GPMC
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7.1.3.3.12.4.7 Interleaved Accesses Between Prefetch and Write-Posting Engine and Other Chip-Selects
Any on-going read or write access from the prefetch and write-posting engine is completed before an
access to any other chip-select can be initiated. As a default, the arbiter uses a fixed-priority algorithm,
and the prefetch and write-posting engine has the lowest priority. The maximum latency added to access
starting time in this case equals the RDCYCLETIME or WRCYCLETIME (optimized or not) plus the
requested BUSTURNAROUND delay for bus turnaround completion programmed for the chip-select to
which the NAND device is connected to.
Alternatively, a round-robin arbitration can be used to prioritize accesses to the external bus. This
arbitration scheme is enabled by setting the GPMC_PREFETCH_CONFIG1[23] PFPWENROUNDROBIN
bit. When a request to another chip-select is received while the prefetch and write-posting engine is active,
priority is given to the new request. The request processed thereafter is the prefetch and write-posting
engine request, even if another interconnect request is passed in the mean time. The engine keeps
control of the bus for an additional number of requests programmed in the
GPMC_PREFETCH_CONFIG1[19-16] PFPWWEIGHTEDPRIO bit field. Control is then passed to the
direct interconnect request.
As an example, the round-robin arbitration scheme is selected with PFPWWEIGHTEDPRIO set to 2h.
Considering the prefetch and write-posting engine and the interconnect interface are always requesting
access to the external interface, the GPMC grants priority to the direct interconnect access for one
request. The GPMC then grants priority to the engine for three requests, and finnaly back to the direct
interconnect access, until the arbiter is reset when one of the two initiators stops initiating requests.
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Memory Subsystem SPRUH73H–October 2011–Revised April 2013
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