Texas Instruments OMAP5912 Reference Manual page 181

3.9 Priority Algorithms
SPRU749A
The traffic controller provides a choice of two priority algorithms for
simultaneous requests. Arbitration is performed in each TC target port
(OCP-T1, OCP-T2, EMIFF, and EMIFS).
Selection of the arbitration scheme is common to all TC ports. Depending on
the OMAP device, it can be either hardwired to one of the two algorithms or
programmable (outside of OMAP).
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Enhanced round robin with LRU
In accordance with the standard round-robin scheme, the requestor hav-
ing the highest priority becomes the lowest-priority requestor after it has
been granted access.
The first enhancement is that when it gets the highest priority, a requestor
can keep it for a programmable number of consecutive accesses.
The number of consecutive accesses is individually programmable for the
MPU, DSP, the system DMA, and OCP-I. See OCPT1_PRIORITY,
OCPT2_PRIORITY, EMIF_SLOW_PRIORITY, and EMIF_FAST_PRIOR-
ITY registers.
In parallel with the round-robin scheme, the second enhancement is that
the least recently granted requestor always has the highest priority. That
means if a requestor has missed its slot because it had no request pending
at that time, it keeps the highest priority for the subsequent arbitration
cycles.
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Dynamic priority order
Most of the time, the priority order is fixed: highest priority is MPU, then
DSP, OCP-I, and lowest priority is DMA. A programmable time-out is
attached to any host except the MPU to ensure that it is not blocked indefi-
nitely by higher priority hosts.
When a low-priority requestor gains the arbitration (i.e. DSP, OCP-I,
DMA), the associated time-out counter is loaded with the programmed
value and starts decrementing.
If a counter reaches 0, the associated requestor gets the highest priority
for its next request (that may be already pending). If several requestors are
in this situation, the priority order is: DMA LCD, DSP, OCP-I, DMA other
than LCD.
Traffic Controller
OMAP3.2 Subsystem 123