GPMC
The device system issues only requests with addresses or starting addresses for nonwrapping burst
requests; that is, the request size boundary is aligned. In case of an eight-word-wrapping burst, the
wrapping address always occurs on the eight-words boundary. As a consequence, all words requested
must be available from the memory data buffer when the buffer size is equal to or greater than the
ATTACHEDDEVICEPAGELENGTH value. This usually means that data can be read from or written to the
buffer at a constant rate (number of cycles between data) without wait states between data accesses. If
the memory does not behave this way (nonzero wait state burstable memory), wait-pin monitoring must be
enabled to dynamically control data-access completion within the burst.
When the system burst request length is less than the ATTACHEDDEVICEPAGELENGTH value, the
GPMC proceeds with the required accesses.
7.1.3.3.11 pSRAM Access Specificities
pSRAM devices are SRAM-pin-compatible low-power memories that contain a self-refreshed DRAM
memory array. The GPMC_CONFIG1_i[[11-10] DEVICETYPE field shall be cleared to 0b00.
The pSRAM devices uses the NOR protocol. It support the following operations:
•
Asynchronous single read
•
Asynchronous page read
•
Asynchronous single write
•
Synchronous single read and write
•
Synchronous burst read
•
Synchronous burst write (not supported by NOR Flash memory)
pSRAM devices must be powered up and initialized in a predefined manner according to the specifications
of the attached device.
pSRAM devices can be programmed to use either mode: fixed or variable latency. pSRAM devices can
either automatically schedule autorefresh operations, which force the GPMC to use its WAIT signal
capability when read or write operations occur during an internal self-refresh operation, or pSRAM devices
automatically include the autorefresh operation in the access time. These devices do not require additional
WAIT signal capability or a minimum CSn high pulse width between consecutive accesses to ensure that
the correct internal refresh operation is scheduled.
7.1.3.3.12 NAND Access Description
NAND (8-bit and 16-bit) memory devices using a standard NAND asynchronous address/data-multiplexing
scheme can be supported on any chip-select with the appropriate asynchronous configuration settings
As for any other type of memory compatible with the GPMC interface, accesses to a chip-select allocated
to a NAND device can be interleaved with accesses to chip-selects allocated to other external devices.
This interleaved capability limits the system to chip enable don't care NAND devices, because the chip-
select allocated to the NAND device must be de-asserted if accesses to other chip-selects are requested.
7.1.3.3.12.1 NAND Memory Device in Byte or 16-Bit Word Stream Mode
NAND devices require correct command and address programming before data array read or write
accesses. The GPMC does not include specific hardware to translate a random address system request
into a NAND-specific multiphase access. In that sense, GPMC NAND support, as opposed to random
memory-map device support, is data-stream-oriented (byte or 16-bit word).
The GPMC NAND programming model relies on a software driver for address and command formatting
with the correct data address pointer value according to the block and page structure. Because of NAND
structure and protocol interface diversity, the GPMC does not support automatic command and address
phase programming, and software drivers must access the NAND device ID to ensure that correct
command and address formatting are used for the identified device.
NAND device data read and write accesses are achieved through an asynchronous read or write access.
The associated chip-select signal timing control must be programmed according to the NAND device
timing specification.
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SPRUH73H – October 2011 – Revised April 2013
Memory Subsystem
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