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GPMC
The wait transition pin detector must be cleared before any transition detection. This is done by writing 1
to the WAITxEDGEDETECTIONSTATUS bit (x = 0 or 1) of the GPMC_IRQSTATUS register according to
the gpmc_wait pin used for the NAND device-ready signal monitoring. To detect a wait-to-no-wait
transition, the transition detector requires a wait active time detection of a minimum of two GPMC_FCLK
cycles. Software must incorporate precautions to clear the wait transition pin detector before wait (busy)
time completes.
A wait-to-no-wait transition detection can issue a GPMC interrupt if the WAITxEDGEDETECTIONENABLE
bit in the GPMC_IRQENABLE register is set and if the WAITxEDGEDETECTIONSTATUS bit field in the
GPMC_IRQSTATUS register is set.
The WAITMONITORINGTIME field does not affect wait-to-no-wait transition time detection.
It is also possible to poll the WAITxEDGEDETECTIONSTATUS bit field in the GPMC_IRQSTATUS
register according to the gpmc_wait pin used for the NAND device ready signal monitoring.
7.1.3.3.12.3 ECC Calculator
The General Purpose Memory Controller includes an Error Code Correction (ECC) calculator circuitry that
enables on the fly ECC calculation during data read or data program (that is, write) operations. The page
size supported by the ECC calculator in one calculation/context is 512 bytes.
The user can choose from two different algorithms with different error correction capabilities through the
GPMC_ECC_CONFIG[16] ECCALGORITHM bit:
• Hamming code for 1-bit error code correction on 8- or 16-bit NAND Flash organized with page size
greater than 512 bytes
• BCH (Bose-Chaudhurl-Hocquenghem) code for 4- to 16-bit error correction
The GPMC does not directly handle the error code correction itself. During writes, the GPMC computes
parity bits. During reads, the GPMC provides enough information for the processor to correct errors
without reading the data buffer all over again.
The Hamming code ECC is based on a 2-dimensional (row and column) bit parity accumulation. This
parity accumulation is either accomplished on the programmed number of bytes or 16-bit words read from
the memory device, or written to the memory device in stream mode.
Because the ECC engine includes only one accumulation context, it can be allocated to only one chip-
select at a time through the GPMC_ECC_CONFIG[3-1] ECCCS bit field. Even if two CS use different ECC
algorithms, one the Hamming code and the other a BCH code, they must define separate ECC contexts
because some of the ECC registers are common to all types of algorithms.
7.1.3.3.12.3.1 Hamming Code
All references to Error Code Correction (ECC) in this subsection refer to the 1-bit error correction
Hamming code.
The ECC is based on a two-dimensional (row and column) bit parity accumulation known as Hamming
Code. The parity accumulation is done for a programmed number of bytes or 16-bit word read from the
memory device or written to the memory device in stream mode.
There is no automatic error detection or correction, and it is the software NAND driver responsibility to
read the multiple ECC calculation results, compare them to the expected code value, and take the
appropriate corrective actions according to the error handling strategy (ECC storage in spare byte, error
correction on read, block invalidation).
The ECC engine includes a single accumulation context. It can be allocated to a single designated chip-
select at a time and parallel computations on different chip-selects are not possible. Since it is allocated to
a single chip-select, the ECC computation is not affected by interleaved GPMC accesses to other chip-
selects and devices. The ECC accumulation is sequentially processed in the order of data read from or
written to the memory on the designated chip-select. The ECC engine does not differentiate read
accesses from write accesses and does not differentiate data from command or status information. It is
the software responsibility to make sure only relevant data are passed to the NAND flash memory while
the ECC computation engine is active.
309
SPRUH73H–October 2011–Revised April 2013 Memory Subsystem
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