeted for low priority transfers.
In contrast, the Write Interface does not have any performance turning knobs because writes always have
an interval between commands as write commands are submitted along with the associated write data.
Errors are generated if enabled under three conditions:
•
EDMA3TC detection of an error signaled by the source or destination address.
•
Attempt to read or write to an invalid address in the configuration memory map.
•
Detection of a constant addressing mode TR violating the constant addressing mode transfer rules (the
source/destination addresses and source/destination indexes must be aligned to 32 bytes).
Either or all error types may be disabled. If an error bit is set and enabled, the error interrupt for the
concerned transfer controller is pulsed.
58
EDMA3 Architecture
SPRUG34 – November 2008
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