Freescale Semiconductor MPC8313E PowerQUICC II Pro Family Reference Manual page 507

Enhanced Local Bus Controller
Following the assertion of LALE, FCM asserts LCSn to commence a command sequence to the Flash
device. After a delay of t , the first command can be written to the device on assertion of LFWE,
CSCT
followed by any parameters (typically address bytes and data), and concluded with a secondary command.
In many cases, the second command initiates a long-running operation inside the Flash device, which pulls
the wired-OR pin LFRB low to indicate that the device is busy. Since in Figure 10-45 FCM is now
expecting a read response, it takes LBCTL low to turnaround any bus transceivers that are present. Upon
LFRB indicating ready status, FCM asserts LFRE repeatedly to recover bytes of read data, and the bytes
are stored in eLBC's FCM buffer RAM while an ECC is optionally computed on the bytes transferred.
Finally, FCM negates LCSn and delays eLBC by t before any subsequent memory access occurs.
EHTR
10.4.3.1 FCM Buffer RAM
Read and write accesses to eLBC banks controlled by FCM do not access attached NAND Flash
EEPROMs directly. Rather, these accesses read and write the FCM buffer RAM—a single, shared 8-Kbyte
space internal to eLBC and mapped by the base address of every FCM bank. Even though each
FCM-controlled bank will have a different base address to differentiate it, all accesses to such banks will
access the same buffer space. External eLBC signals, such as LALE and LCSn, will not assert upon
accesses to the buffer RAM. The FCM buffer RAM is logically divided into two or more buffers,
depending on the setting of ORn[PGS], with different buffers being accessible concurrently by software
and FCM.
To perform a page read operation from a NAND Flash device, software initializes the FCM command,
mode, and address registers, before issuing a special operation (FMR[OP] set non-zero) to a particular
FCM-controlled bank. FCM will execute the sequence of op-codes held in FIR, reading data from the
Flash device into the shared buffer RAM. While this read is taking place, software is free to access any
data stored in other, currently inactive buffers of the FCM buffer RAM through reads or writes to any bank
controlled by FCM. If command completion interrupts are enabled, an interrupt will be generated once
FCM has completed the read. When FCM has completed its last command, software can switch to the
newly read buffer and issue further commands.
To perform a page write operation, software first prepares data to be written in a fresh buffer. Then, the
FCM command, mode, and address registers are initialized, and a special operation (FMR[OP] set
non-zero) is issued to a particular FCM-controlled bank. FCM will execute the sequence of op-codes held
in FIR, writing data from shared buffer RAM to the Flash device. To ensure that the device is enabled for
programming, software must initialize FMR[OP] = 11, which prevents assertion of LFWP during the
write. While this write is taking place, software is free to access any data stored in other, currently inactive
buffers of the FCM buffer RAM through reads or writes to any bank controlled by FCM. When FCM has
completed its last command, software can re-use the previously written buffer and issue further
commands.
See Section 10.4.3.4.2, "Boot Block Loading into the FCM Buffer RAM," for a description of the shared
buffer RAM layout during boot.
10.4.3.1.1 Buffer Layout and Page Mapping for Small-Page NAND Flash Devices
The FCM buffer space is divided into eight 1-Kbyte buffers for small-page devices (ORn[PGS] = 0),
mapped as shown in Figure 10-46. Each page in a small-page NAND Flash comprises 528 bytes, where
MPC8313E PowerQUICC™ II Pro Integrated Processor Family Reference Manual, Rev. 2
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