MOTOROLA
MC68341 USER’S MANUAL
9- 23
continues at either address $0 or at the address found in NEWQP, depending on the
state of WRTO. The QSPI continues looping until either WREN is negated, HALT is
asserted, or SPE is negated. Once WREN is negated, the QSPI finishes executing
commands through the command at the address contained in ENDQP, sets the SPIF
flag, and stops. When WREN is set, SPIF is set each time the QSPI transfers the entry
indicated by ENDQP.
WRTO—Wrap To
When wraparound mode is enabled and after the end of queue has been reached,
WRTO determines which address the QSPI executes next. End of queue is determined
by an address match with ENDQP. Execution wraps to address $0 if WRTO is not set,
or to the address found in NEWQP if WRTO is set.
Bit 12—Not Implemented
ENDQP—Ending Queue Pointer
This field determines the last absolute address in the queue to be completed by the
QSPI. After completing each command, the QSPI compares the queue pointer value of
the just-completed command with the value of ENDQP. If the two values match, the
QSPI assumes it has reached the end of the programmed queue and sets the SPIF flag
to so indicate.
The QSPI RAM queue has 16 entries: $0–$F. The user may program the NEWQP to
start executing commands, beginning at any of the 16 addresses. Similarly, the user
may program the ENDQP to stop execution of commands at any of the 16 addresses.
The queue is a circular data structure. If ENDQP is set to a lower address than
NEWQP, the QSPI executes commands through address $F, and then continues
execution at address $0 and so on until it stops after executing the command at address
ENDQP. A maximum of 16 commands are executed before stopping, unless
wraparound mode is enabled or unless the user modifies NEWQP and/or ENDQP.
The user may write a NEWQP value at any time, changing the flow of execution.
ENDQP may also be written at any time, changing the length of the queue. Wraparound
mode may also be enabled, causing continuous execution until the mode is disabled or
the QSPI is halted.
Bits 7–4—Not Implemented
NEWQP—New Queue Pointer Value
NEWQP determines which queue entry the QSPI transfers first. NEWQP should be
initialized before the QSPI is enabled with SPE. NEWQP may also be written while the
QSPI is operating. When this happens, the QSPI completes transfer of the queue entry
in progress and then immediately begins transferring queue entries starting with the
entry indicated by the NEWQP.
In this way, NEWQP provides additional functionality to the QSPI by providing a
mechanism for supporting multiple queues or subqueues within the QSPI RAM. By
changing the value in NEWQP, the user can cause the QSPI to execute a sequence of
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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