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General-Purpose Memory Controller
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Host byte read and write access requests to a 16-bit wide NAND device are completed as 16-bit accesses
on the device itself, because there is no byte-addressing capability on 16-bit wide NAND devices. This
means that the NAND device address pointer is incremented on a Word16 basis and not on a byte basis.
For a read access, only the requested byte is given back to the host, but the remaining byte is not stored
or saved by the GPMC, and the next byte or Word16 read access gets the next Word16 NAND location.
For a write access, the invalid byte part of the Word16 is driven to FF, and the next byte or Word16 write
access programs the next Word16 NAND location.
Generally, byte access to a 16-bit wide NAND device should be avoided, especially when ECC calculation
is enabled. 8-bit or 16-bit ECC-based computations are corrupted by a byte read to a 16-bit wide NAND
device, because the nonrequested byte is considered invalid on a read access (not captured on the
external data bus; FF is fed to the ECC engine) and is set to FF on a write access.
Host requests (read/write) issued in the chip-select memory region are translated in successive single or
split accesses (read/write) to the attached device. Therefore, incrementing 32-bit burst requests are
translated in multiple 32-bit sequential accesses following the access adaptation of the 32-bit to 8- or
16-bit device.
10.1.5.14.2 NAND Device-Ready Pin
The NAND memory device provides a ready pin to indicate data availability after a block/page opening
and to indicate that data programming is complete. The ready pin can be connected to one of the four
WAIT GPMC input pins; data read accesses must not be tried when the ready pin is sampled inactive
(device is not ready) even if the associated chip-select WAITREADMONITORING bit field is set. The
duration of the NAND device busy state after the block/page opening is so long (up to 50
m
s) that
accesses occurring when the ready pin is sampled inactive can stall GPMC access and eventually cause
a system time-out.
NOTE:
If a read access to a NAND flash is done using the wait monitoring mode, the device is
blocked during a page opening, and so is the GPMC. If the correct settings are used, other
chip-selects can be used while the memory processes the page opening command.
To avoid a time-out caused by a block/page opening delay in NAND flash, disable the wait
pin monitoring for read and write accesses (that is, set the GPMC.
[21]
WAITWRITEMONITORING and GPMC.
[22] WAITREADMONITORING
bits to 0, where i = 0 to 7), and use one of the following methods instead:
•
Use software to poll the WAITnSTATUS bit (n = 0 to 3) of the
register.
•
Configure an interrupt that is generated on the WAIT signal change (through the
GPMC.
register bits[11:8]).
Even if the READWAITMONITORING bit is not set, the external memory nR/B pin status is
captured in the programmed WAIT bit in the
register.
The READWAITMONITORING bit method must be used fo rmemories other than NAND
flash, if they require the use of a WAIT signal.
10.1.5.14.2.1 Ready Pin Monitored by Software Polling
The ready signal state can be monitored through the GPMC.
WAITxSTATUS bit (x = 0 to
3). The software must monitor the ready pin only when the signal is declared valid. See the NAND device
timing parameters to set the correct software temporization to monitor ready only after the invalid window
is complete from the last read command written to the NAND device.
10.1.5.14.2.2 Ready Pin Monitored by Hardware Interrupt
Each gpmc_wait input pin can generate an interrupt when a wait-to-no-wait transition is detected.
Depending on whether the GPMC.
WAITxPINPOLARITY bits (x = 0 to 3) is active low or
active high, the wait-to-no-wait transition is a low-to-high external WAIT signal transition or a high-to-low
external WAIT signal transition, respectively.
The wait transition pin detector must be cleared before any transition detection. This is done by writing 1
2162
Memory Subsystem
SWPU177N – December 2009 – Revised November 2010
Copyright © 2009–2010, Texas Instruments Incorporated
Содержание OMAP36 Series
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Страница 692: ...692 MPU Subsystem SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...
Страница 1084: ...1084 IVA2 2 Subsystem SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...
Страница 1990: ...1990 2D 3D Graphics Accelerator SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...
Страница 2334: ...2334 Memory Subsystem SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...
Страница 2700: ...2700 Memory Management Units SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...
Страница 2868: ...2868 HDQ 1 Wire SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...
Страница 2974: ...2974 UART IrDA CIR SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...
Страница 3054: ...3054 Multichannel SPI SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...
Страница 3462: ...3462 MMC SD SDIO Card Interface SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...
Страница 3508: ...3508 General Purpose Interface SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...
Страница 3584: ...3584 Initialization SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...
Страница 3648: ...3648 Debug and Emulation SWPU177N December 2009 Revised November 2010 Copyright 2009 2010 Texas Instruments Incorporated ...