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•
In
Figure
5-26, the RDCYCLETIME programmed value equals RDCYCLETIME0 (before paged
accesses) + RDCYCLETIME1 (after paged accesses).
5.2.4.10.3.4 Synchronous Operations on a Nonmultiplexed Device
All information for this section is equivalent to similar operations for address/data- or AAD-multiplexed
accesses. The only difference resides in the address phase. See
5.2.4.10.4 Page and Burst Support
Each chip-select can be configured to process system single or burst requests into successive single
accesses or asynchronous page/synchronous burst accesses, with appropriate access size adaptation.
Depending on the external device page or burst capability, read and write accesses can be
independently configured through the GPMC. The GPMC_CONFIG1_i[30] READMULTIPLE and
GPMC_CONFIG1_i[28] WRITMULTIPLE bits (i = 0 to 7) are associated with the READTYPE and
WRITETYPE parameters.
•
Asynchronous write page mode is not supported.
•
8-bit wide device support is limited to nonburstable devices (READMULTIPLE and
WRITEMULTIPLE are ignored).
•
Not applicable to NAND device interfacing.
5.2.4.10.5 System Burst Versus External Device Burst Support
The device system can issue the following requests to the GPMC:
•
Byte, 16-bit word, 32-bit word requests (byte enable controlled). This is always a single request from
the interconnect point of view.
•
Incrementing fixed-length bursts of two words, four words, and eight words
•
Wrapped (critical word access first) fixed-length burst of two, four, or eight words
To process a system request with the optimal protocol, the READMULTIPLE (and READTYPE) and
WRITEMULTIPLE (and WRITETYPE) parameters must be set according to the burstable capability
(synchronous or asynchronous) of the attached device.
The GPMC access engine issues only fixed-length burst. The maximum length that can be issued is
defined per CS by the GPMC_CONFIG1_i[24-23] ATTACHEDDEVICEPAGELENGTH field (i = 0 to 7).
When the ATTACHEDDEVICEPAGELENGTH value is less than the system burst request length
(including the appropriate access size adaptation according to the device width), the GPMC splits the
system burst request into multiple bursts. Within the specified 4-, 8-, or 16-word value, the
ATTACHEDDEVICEPAGELENGTH field value must correspond to the maximum-length burst
supported by the memory device configured in fixed-length burst mode (as opposed to continuous burst
mode).
To get optimal performance from memory devices that natively support 16 Word16-length-wrapping
burst capability (critical word access first), the ATTACHEDDEVICEPAGELENGTH parameter must be
set to 16 words and the GPMC_CONFIG1_i[31] WRAPBURST bit (i = 0 to 7) must be set to 1. Similarly
DEVICEPAGELENGTH is set to 4 and 8 for memories supporting respectively 4 and 8
Word16-length-wrapping burst.
When the memory device does not offer (or is not configured to offer) native 16
Word16-length-wrapping burst, the WRAPBURST parameter must be cleared, and the GPMC access
engine emulates the wrapping burst by issuing the appropriate burst sequences according to the
ATTACHEDDEVICEPAGELENGTH value.
When the memory device does not support native-wrapping burst, there is usually no difference in
behavior between a fixed burst length mode and a continuous burst mode configuration (except for a
potential power increase from a memory-speculative data prefetch in a continuous burst read).
However, even though continuous burst mode is compatible with GPMC behavior, because the GPMC
access engine issues only fixed-length burst and does not benefit from continuous burst mode, it is best
to configure the memory device in fixed-length burst mode.
SPRUGX9 – 15 April 2011
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Preliminary
© 2011, Texas Instruments Incorporated
Section
5.3.3.
General-Purpose Memory Controller (GPMC)
Architecture
599
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